PCB Process Design Specification

1. Purpose

Standardize the PCB process design of products, specify the relevant parameters of PCB process design, and ensure that the PCB design meets the requirements for production

The technical specifications for performance, testability, safety, EMC, EMI, etc. are required to construct the process and technology of the product during the product design process

Advantages in technology, quality, and cost.

2. Scope of application

This specification applies to the PCB process design of all electrical products, including but not limited to PCB design and PCB layout

Activities such as art review and veneer process review.

If the content of relevant standards and specifications before this specification conflicts with the provisions of this specification, this specification shall prevail.

3. Definition

Via: a metalized hole used for inner layer connections, but not for inserting component leads or other reinforcements

Material Science.

Blind via: A conductive hole that extends from the inside of a printed circuit board to only one surface layer.

Buried via: A type of conductive hole that does not extend to the surface of a printed circuit board.

Through via: A conductive hole that extends from one surface of a printed circuit board to another surface.

Component hole: A hole used for fixing component terminals to printed boards and electrically connecting conductive patterns.

Stand off: The vertical distance from the bottom of the surface mount device to the bottom of the pins.

4. Quoting/referencing standards or materials

TS-S0902010001<<Information Technology Equipment PCB Safety Design Specification>>

TS-SOE0199001<<Design Specification for Forced Wind Heating and Cooling of Electronic Equipment>>

TS-SOE0199002<<Design Specification for Natural Cooling Heat of Electronic Equipment>>

IEC60194<<Printed Circuit Board Design, Manufacturing, and Assembly Terminology and Definitions>>

manufacture and assembly-terms and definitions）

IPC-A-600F<<Acceptable of Printed Board>>

IEC60950

5. Standardized content

5.1 PCB board requirements

5.1.1 Determine the PCB board and TG value to be used

Determine the selected PCB board, such as FR-4, aluminum substrate, ceramic substrate, paper core board, etc. If high TG value is selected

The thickness tolerance of the board should be indicated in the document.

5.1.2 Determine the surface treatment coating of PCB

Determine the surface treatment coating for PCB copper foil, such as tin plating, nickel gold plating, or OSP, and indicate it in the document.

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5.2 Thermal Design Requirements

5.2.1 High temperature components should be considered to be placed at the air outlet or in a location conducive to convection

In the layout of PCB, consider placing high heat components at the air outlet or in positions that are conducive to convection.

5.2.2 Higher components should be considered to be placed at the air outlet and not obstruct the air path

5.2.3 The placement of radiators should consider facilitating convection

5.2.4 Temperature sensitive devices should be considered to be kept away from heat sources

For heat sources with a temperature rise above 30 ℃, the general requirements are:

a. Under air-cooled conditions, temperature sensitive components such as electrolytic capacitors must be at least 2.5mm away from the heat source;

b. Under natural cold conditions, temperature sensitive devices such as electrolytic capacitors are required to be at least 4.0mm away from the heat source.

If the required distance cannot be reached due to space constraints, temperature testing should be conducted to ensure that the temperature rise of the temperature sensitive device is within the rated range

Within the scope.

5.2.5 Large area copper foil is required to be connected to the solder pads with heat insulation tape

In order to ensure good tin penetration, the solder pads of components on large-area copper foils are required to be connected to the solder pads with heat barriers. For components that require a 5A rating

The above high current pads cannot use insulated pads, as shown in the figure:

 

Figure 1

5.2.6 Heat dissipation symmetry of solder pads at both ends of 0805 and below chip components subjected to reflow soldering

In order to avoid misalignment and standing phenomenon of the device after reflow soldering, 0805 and chip components below 0805 are reflow soldered to the ground

The two end solder pads should ensure symmetrical heat dissipation, and the width of the connection between the solder pad and the printed conductor should not exceed 0.3mm (for asymmetric solder pads),

As shown in Figure 1.

5.2.7 Installation method of high heat devices and whether consideration is given to including heat sinks

Ensure that the installation method of high-temperature components is easy to operate and solder. In principle, when the heating density of the components exceeds 0.4W/cm3

Due to insufficient heat dissipation of the lead legs and components themselves, measures such as heat dissipation networks and busbars should be taken to improve the overcurrent energy

The support legs of the busbar should be connected at multiple points, and riveting and wave soldering or direct wave soldering should be used as much as possible to facilitate installation

Assembly and welding; For the use of longer bus bars, consideration should be given to the mismatch between the thermal expansion coefficient of the bus bar and the PCB during peak heating

The PCB is deformed.

In order to ensure easy operation of tinning, the width of the solder path should not be greater than or equal to 2.0mm, and the distance between the edges of the solder path should be greater than 1.5mm.

5.3 Requirements for Device Library Selection

5.3.1 The selection of existing PCB component packaging libraries should be confirmed to be correct

The selection of components from the existing component library on the PCB should ensure that the packaging matches the physical outline, pin spacing, through-hole diameter, etc. of the components

Consistent with.

The wiring at both ends of the solder pad is evenly distributed

Connect the solder pads with equivalent heat capacity to the copper foil in a "meter" or "cross" shape

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The pins of the plug-in device should fit well with the tolerance of the through-hole (the through-hole diameter should be 8-20mil larger than the pin diameter), considering that the tolerance may be appropriate

When increasing, ensure good tin penetration.

The aperture of the component is serialized, with increments of 5 mil for sizes above 40mil, i.e. 40 mil, 45 mil, 50 mil, 55 mil;

Below 40 mil, decrease by 4 mil, i.e. 36 mil, 32 mil, 28 mil, 24 mil, 20 mil, 16 mil, 12 mil, 8 mil

The correspondence between the diameter of device pins and the aperture of PCB solder pads, as well as the solder pads for reflow soldering of secondary power supply pins and through holes

The correspondence between aperture sizes is shown in Table 1:

Device pin diameter (D) PCB pad aperture/pin through-hole reflow soldering pad aperture

D≦1.0mm D+0.3mm/+0.15mm 

1.0mm<D≦2.0mm D+0.4mm/0.2mm 

D>2.0mm D+0.5mm/0.2mm 

Table 1

When establishing component packaging inventory, the unit of aperture should be converted to British units (mil) and the aperture should meet serialization requirements.

5.3.2 The PCB component packaging inventory of new devices should be confirmed to be accurate

For components that do not have a packaging library on the PCB, a salvaged component packaging library should be established based on the component information, and silk screen inventory should be ensured

Whether the inventory of components, especially newly established electromagnetic components, self-made structural components, etc., is consistent with the material of the components (acknowledged)

The books and drawings are consistent. New devices should be established to meet the requirements of different processes (reflow soldering, wave soldering, through-hole reflow soldering)

Component library.

5.3.3 SMT devices that require wave soldering require the use of surface mount wave soldering pad libraries

5.3.4 The types of pin spacing for axial devices and jumpers should be minimized to reduce the need for device shaping and installation tools.

5.3.5 Compatible devices with different PIN spacing should have separate pad holes, especially for the compatible pads of encapsulated relays

Connect between them.

5.3.6 The solder pads of jumper wires such as manganese copper wire used for measurement should be made non-metallic. If the solder pads are metalized, then after welding

The resistance inside the panel will be short circuited, and the effective length of the resistance will become smaller and inconsistent, resulting in inaccurate test results.

5.3.7 Surface mount devices cannot be used as manual soldering test devices, as surface mount devices are prone to thermal shock damage during manual soldering.

5.3.8 Unless there is no problem with experimental verification, pinless surface mount devices with significantly different thermal expansion coefficients from PCBs cannot be selected,

This can easily cause the phenomenon of solder pad detachment.

Unless there are no issues with experimental verification, non surface mount devices cannot be selected for use as surface mount devices. Because this may require

Hand welding results in low efficiency and reliability.

When using partial copper plating on the side of a multi-layer PCB for soldering pins, it is necessary to ensure that each layer is connected by copper foil to increase plating

The adhesion strength of copper should be verified through experiments, otherwise the double-sided board cannot use copper plating on the side as the soldering pin.

5.4 Basic Layout Requirements

5.4.1 Reasonable PCBA processing procedures

The layout of the components used to make the board should ensure that the processing procedures are reasonable, in order to improve the efficiency and pass rate of the board manufacturing process.

The processing flow selected for PCB layout should achieve the highest processing efficiency.

The 6 mainstream processing flows for commonly used PCBA are shown in Table 2:

5.4.2 The direction of board entry for wave soldering processing requires silk screen marking

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The direction of board entry for wave soldering should be indicated on the PCB and made reasonable. If the PCB can be made from two different directions

The direction of the incoming board should be marked with double arrows. For reflow soldering, it is possible to consider using fixtures to determine its reflow soldering process

Direction).

Table 2

5.4.3 The BOTTOM surface of PCB with double-sided reflow soldering requires no large volume or heavy surface mount components to be reflow soldered on both sides

The weight limit for the first reflow soldering of PCB components is as follows:

A=Device weight/Contact area between pins and pads

Chip device: A ≤ 0.075g/mm2

Wing shaped pin device: A ≤ 0.300g/mm2

J-shaped pin device: A ≤ 0.200g/mm2

Surface array device: A ≤ 0.100g/mm2

If there are overweight components that must be placed on the BOTTOM surface, feasibility should be verified through testing.

5.4.4 Safety distance for single board backside devices that require wave soldering processing to avoid shadow effects has been considered for SMT machines using wave soldering technology

The distance requirements for the item are as follows:

1) Distance between devices of the same type (see Figure 2)

 

Serial number

Name Process Characteristics Applicable Scope

1. Single sided insertion molding - plug-in - high efficiency of wave soldering, with PCB assembly heating times of one

second

The device is THD

Single sided solder paste printing, surface mounting, and reflow soldering have high efficiency, with PCB assembly heating times of one

second

The device is SMD

3 Single sided mixed solder paste printing - SMT - reflow soldering - THD -

Wave soldering

High efficiency, PCB assembly heating times are

secondary

The device is

SMD、THD 

4. Double sided mixed patch offset printing brush - SMT - curing - flipping plate

- THD - Wave soldering - Flip board - Manual soldering

High efficiency, with two heating cycles for PCB assembly

second

The device is

SMD、THD 

5 double-sided adhesive

Plug in installation

Solder paste printing - SMT - Reflow soldering - Flip board -

Solder paste printing - SMT - reflow soldering - manual soldering

High efficiency, with two heating cycles for PCB assembly

second

The device is

SMD、THD 

6 Conventional Wave Soldering

Double sided mixed packaging

Solder paste printing - SMT - Reflow soldering - Flip board -

SMT offset printing brush - SMT - curing - flipping plate

- THD - Wave soldering - Flip board - Manual soldering

Low efficiency, PCB assembly heating times are

Three times

The device is

SMD、THD 

L

B B

L

L 

B 

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Crossing the peak direction

Figure 2

 

The relationship between packaging size and distance for devices of the same type (Table 3):

Pad spacing L (mm/mil) Device body spacing B (mm/mil)

Minimum recommended spacing

0603 0.76/30 1.27/50 0.76/30 1.27/50 

0805 0.89/35 1.27/50 0.89/35 1.27/50 

1206 1.02/40 1.27/50 1.02/40 1.27/50 

≧1206 1.02/40 1.27/50 1.02/40 1.27/50 

SOT package 1.02/40 1.27/50 1.02/40 1.27/50

Tantalum capacitors 3216, 3528 1.02/40 1.27/50 1.02/40 1.27/50

Tantalum capacitors 6032, 7343 1.27/50 1.52/60 2.03/80 2.54/100

SOP 1.27/50 1.52/60 --- --- 

Table 3

2) Distance between different types of devices (see Figure 3)

Crossing the peak direction

Figure 3

Table 4 shows the relationship between packaging size and distance for different types of devices:

Package size 0603 0805 1206 ≥ 1206 SOT package tantalum capacitor tantalum capacitor SOIC through-hole

06.3 1.27 1.27 1.27 1.52 1.52 2.54 2.54 1.27

0805 1.27 1.27 1.27 1.52 1.52 2.54 2.54 1.27

1206 1.27 1.27 1.27 1.52 1.52 2.54 2.54 1.27

≧1206 1.27 1.27 1.27 1.52 1.52 2.54 2.54 1.27

SOT package 1.52 1.52 1.52 1.52 2.54 2.54 1.27

Tantalum capacitors 3216, 3528 1.52 1.52 1.52 1.52 2.54 2.54 1.27

B 

B

B

B

B

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Tantalum capacitors 6032, 7343 2.54 2.54 2.54 2.54 2.54 2.54 1.27

SOIC 2.54 2.54 2.54 2.54 2.54 2.54 2.54 1.27

Through hole 1.27 1.27 1.27 1.27 1.27 1.27 1.27 1.27 1.27 1.27

Table 4

Ceramic capacitors with a size greater than 0805 should be arranged as close as possible to the transmission edge or areas with less stress, and their axial direction should be as close as possible to the transmission edge

Parallel to the board direction (Figure 4), try not to use ceramic capacitors with dimensions above 1825. (Reserved opinion)

Entering board direction

Reduce stress and prevent component cracking. High stress can easily cause component cracking

Figure 4

5.4.6 Regularly plugging and unplugging components or board edge connectors should avoid placing SMD within a 3mm range to prevent the occurrence of connector plugging and unplugging

The stress generated damages the device. As shown in Figure 5:

Try not to arrange SMD within 3mm around the connector as much as possible

Figure 5

5.4.7 The stand off of surface mount devices subjected to wave soldering meets the specification requirements

The stand off of surface mount devices that have undergone wave soldering should be less than 0.15mm, otherwise they cannot be placed on the B-side for wave soldering

The stand off of the component is between 0.15mm and 0.2mm, and copper foil can be laid underneath the device body to reduce the distance between the bottom of the device body and the PCB

Surface distance.

5.4.8 The minimum safe distance for back test points not connected to tin during wave soldering has been determined

To ensure that there is no solder connection during wave soldering, the distance between the edges of the back test points should be greater than 1.0mm.

5.4.9 The distance between the solder pads of plug-in components that have undergone wave soldering is greater than 1.0mm

To ensure that there is no solder connection during wave soldering, the edge spacing of the solder pads of the plug-in components that have undergone wave soldering should be greater than 1.0mm (including components)

The edge spacing between the solder pads of the pins themselves.

Preferred plug-in components have a pitch of ≥ 2.0mm and a pad edge spacing of ≥ 1.0mm.

On the premise that the device body does not interfere with each other, the spacing between adjacent device pad edges meets the requirements of Figure 6:

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Min 1.0mm 

Figure 6

When there are more pins in each row of plug-in components and the devices are arranged parallel to the direction of the incoming board in the direction of the solder pad arrangement, when adjacent solder pad edges

When the edge spacing is 0.6mm-1.0mm, it is recommended to use elliptical solder pads or solder pads (Figure 7).

Stealing solder pads for board direction

Elliptical solder pad

 d1 X 

 d2 

 D1 D2 

 Y 

Figure 7

5.4.10 No components within 3mm around BGA

To ensure maintainability, there should be a 3mm no go zone around the BGA device, preferably a 5mm no go zone. General situation

BGA is not allowed to be placed on the back side under certain conditions (the first reflow soldering surface of a single board that has undergone reflow soldering twice); When the back has

When using BGA devices, devices cannot be placed within the projection range of the BGA5mm prohibited area on the front side.

5.4.11 The minimum spacing between surface mount components meets the requirements

Requirements for device distance between machine mounted components (Figure 8):

Same type of device: ≥ 0.3mm

Heterogeneous devices: ≥ 0.13 * h+0.3mm (h is the maximum height difference between neighboring components)

The distance requirement between components that can only be manually mounted is ≥ 1.5mm.

device

 

X or Y

Same type of device, different type of device

Figure 8

5.4.12 The distance between the outer side of the component and the two board edges in contact with the board track is greater than or equal to 5mm (Figure 9)

X 

pitch

X=0.6*pitch 

Y=aperture+16~20mil

When X<Y, choose elliptical pads

When X>Y, choose elliptical solder pads

D1=D2 

d1=d2 

Suction nozzle

PCB 

X

Y

h

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X X 

X 

Prohibited area for devices with X ≥ 5mm

Figure 9

In order to ensure that the clamp of the transport track does not touch the components during wave soldering or reflow soldering of the board, the outer side of the components is far away from the board

The edge distance should be greater than or equal to 5mm. If it does not meet the requirements, the PCB should be processed with edges, and the distance between the device and the V-CUT should be ≥ 1mm.

5.4.13 There should be sufficient space around adjustable and pluggable devices for debugging and maintenance

The arrangement of adjustable devices should be comprehensively considered based on the PCBA installation layout of the system or module and the testing method of adjustable devices

Layout direction and measurement space; The reserved space around pluggable devices should be determined based on the height of adjacent devices.

5.4.14 All plug-in magnetic components must have a sturdy base, and the use of unsupported plug-in inductors is prohibited

5.4.15 The pins of transformers with polarity should not be designed in a symmetrical form as much as possible

5.4.16 No components or wiring within the prohibited area of the installation hole (excluding wiring and copper foil of the installation hole itself)

5.4.17 The distance between metal shell components and metal components and other components meets safety requirements

The arrangement of metal shell components and metal parts should ensure that the distance from other components meets safety requirements in space.

5.4.18 Requirements for Layout of Through Hole Reflow Soldering Devices

a. For PCBs with non transmission edge sizes greater than 300mm, heavier components should be avoided from being placed in the middle of the PCB as much as possible,

To reduce the impact of the weight of the plug-in components on PCB deformation during the soldering process, as well as the impact of the plug-in process on the board

The impact of devices that have been pasted.

b. For ease of insertion and installation, it is recommended to place the device near the insertion operation side.

c. It is recommended that the length direction of devices with longer dimensions, such as memory module sockets, be consistent with the transmission direction.

PCB board direction

Figure 10

d. QFP, SOP, connectors, and all BGA with through-hole reflow soldering device pad edge and pitch ≤ 0.65mm

The distance between silk screens is greater than 10mm. The distance between other SMT components is greater than 2mm.

e. The distance between the main bodies of through-hole reflow soldering devices is greater than 10mm. There are no requirements for welding pins supported by fixtures.

Example: Pin using through-hole reflow soldering

≧10mm

≧5mm 

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f. The distance between the edge of the solder pad and the transfer edge of the through-hole reflow soldering device is greater than 10mm; Distance from non transmitting edge>5mm.

5.4.19 Requirements for Prohibited Areas of Through Hole Reflow Soldering Devices

a. Sufficient space should be left around the solder pads of through-hole reflow soldering devices for solder paste coating. The specific prohibited area requirements are:

There should be no devices in the direction of 10.5mm inside the European connector board, and there should be no devices or vias in the prohibited area.

b. The through holes that need to be placed in the prohibited area should be treated with solder mask plug holes.

5.4.20 Device layout should consider overall single board assembly interference

When designing the layout of devices, it is necessary to consider the assembly interference between single boards and single boards, as well as between single boards and structural components, especially for high devices

Stereoscopic assembly of single boards, etc.

5.4.21 Distance requirements between devices and chassis

When arranging components, it is important to avoid placing them too close to the chassis wall to prevent damage to the components when installing the PCB into the chassis. especially

Pay attention to components installed at the edge of the PCB that may experience slight movement or lack a sturdy appearance during impact and vibration, such as:

If the above requirements cannot be met by installing resistors or transformers without bases, additional fixing measures must be taken to meet them

Foot safety regulations and vibration requirements.

5.4.22 Devices that have undergone wave soldering should be arranged at the edge of the PCB as much as possible to facilitate hole blocking. If the device is arranged at the edge of the PCB, and

The installation fixture is well done, and there is even no need to block holes during wave soldering.

5.4.23 When designing and laying out PCBs, it is advisable to allow devices to pass through wave soldering as much as possible. When selecting components, try to choose as few as possible and avoid wave soldering

The number of components placed on the welding surface should be minimized to reduce manual welding.

5.4.24 Bare jumper wires should not be attached to the board to cross the wires or copper skin on the board, in order to avoid short circuits with the copper skin on the board. Green oil should not be used as an effective measure

The insulation.

5.4.25 When laying out, consideration should be given to the ease of inspection and maintenance of all components after welding.

5.4.26 The welding end of the cable should be arranged as close as possible to the edge of the PCB for insertion and welding, otherwise other components on the PCB will hinder it

The insertion and welding of cables or being skewed by cables.

Devices with multiple pins on the same straight line, such as connectors, DIP packaged devices, and T220 packaged devices, should be laid out in such a way that

Its axis is parallel to the wave soldering direction. (Figure 11)

Figure 11

5.4.28 For lighter devices such as diodes and 1/4W resistors, the layout should be perpendicular to the axis and wave soldering direction. This can prevent

During wave soldering, the device experiences a floating phenomenon due to one end being soldered and solidified first. (Figure 12)

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Figure 12

5.4.29 There should be a certain space between the cable and surrounding devices, otherwise the bent part of the cable will compress and damage the surrounding devices

Its solder joints.

5.5 Wiring Requirements

5.5.1 Distance between printed circuit board and board edge: V-CUT edge is greater than 0.75mm, milling groove edge is greater than 0.3mm.

In order to ensure that there are no defects of exposed copper during PCB processing, it is required that all wiring and copper foil distances from the board edge: V-CUT edge

Greater than 0.75mm, milling groove edge greater than 0.3mm (the distance between copper foil and board edge should also meet installation requirements).

5.5.2 No wiring below the front of the radiator (or insulated)

In order to ensure electrical insulation, there should be no wiring around the area below the radiator (considering the deviation and safety distance of the radiator installation)

If wiring is required under the heat sink, insulation measures should be taken to isolate the heat sink from the wiring, or confirm that the wiring is

The radiator has the same potential.

5.5.3 No wiring under the metal handle strip

To ensure electrical insulation, there should be no wiring underneath the metal handle strip.

5.5.4 Requirements for the Prohibited Area of Various Screw Holes

The prohibited area for various specifications of screws is shown in Table 5 below (this prohibited area is only applicable to ensuring electrical insulation)

Installation space, without considering safety distance, and only applicable to circular holes):

Connection type, model, specification, installation hole (mm), prohibited area (mm)

M2 2.4±0.1 φ7.1

M2.5 2.9±0.1 φ7.6

M3 3.4±0.1 φ8.6

M4 4.5±0.1 φ10.6

Screw connection GB9074.4-8 combination screw

M5 5.5±0.1 φ12

Su pull type quick rivet Chobert 4 4.10

-0.2 φ7.6

1189-2812 2.80

-0.2 φ6

Rivet connection

Connector quick rivet Avtronuic

1189-2512 2.50

-0.2 φ6

ST2.2* 2.4±0.1 φ7.6

ST2.9 3.1±0.1 φ7.6

Self tapping screw connection GB9074.18-88 cross disc head

Self attacking screws

ST3.5 3.7±0.1 φ9.6

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ST4.2 4.5±0.1 φ10.6

ST4.8 5.1±0.1 φ12

ST2.6* 2.8±0.1 φ7.6

Table 5

For devices with installation holes within the scope of the body, such as rivet holes and screw installation holes of sockets, in order to ensure electrical insulation,

The prohibited distribution areas should also be clearly marked in the component library.

5.5.5 It is necessary to increase the width of isolated solder pads and wiring connections (like teardrop soldering), especially for single panel solder pads, to avoid

Do not pull off the solder pad during wave soldering.

The prohibited areas for waist shaped long holes are shown in Table 6 below:

Connection type, model, specification, installation hole diameter (width), Dmm, installation hole length, Lmm, prohibited area (mm), L * D

M2 2.4 ± 0.1 confirmed by actual situation

L<D

φ7.6×(L+4.7)

M2.5 2.9±0.1 φ7.6×(L+4.7)

M3 3.4±0.1 φ8.6×(L+5.2)

M4 4.5±0.1 φ10.6×(L+6.1)

Screw connection

meet

GB9074.4—8

Combination screw

M5 5.5±0.1 φ12×(L+6.5)

Table 6

5.6 Requirements for fixed holes, installation holes, and through holes

5.6.1 The installation holes and positioning holes that need to be grounded on the top and bottom of the board that passes through the peak should be designated as right non-metallic holes.

5.6.2 The through-hole diameter under BGA is 12mil

5.6.3 The minimum distance between the edge of the SMT pad and the edge of the conductive area is 10 mil. If the via plug is filled with green oil, the minimum distance is 6 mil.

5.6.4 There are no conductive holes on the solder pads of SMT devices (note: except for the solder pads of DPAK packages used for heat dissipation)

5.6.5 Normally, standard via hole sizes should be used

The standard via hole size (aperture to plate thickness ratio ≤ 1:6) is shown in Table 7:

Inner diameter (mil) Outer diameter (mil)

12 25 

16 30 

20 35 

24 40 

32 50 

Table 7

5.6.6 For boards that have undergone wave soldering, if there are components mounted on the component surface, there should be no through holes underneath or the through holes should be covered with green oil.

5.7 Benchmark requirements

5.7.1 PCB boards with surface mount components shall have at least two asymmetric reference points diagonally (Figure 13)

Panel benchmark unit benchmark point

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Local reference point

Figure 13

The reference point is used for optical positioning during solder paste printing and component mounting. According to the reference points on the PCB, it can be divided into assembly

Board reference point, unit reference point, local reference point. There should be at least two asymmetric reference points on the PCB.

5.7.2 The center of the reference point is greater than 5mm from the edge of the board and is protected by a metal ring

a. Shape: The preferred shape for the reference point is a solid circle.

b. Size: The preferred size for the reference point is a diameter of 40mil ± 1mil.

c. Material: The material of the reference point is bare copper or coated copper. In order to increase the contrast between the reference point and the substrate, it can be used in the base

Lay the large copper foil on time below.

5.7.3 Correct benchmark spot welding disc and solder mask settings (Figure 14)

Solder mask window: The shape of the solder mask is a circle concentric with the reference point, with a size twice the diameter of the reference point. At a diameter of 80mil

Reference point metal protective ring

FR-4 reference point solder mask

Copper foil

D1 d1 d D 

D1=110mil D=80mil solder mask area

D1=90mil d=40mil 

Figure 14

A circular copper wire is required as a protective ring at the edge, and the diameter of the metal protective ring is: outer diameter 110mil, inner diameter

90mil, with a line width of 10mm. Due to the small space of the unit reference point, a metal protective ring can be omitted. Recommended benchmark for multi-layer boards

Lay copper on the inner layer to increase recognition contrast.

The reference points for aluminum substrate and thick copper foil (copper foil thickness ≥ 30Z) are different, as shown in Figure 15. The setting of the reference point is:

On a copper foil with a diameter of 80mil, open a solder mask window with a diameter of 40mil.

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Figure 15

5.7.4 No other wiring or silk screen printing within the reference point range

In order to ensure the recognition effect of printing and SMT, there should be no other wiring or screen printing within the reference point range.

5.7.5 For single boards that require splicing, try to ensure that there are reference points on the unit board as much as possible

Single boards that require splicing should have reference points on each unit board as much as possible. If it is not possible to lay them on the unit board due to space constraints

When setting reference points, reference points can be omitted from the unit board, but it should be ensured that there are reference points in the splicing process.

5.8 Screen printing requirements

5.8.1 All components, mounting holes, and positioning holes have corresponding silk screen labels

In order to facilitate the installation of the PCB, all components, mounting holes, and positioning holes have corresponding silk screen labels

The installation holes are marked with H1, H2... Hn for silk screen printing.

5.8.2 Silk screen characters follow the principle of left to right and bottom to top

Screen printing characters should follow the principle of left to right and bottom to top as much as possible. For devices with polarity such as electrolytic capacitors and diodes

Try to maintain consistent orientation within each functional unit.

5.8.3 There should be no silk screen on the solder pads and solder paths that require tinning, and the device tag number should not be obscured by the device after installation. (High density,

Items on PCB that do not require screen printing (except for a few)

To ensure the welding reliability of the device, it is required that there is no silk screen on the device pads; In order to ensure the continuity of the tinning process, it is necessary to

Request that there is no silk screen on the tin track that needs to be tinned; For the convenience of device insertion and maintenance, the device tag number should not be obscured by the installed device

Block; Silk screen printing should not be pressed onto conductive holes or solder pads to avoid partial loss of silk screen printing when opening solder mask windows, which may affect training. silk

The printing distance is greater than 5ml.

5.8.4 Polarized components have their polarity clearly indicated on the silk screen, making it easy to identify the polarity direction markings.

5.8.5 Directional connectors have their direction clearly indicated on the silk screen.

5.8.6 There should be barcode position identification on the PCB

If the space on the PCB board allows, there should be a 42 * 6 barcode silk screen frame on the PCB, and the position of the barcode should be considered

Convenient for scanning.

5.8.7 The silk screen position of PCB board information such as board name, date, and version number should be clearly defined.

The PCB file should have printed board information such as board name, date, and version number, with clear and prominent positions.

5.8.8 The PCB should have complete manufacturer information and anti-static markings.

5.8.9 The number of PCB light drawing files is correct, and each layer should have correct output and complete layer output.

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5.8.10 The identifiers of components on the PCB must be consistent with the identification symbols in the BOM list.

5.9 Safety requirements

5.9.1 The safety markings of the insurance tube are complete

Are there 6 complete markings near the fuse, including fuse number, melting characteristics, rated current value, and explosion-proof features

Sex, rated voltage value, and English warning signs.

Such as F101 F3.15AH, 250Vac, "CAUTION: For Continued Protection Against Risk of Fire,

Replace Only With Same Type and Rating of Fuse” 。

If there is no space to arrange English warning signs on the PCB, the warning signs can be placed in the product manual

explain.

5.9.2 Marking High Voltage Warning Symbols in Hazardous Voltage Areas on PCB

The hazardous voltage area of the PCB should be isolated from the safe voltage area with a 40mil wide dashed line, and a high-voltage hazard label should be printed on it

Identify "DANGER! HIGH VOTAGE". The high voltage warning symbol is shown in Figure 16:

 

Figure 16

5.9.3 Clear identification of original and auxiliary isolation belts

The original and side isolation tapes of the PCB are clear, with dotted lines in the middle.

5.9.4 PCB board safety labeling should be clearly defined

Five safety markings on PCB board (UL certification mark, manufacturer, manufacturer model, UL certification file number, flame retardant rating)

Complete.

5.9.5 Strengthen the electrical clearance and creepage distance of the insulation isolation tape to meet the requirements

The electrical clearance and creepage distance of the reinforced insulation isolation tape on the PCB meet the requirements. For specific parameter requirements, please refer to the relevant information

Technical Equipment PCB Safety Design Specification>>.

Devices relying on isolation strips need to meet the above requirements even under a thrust of 10N.

Except for the effective basic insulation from the casing to the pins of the safety capacitor, the casing of other devices is not considered to have insulation

Effective insulation, certified insulation sleeves and tapes are considered effective insulation.

5.9.6 Basic insulation isolation tape electrical clearance and creepage distance meet the requirements

The safety distance between the primary device casing and the grounded casing meets the requirements.

The safety distance between the shell of the primary device and the grounding screw meets the requirements.

The safety distance between the shell of the primary device and the grounding heat sink meets the requirements. (The specific distance size is determined by checking the table)

DANGER!!! 

HIGH VOLTAGE

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5.9.7 The cables used for crossing hazardous and safe areas (original side) on the board should meet the safety regulations for strengthening insulation

5.9.8 Considering a thrust of 10N, the components on both sides near the transformer core should meet the requirement of strengthening insulation

5.9.9 Considering a thrust of 10N, devices close to suspended metal conductors should meet the requirement of reinforced insulation

5.9.10 For multi-layer PCBs, the copper foil on the inner side of the original side should meet the requirements of electrical clearance creepage distance (pollution level according to)

According to calculation I)

5.9.11 For multi-layer PCBs, the distance near the via holes (including the inner layer) should meet the requirements of electrical clearance and creepage distance

5.9.12 For multi-layer PCB layers, the dielectric thickness between the primary and secondary sides must be ≥ 0.4mm

Interlayer thickness refers to the thickness of the medium (excluding copper foil thickness), including 2-3, 4-5, 6-7, 8-9, 10-11

Core boards are used between layers, while semi cured sheets are used between other layers.

5.9.13 A minimum safety distance of 2mm should be ensured between exposed welding terminals of different voltages. After insertion and welding, the welding terminals should be welded

Possible tilting and tilting may cause the distance to decrease.

Table 8 lists the default symmetric structures and interlayer thickness settings:

Type interlayer medium thickness (mm)

1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12

1.6mm four layer board 0.36 0.71 0.36

2.0mm four layer board 0.36 1.13 0.36

2.5mm four layer board 0.40 1.53 0.40

3.0mm four layer board 0.40 1.93 0.40

1.6mm six layer board 0.24 0.33 0.21 0.33 0.24

2.0mm six layer board 0.24 0.46 0.36 0.46 0.24

2.5mm six layer board 0.24 0.71 0.36 0.71 0.24

3.0mm six layer board 0.24 0.93 0.40 0.93 0.24

1.6mm eight layer board 0.14 0.24 0.14 0.24 0.14 0.24 0.14

2.0mm eight layer board 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24

2.5mm eight layer board 0.40 0.24 0.36 0.24 0.24 0.40

3.0mm eight layer board 0.40 0.41 0.36 0.41 0.36 0.41 0.40

1.6mm ten layer board 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14

2.0mm ten layer board 0.24 0.14 0.24 0.14 0.14 0.24 0.14 0.24 0.14 0.24

2.5mm Ten layer board 0.24 0.24 0.24 0.21 0.24 0.24 0.24 0.24

3.0mm ten layer board 0.24 0.33 0.24 0.33 0.36 0.33 0.24 0.33 0.24

2.0mm 12 layer board 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14

2.5mm 12 layer board 0.24 0.14 0.24 0.14 0.24 0.14 0.24 0.14 0.24 0.14 0.24 0.14 0.24

3.0mm 12 layer board 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24

Table 8

5.10 PCB size and appearance requirements

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5.10.1 The PCB size and thickness have been marked and determined in the PCB file, and the dimension marking should consider the manufacturer's processing tolerance.

Plate thickness (± 10% tolerance) specifications: 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm, 2.5mm, 3.0mm

3.5mm 

5.10.2 PCB board corners should be R-shaped chamfers

For the convenience of veneer processing, the corners of plywood without splicing should be R-shaped chamfers. For plywood with process edges and splicing, the process

The edge should have an R-shaped chamfer, with a general fillet diameter of Φ 5, and the small plate can be adjusted appropriately. Special requirements should be clearly marked according to the structural diagram representation method

Provide R size for manufacturers to process.

5.10.3 PCBs with dimensions less than 50mm X 50mm should be assembled (excluding aluminum and ceramic substrates)

General principle: When the size of the PCB unit board is less than 50mm x 50mm, splicing must be done;

When V-CUT is required for splicing, the PCB thickness of the splicing should be less than 3.5mm;

Best: The number of V-CUT lines parallel to the conveying edge direction is ≤ 3 (except for slender veneers);

As shown in Figure 17:

4-V-CUT 

2 V-CUTs

Auxiliary edge

Transport direction Transport direction

Preferred not recommended

Figure 17

In order to facilitate the separation of boards, positioning holes need to be added.

5.10.4 Irregular panel milling groove spacing greater than 80mil.

When irregular splicing requires milling grooves and V-cut method, the spacing between milling grooves should be greater than 80mil.

5.10.5 Irregular shaped PCBs without splicing should be processed with decorative edges

PCBs with irregular shapes that make board processing difficult should have their edges machined on both sides of the board passing direction.

The tolerance for the aperture of the 5.10.6 PCB should be+0.1mm.

5.10.7 If there are large areas of openings on the PCB, the holes should be filled in during design to avoid solder spreading and board deformation during soldering

The shape, completion part, and original PCB part should be connected at a few points on one side, and removed after wave soldering (Figure 18)

Original PCB

Figure 18

5.11 Process requirements

Complete Part

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5.11.1 When the BOTTOM surface mount device needs to pass through the peak, it should be confirmed that the layout direction of the mounted resistive capacitive component and SOP is correct

The axial direction of the component should be consistent with the direction of the wave peak.

a. SOP devices require an additional pair of tin stealing disks to be connected at the end of the peak. The dimensions meet the requirements of Figure 19.

Over peak direction over peak direction

 

b. SOT devices should strive to meet the optimal direction for peak crossing.

Crossing the peak direction

c. Chip type full terminal devices (resistors, capacitors) do not have special requirements for the direction of peak crossing.

d. The optimal direction for peak crossing of chip type non full terminal devices (tantalum capacitors, diodes) must be parallel to the axial direction and the incoming board direction

that 's ok. (Figure 20)

Crossing the peak direction

Figure 20

5.11.2 Surface mount devices such as SOJ, PLCC, QFP, etc. cannot be subjected to wave soldering.

The PIN spacing of SOP for wave soldering is greater than 1.0mm, and the chip component is above 0603.

5.12 Testability Requirements

5.12.1 Whether to use test points for testing.

If the board is not tested using test points, there are no requirements for the following items 5.12.2~5.12.15.

5.12.2 There should be two or more positioning holes on the PCB (positioning holes cannot be waist shaped).

2d d/2

Stealing solder pads 1.27mm 1.27mm solder thickness

Figure 19A

d

Figure 19b

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5.12.3 The size of the positioning should meet the requirement of a diameter of (3-5cm).

5.12.4 The positioning hole position on the PCB should be asymmetric

5.12.5 There should be process edges that comply with the specifications

5.12.6 For finished boards with a length or width greater than 200mm, there should be low pressure rod points that meet the specifications

5.12.7 The pin spacing of the device to be tested should be a multiple of 2.54mm

5.12.8 SMT component pads cannot be used as test points

5.12.9 Test points should be located on the welding surface (secondary power supply is not required)

5.12.10 The shape and size of the test points should comply with the specifications

It is recommended to choose square pads for testing points (circular pads are also acceptable), and the pad size should not be less than 1mm * mm.

5.12.11 Test points should be labeled (marked with TP1, TP2...).

5.12.12 All test points should have been solidified (when changing test points on the PCB, the properties must be modified to move the position).

5.12.13 The spacing between tests should be greater than 2.54mm.

The distance between the testing point and the components on the welding surface should be greater than 2.54mm.

The distance between low voltage testing points and high voltage testing points should comply with safety regulations.

The distance from the test point to the edge of the PCB board should be greater than 125mil/3.175mm.

The distance from the testing point to the positioning hole should be greater than 0.5mm to provide a certain amount of clear space for the positioning column.

5.12.18 The density of test points cannot exceed 4-5 per square centimeter; The test points need to be evenly distributed.

5.12.19 Requirements for testing points of power and ground.

Each test pin can withstand a maximum current of 2A, and for every additional 2A, an additional test point is required for both the power supply and ground.

For digital logic boards, generally every 5 ICs should provide a ground test point.

5.12.21 The height of the soldering surface components cannot exceed 150mil/3.81mm. If it exceeds this value, the list of ultra-high components should be notified to the equipment worker

Master Cheng, for special handling.

5.12.22 Whether to use connectors or cables for testing.

If the result is negative, there are no requirements for items 5.12.23 and 5.12.24.

The spacing between the pins of the 5.12.23 connector should be a multiple of 2.54mm.

5.12.24 All test points should have been connected to the connectors.

5.12.25 Adjustable devices should be used.

5.12.26 For ICT testing, each node must undergo testing; For functional testing, adjust points, grounding points, AC inputs, and discharge electricity

There should be testing points for surface mount devices that require testing.

5.12.27 Test points cannot be blocked by barcodes or covered by glue.

If the single board needs to be sprayed with "three proof paint", the test pads must be specially treated to avoid affecting the reliable contact of the probes.

6. Appendix

Distance and related safety requirements

Safe distance includes electrical clearance (spatial distance), creepage distance (along distance)

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1. Electrical clearance: The shortest distance measured along the air between two adjacent conductors or one conductor and the surface of an adjacent motor casing.

2. Creepage distance: the shortest distance measured along the insulation surface between two adjacent conductors or one conductor and the adjacent motor casing surface.

Determination of electrical clearance:

Based on the measured working voltage and insulation level, the distance can be determined

The electrical clearance size requirements for the primary side circuit are shown in Tables 3 and 4

The electrical clearance size requirements for the secondary side circuit are shown in Table 5

But usually: primary side AC part: L-N ≥ 2.5mm in front of the fuse, L.N PE (ground) ≥ 2.5mm, fuse device

Afterwards, no requirements are required, but try to maintain a certain distance as much as possible to avoid short circuits and damage to the power supply.

Primary side AC to DC part ≥ 2.0mm

Primary side DC ground to ground ≥ 2.5mm (primary side floating ground to ground)

Components that span between the primary and secondary sides with a length of ≥ 4.0mm from the primary side to the secondary side

The electrical gap gap of the secondary side should be ≥ 0.5mm

Secondary side ground to ground ≥ 1.0mm is sufficient

Note: Before deciding whether to meet the requirements, internal parts should be subjected to a force of 10N and the outer shell should be subjected to a force of 30N to reduce their distance and ensure that

Confirmed as the worst-case scenario, the spatial distance still meets the regulations.

Determination of creepage distance:

According to the working voltage and insulation level, the creepage distance can be determined by referring to Table 6

But usually: (1) Primary side AC part: L-N ≥ 2.5mm in front of the fuse, L.N ground ≥ 2.5mm, after the fuse can

No requirements are made, but try to maintain a certain distance to avoid short circuit damage to the power supply.

(2) Primary side AC to DC part ≥ 2.0mm

(3) Primary side DC ground to ground ≥ 4.0mm, such as primary side ground to ground

(4) If the distance between the pins of components such as optocouplers and Y capacitors is ≤ 6.4mm, slotting is required.

(5) The distance between the secondary side parts should be ≥ 0.5mm

(6) Secondary lateral ground to ground ≥ 2.0mm or more

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(7) Transformer with a distance of ≥ 8.0mm between two stages

3. Insulation penetration distance:

According to the working voltage and insulation application, the following regulations should be met:

——No thickness requirement for working voltage not exceeding 50V (71V AC peak or DC value);

——The minimum thickness of additional insulation should be 0.4mm;

——When the reinforced insulation does not withstand any mechanical stress that may cause deformation or performance degradation of the insulation material at normal temperatures

The minimum thickness for strengthening insulation should be 0.4mm.

If the insulation provided is used inside the protective casing of the equipment and will not be bumped or scratched during operator maintenance,

And if it belongs to any of the following situations, the above requirements do not apply to thin insulation materials regardless of their thickness;

——For additional insulation, at least two layers of materials should be used, each of which can pass the electrical strength test for the additional insulation;

Or:

——An additional insulation composed of three layers of materials, where any combination of two layers of materials can pass the electrical strength test of the additional insulation;

Or:

——For strengthening insulation, at least two layers of materials should be used, each of which can pass the electrical strength test for strengthening insulation;

Or:

——A reinforced insulation composed of three layers of insulating materials, where any combination of two layers of materials can enhance the electrical strength of the insulation

Experiment.

4. Regarding wiring process considerations:

Flat mount components such as capacitors must be flat mounted without the need for glue

If the distance between two conductors can be shortened by applying a force of 10N, and it is less than the safety distance requirement, the part can be fixed with glue to ensure its electrical integrity

Air gap.

When laying PVC film inside some shell equipment, attention should be paid to ensuring the safety distance (pay attention to the processing technology)

Attention should be paid to ensuring that there are no foreign objects such as glue threads on the PCB board when fixing the parts with adhesive.

When processing parts, insulation damage should not be caused.

5. Regarding the requirements for fire-resistant materials:

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Heat shrink tubing V-1 or VTM-2 or above; PVC sleeve V-1 or VTM-2 or above

Teflon sleeve V-1 or VTM-2 or above; Plastic materials such as silicone film, insulation tape V-1 or VTM-2 or above

PCB board 94V-1 or above

6. Regarding insulation grade

(1) Work insulation: the insulation required for the normal operation of equipment

(2) Basic insulation: insulation that provides basic protection against electric shock

(3) Additional insulation: an independent insulation applied in addition to the basic insulation to protect against the failure of the basic insulation

Prevent electric shock

(4) Double insulation: insulation composed of basic insulation and additional insulation

(5) Strengthening insulation: a single insulation structure that provides protection against electric shock under the conditions specified in this standard

Equivalent to double insulation level

 

The applicable scenarios for various types of insulation are as follows:

A、 Operational insulation

a、 Between two parts with different voltages

b、 Between ELV circuit (or SELV circuit) and grounded conductive components.

B、 Basic insulation

a、 Between hazardous voltage components and grounded conductive components;

b、 Between hazardous voltage and SELV circuits that rely on grounding;

c、 Between the power conductor on the primary side and the grounding shield or the iron core of the main power transformer;

d、 As part of double insulation.

C、 Supplementary insulation

a、 Generally speaking, there may be dangerous voltages present in accessible conductor parts and after basic insulation damage

Between the parts, such as:

I. Between the surface of a handle, knob, handle or similar object and its ungrounded axis.

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II. Between the metal casing of the second type of equipment and the outer shell of the power cord passing through this casing.

III. Between ELV circuit and ungrounded metal casing.

b、 As part of double insulation

D、 Double insulation

Double insulation Reinforced insulation 

Generally speaking, between the primary side circuit and

a、 Between accessible ungrounded conductive parts, or

b、 Between floating SELV circuits or

c. Between TNV circuits

Double insulation=basic insulation+supplementary insulation

Note: ELV circuit: Extra low voltage circuit

Under normal working conditions, the peak AC voltage between conductors or between any conductors shall not exceed 42.4V or DC

A secondary circuit with a value not exceeding 60V.

SELV circuit: safe extra low voltage circuit.

A secondary circuit that has been appropriately designed and protected, so that under normal conditions or single fault conditions, any

The protective grounding terminal between two touchable components, as well as any touchable component and equipment (only applicable to

The voltage between Class I devices will not exceed the safe value.

TNV: Communication Network Voltage Circuit

A circuit that carries communication signals under normal working conditions.