PCB Process Design Specification

1. Purpose

Standardize the PCB process design of the product, stipulate the relevant parameters of the PCB process design, so that the PCB design meets the technical specifications of manufacturability, testability, safety, EMC, EMI, etc., and build the product process, Technology, quality, and cost advantages.

2. Scope of application

This specification applies to the PCB process design of all electronic products, and is applied to but not limited to PCB design, PCB board process review, veneer process review and other activities. If the content of relevant standards and specifications before this specification conflict with the provisions of this specification, this specification shall prevail.

3. Definition

• Via: A metalized hole used for inner layer connection, but it is not used for inserting component leads or other reinforcing materials.
• Blind via: A via hole extending from the inside of the printed board to only one surface layer.
• Buried via: A via hole that does not extend to the surface of the printed board.
• Through-hole (Through via): a through-hole extending from one surface layer of the printed board to another surface layer.
• Component hole: A hole used for fixing component terminals on the printed board and electrically connecting with conductive patterns.
• Standoff: The vertical distance from the bottom of the body of the surface mount device to the bottom of the pin.

4. References/reference standards or materials

• TS—S0902010001 <>
• TS—SOE0199001 <>
• TS—SOE0199002 <>
• IEC60194 <> (Printed Circuit Board design manufacture and assembly-terms and definitions)
• IPC—A—600F <> (Acceptably of printed board)
• IEC60950

Normative content

1.  PCB board requirements

• 5.1.1 Determine the board used for PCB and TG value-determine the board selected for PCB, such as FR-4, aluminum substrate, a ceramic substrate, paper core board, etc. If a board with a high TG value is selected, the thickness should be indicated in the document tolerance.
• 5.1.2 Determine the surface treatment coating of the PCB-determine the surface treatment coating of the PCB copper foil, such as tin plating, nickel plating or OSP, etc., and indicate in the document.

Thermal design requirements

2. High-heat components should be placed in the air outlet or a location conducive to convection. In the PCB layout, consider placing high-heat components at the air outlet or at a location that is conducive to convection.

3. Higher components should be placed in the air outlet and should not block the air path

4. The placement of the radiator should be considered conducive to convection

5. Temperature-sensitive instruments should be kept away from heat sources. For heat sources whose temperature rises above 30°C, the general requirements are as follows:

• a. Under air-cooled conditions, the distance between electrolytic capacitors and other temperature-sensitive devices from the heat source must be greater than or equal to 2.5mm;
• b. Under natural cold conditions, the distance between electrolytic capacitors and other temperature-sensitive devices from the heat source must be greater than or equal to 4.0mm.

If the required distance cannot be reached due to space reasons, a temperature test should be conducted to ensure that the temperature rise of the temperature-sensitive device is within the derating range.

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6. Large-area copper foil requires thermal insulation tape to be connected to the pad
In order to ensure good tin penetration, the pads of the components on the large-area copper foil are required to be connected to the pads with thermal insulation tape. The above high-current pads cannot use thermal insulation pads, as shown in the figure:

7. Heat dissipation symmetry of the pads at both ends of the reflowed 0805 and below 0805 chip components
In order to avoid the deviation and tombstone phenomenon of the device after reflow soldering, ground reflow soldered 0805 and below 0805 chip components
The pads at both ends should ensure the symmetry of heat dissipation, and the width of the connection between the pad and the printed wire should not be greater than 0.3mm (for asymmetric pads), As shown in the above figure.

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8. How to install high-heat components and whether to consider a radiator
Make sure that the installation method of high-heat components is easy to operate and weld. In principle, when the heating density of components exceeds 0.4W/cm3, single the lead legs of the components and the components themselves are not sufficient for heat dissipation. Measures such as heat dissipation nets and bus bars should be adopted to improve the overcurrent performance.
The legs of the bus bar should be connected at multiple points, and wave soldering after riveting or direct wave soldering should be used as much as possible to facilitate the installation. Matching and soldering; for the use of longer bus bars, the thermal expansion coefficient of the heated bus bar and PCB should not match when the wave crest is used. The resulting PCB is deformed.
In order to ensure easy operation of tin lining, the width of the tin channel should not be greater than or equal to 2.0mm, and the distance between the edges of the tin channel should be greater than 1.5mm.