PCB News - Car PCB design specification reference

PCB design specification reference for automotive products

Design concept: In the circuit and PCB design stage, it needs to be combined with the production process to avoid the inability to process or increase the processing difficulty and cost due to irregular design. The most important thing is that if the PCB needs to be redesigned or changed greatly, this time The various reliability tests done in the trial production are meaningless and cannot reflect the production requirements of the final product; Design requirements:

1. Each component must have a detailed specification. When designing the circuit, it is necessary to check whether the device meets the requirements of the vehicle regulations and whether there is a lead-free model. When designing the PCB, it is necessary to check whether the soldering temperature curve meets the production requirements, if not. Need to find substitutes of the same specification. The pad size and component packaging need to be made in accordance with the size recommended by the component manufacturer to avoid processing difficulties caused by non-standard design;

2. The pad size of the chip resistors and capacitors is increased accordingly on the basis of the standard. For the specific size, please refer to the document requirements. The purpose is to ensure sufficient soldering. The requirements on the car are higher and to avoid long-term vibrations that may lead to desoldering and false soldering. ;

3. The vias and pads of the plug-in components need to be uniformly required and designed in strict accordance with the manufacturer's specification. If there is no relevant content in the specification, the manufacturer must be required to provide a written reference size;

4. SMD aluminum electrolytic capacitors are placed on the side that is only reflow soldered once. If reflow soldering twice will cause damage to aluminum electrolysis;

5. The gap between the components of the reflow soldering process: ≧0.4mm, calculated as the outermost size;

6. The gap between the plug-in component and the patch component: ≧3mm, which is convenient for manual repair soldering or partial reflow soldering;

7. Large and heavy components are placed on the side that is only reflow soldered once to prevent falling off and false soldering caused by secondary reflow soldering;

8. No components can be placed within 5mm of the processing side, and no test points can be placed within 3mm. The wiring can be routed but a protective white glaze should be applied to the wiring to avoid scratching the wiring during processing;

9. The height of the component needs to be determined according to the processing machine (mounter/reflow soldering machine) to determine the highest range, to avoid components that are too high to be processed;

10. The components within 10-20mm close to the side that will flow solder are placed as far as possible to avoid insufficient soldering due to too dense components;

11. Do not close the components of large size together, which will cause inconvenience in repairing, and the uneven heat of reflow soldering will cause poor soldering;

12. The plug-in components should be placed on the same side as much as possible to facilitate processing;

13. Polarized components (aluminum capacitors/tantalum capacitors/diodes, etc.) should be arranged in the same direction as far as possible to facilitate visual inspection. If they cannot be placed in this way due to performance considerations, they must also be locally aligned;

14. The component tag must be clear, the writing specifications of each board must be consistent, and the same type of components must be consistent to facilitate repair and testing;

15. The pad for ICT testing is 0.99mm, and each network needs to have test points, which need to be added during circuit design. If a certain part is indeed too dense for components to place test points, this requires circuit designers and PCB designers discuss together and decide which ones are necessary, and cannot modify them at will;

16. Components that need to be fixed with glue must be marked during circuit design, so that PCB designers and factory processing personnel can consider countermeasures in advance when designing and processing;

17. The welding surface of the hand-inserted component needs to be marked in white, so that the operator can understand that welding can only be done in this area, and it is also convenient for visual inspection personnel to quickly find the location to be inspected;

18. The same component should be placed on the same side as far as possible. For example, if you need 10 components of this type, don't put 9 on the A side, and 1 on the B side, which will increase the burden on the patch ingredients;

19. Do not place components within 4mm of the edge of the V-CUT;

20. The selection requirements of the connector: easy to insert, but also easy to pull;

add:

1. The thickness of the copper foil of the PCB board is 35um. When designing the wiring, you must consider the size of the line overcurrent. The principle is to design according to the relationship of 1:1, that is, the current 1A line width is 1mm. In order to ensure the processing, the minimum line width is set as 0.2mm, the designer needs to refer to the current consumption document to ensure that the wiring can be routed above the regulations when routing the wires, ordinary signal wire vias are 0.4mm, and the vias with larger current can be designed to be 0.7mm, and you can consider placing multiple vias. Hole, depending on the current.

2. For the ground wire layout of the AUDIO part, it is tentatively determined to be the 1-point grounding method. Although the 4-layer board is used for wiring, the second layer is used for the power supply, and the third layer is used for the ground wire, but the ground wire of the radio part/attack part The latter point needs to be processed separately and connected to the entrance of the general ground wire, and the digital and analog ground wires such as DSP/CPU are separated to eliminate the low-level method of randomly punching the ground wire;

3. For the ground wire layout of the display part, it is necessary to distinguish between the digital and analog ground wires of the driver IC, otherwise it will cause image interference. Pay attention to the distance of the high-voltage wiring to prevent high-voltage sparking. Pay attention to the ground wire shielding of the signal wire to reduce EMC interference. 4-layer board wiring, layer 2 power supply, layer 3 ground wire, and digital and analog ground wires are separated and grounded in a large area on layer 3;

4. For the front panel, because the Bluetooth is a separate module, a 2-layer PCB board can be used for wiring, as long as the digital and analog grounds are distinguished, and the large-area grounding method is adopted;

5. For the connecting board, since there are only analog signals such as power supply, it is enough to distinguish between the attack and the other parts. The 4-layer board is used for wiring, and the socket part is shielded by copper to reduce EMC;

6. The ESD tubes and capacitors used for port protection should be as close to the port as possible, and the protection part of the connector part should be as close as possible to the connector pins;

7. When the P board and the shell are grounded, it is necessary to consider how to ground adequately. The design of the screw hole and the design of the ground wire should be considered. The AUDIO and DISPLAY parts need to be carefully considered;

8. The filter capacitor of the component power supply part must be as close as possible to the pin;

9. The thickness of all P boards is above 1.5mm, including small module boards;

10. The wiring of the 2-layer board should not be less than 0.2mm, the line spacing should not be less than 0.25mm, and the copper laying spacing should not be less than 0.3mm;

11. The wiring of the power strip and the external interface needs to have test points to facilitate the thimble operation during the simulation inspection of the workshop;