The automotive electronics market is the third largest application area of PCB after computers and communications. With the gradual evolution and development of automobiles from mechanical products in the traditional sense into high-tech products of intelligence, informatization and mechatronics, electronic technology has been widely used in automobiles, whether it is engine system, chassis system, Electronic products are used in safety systems, information systems, and in-vehicle environment systems without exception. Among the key application objects of PCB today, automotive PCB occupies an important position. However, due to the special working environment, safety and high current requirements of automobiles, it has higher requirements on PCB reliability and environmental adaptability.
How to test the quality of automotive pcb?
1. High and low temperature cycle test. Automotive PCBs used in power control systems and brake control systems require higher reliability in design and process. For example, automotive control systems usually require 500 high and low temperature cycles, and individual key components even require up to 2000 high and low temperature cycles.
A. High and low temperature cycle test conditions and requirements. Low temperature to high temperature: -40c-125℃, conversion time: 10s, duration after reaching the highest (low) temperature: 15min, interconnect resistance change rate <10% (some customers require <5%).
B. Improvement direction. The cracks appearing in slices after high and low temperature have a great relationship with the Tg value of the plate, the quality of the drilling, and the concave corrosion before PTH. To reduce the degree of 2-axis expansion of the plate thickness, it is necessary to select materials well. ,
2. Drilling. By using three different types of backing boards (phenolic backing board, wooden backing board and melamine backing board) to conduct drilling experiments, the sludge on the hole wall was observed by SEM after drilling. When the wooden backing plate is used, there is more sludge on one side of the hole wall and less sludge on the other side; when the melamine backing plate is used, the drilling sludge is evenly distributed on the hole wall, and the amount of sludge is relatively small.
3. Etching. With different etchback methods, the amount of etchback on the hole wall will be somewhat different. How to effectively remove epoxy drilling contamination, ensure that the hole wall roughness meets the requirements and reduce the wicking effect is a headache for many pcb manufacturers. Due to the large roughness of the hole wall, it will lead to blowing holes during welding and fracture of the coating during high and low temperature cycles; the large wicking effect may cause electromigration between holes and form a short circuit; if the control of the amount of concave corrosion is relatively small, cracks may appear at the joint after high and low temperature cycling.
4. Electromigration problem: Under the condition of high temperature and high humidity environment, due to the existence of the primary battery phenomenon, the PCB may experience electromigration phenomenon (also known as electro corrosion), which will cause the insulation resistance between insulators to decrease with time, even Secondary hazards such as short circuit and parts heating and fire occur. Therefore, car manufacturers pay more and more attention to this aspect.
