Due to increasing electronization of automotive vehicles, automotive PCBs have been widely applied in automotive electronics including power control system, safety control system, communication entertainment etc. The same with standard PCBs, automotive PCBs is mainly a combination of PCB solder mask and CCL (Copper Clad Laminate) which play a crucial role in support, interconnection, insulation and protection.
As an essential part contributing to automotive PCB, solder resist ink is used to insulate and protect traces from being soldered or oxidized. In addition, solder resist ink is helpful in stopping solder paste from sticking during the process of reflow soldering or wave soldering. Because of extremely high requirement on safety of automotive vehicles, which is a special attribute, solder mask ink applied on automotive PCBs is required to maintain stable in its performance in more than one decade’s application process in order to stop breakdown from occurring.
In a word, solder mask ink on automotive PCB not only has to meet general demands laid by ordinary PCBs but also has to meet specific demands in accordance with particularity of automotive industry.
General Demands Solder Mask Ink on Automotive PCB Has to Meet
General demands solder mask ink on automotive PCB has to meet include the following aspects:
a. Automotive PCB solder resist ink should be compatible with IPC-840E test requirement and UL requirement.
b. Automotive PCB solder mask ink has to be compatible with the requirement for hazardous substances control such as REACH, ROHS, Halogen Free etc.
c. Automotive PCB solder resist ink has to be compatible with the requirement laid by later steps during PCB manufacturing process. For example, solder resist ink has to withstand the effect of surface finish coating like HASL, ENIG, OSP etc.
d. Automotive PCB solder mask ink has to be capable of withstanding wave soldering and reflow soldering for three times.
Special Demands Solder Mask Ink on Automotive PCB Has to Meet
During decades’ application of automotive vehicles, solder mask ink on automotive PCB has to carry out significant functions like insulation and protection, which calls for solder mask ink to maintain durable for a long time. As a result, high weatherability counts as far as solder mask ink on automotive PCB is concerned.
Specifically, high weatherability of solder mask ink on automotive PCB refers to the fact that it has to pass high-low temperature cycle aging resistance test, high-temperature aging resistance test and electromigration aging resistance test.
a. High-Low Temperature Cycle Aging Resistance Test
This test aims to testify whether solder resist ink on automotive PCB is capable of keeping its stability in the alternating environment of extreme coldness and extreme heat. The performance of solder mask ink on automotive PCB relies on the stability time and cycle time under high-low temperatures. The optimal ink going through this test is still capable of meeting the demands even if its aging is fastened in extremely high-temperature, extremely high-humidity and extremely cold environment.
b. High-Temperature Aging Resistance Test
High-temperature aging resistance test aims to observe the performance change of solder mask ink on automotive PCB and its performance depends on the temperature and lasting time. The optimal ink going through this test fails to suffer from bubbles, wrinkles, cracks or peeling.
c. Electromigration Aging Resistance Test
Electromigration aging resistance test aims to testify whether the migration of metal ions will lead shorts and reduced insulation to occur under the effect of electric field or in high-temperature and high-humidity environment.