Nowadays we use many devices which are connected together with different cables (for example a computer with a smartphone). During design and manufacturing, our aim is to minimize the contact resistance. If we connect and disconnect these cables multiple times, the contact resistante of the connection will be higher, which can influence the operability as well. In my thesis work, I have designed and tested such surface modification methods which decrease the contact resistance of connectors. I give an overview of the most frequently applied metals used for electrical connections. I present the manufacturing process of the designed edge connector PCBs which I used for measurement. Then I describe the roughing surface treatments by laser and sandblasting; as well as the low resistance measurement with the 4 wire method.
The experiment was carried on the surfaces of a PCB edge connector designed for a given socket. I roughed the connection surface of the PCB and compared the contact resistance with a reference – a surface without modification. I examined the connectors’ contact resistances of two known surface roughing methods: laser roughing and sandblasting.
I tested four different surface roughness patterns created with UV-Nd:YAG laser (wavelength 355 μm): vertical lines, horisontal lines, 45° parallel lines and grid. The distance between the lines – line spacing – was 70 and 90 μm, respectively. The thickness of the FR4 boards were 2 mm with 35 μm copper layer. Two types of coatings were used: immersion silver and electroless nickel immersion gold (ENIG). The output power of the laser was 2,9 W, the frequency was 28 kHz and the impulse energy was 105 μJ. The contact resistances were almost the same like the reference indepentedtly from the coating type, the pattern and the line spacing either. For the sandblasting, aluminium-oxide with a granule diameter of 120 μm was used. The roughing pressure was 1 bar and the duration was 10 s. The contact resistances were successfully reduced by this method, independetly from the coating type. The reduction was 8-10 % compared to the reference.