Surface Finish Selection
Surface finish selection on PCBs is the most important step for PCB fabrication since it directly influences process yields, rework numbers, field failure rate, test capability, scrap rate and cost. All the important considerations about assembly must be taken into surface finish selection in order to ensure the high quality and performance of end products.
In PCB assembly process, people with different positions have different opinions on how to select surface finish. Figure 6 shows some ideas:
Apparently, people with different positions have different selection standards. No matter what type is selected, it only caters to the requirements and convenience of people with few considerations about the quality, performance and reliability of PCBs and PCB assembly.
So, as for the type of surface finish selection, an optimal type must be selected and numerous functions can be accomplished. Each type of surface finish has its own advantages and disadvantages. But don’t worry. There are some engineering tricks as the solutions to the problems caused by cons of surface finish. For example, as for the disadvantage that OSP has lower wetting force, some solutions are available such as changing board solderability plating or wave solder alloy, increasing top-side preheat etc. The key point is that all the possible elements must be considered in order to obtain ideal performance.
Nowadays, environment issues have become increasingly important in the electronic fields. In order to restrain the generated hazardous substances, RoHS is published by EU. RoHS, also known as Lead-Free, stands for Restriction of Hazardous Substances. RoHS, also known as Directive 2002/95/EC, originated in the European Union and restricts the use of six hazardous materials found in electrical and electronic products. All applicable products in the EU market after July 1, 2006 must pass RoHS compliance. RoHS impacts the entire electronics industry and many electrical products as well. So, surface finishes with lead-free solder will have more followers in the future.