Pcb Surface Finishes
An obstacle in the selection of the proper floor end is the truth that this choice directly impacts many practical teams inside a company. For example if the procurement group is liable for choosing the finish they will doubtless proceed with whatever is lowest price on the PCB degree.
There are many surface finishes presently sharing the market with no clear winner coming ahead. Each floor end has attributes that make it enticing for certain functions; nonetheless, this also implies that essential tradeoffs are being made.
This paper will present each finish option with the important thing product concerns in mind. Thankfully, by way of excessive research and compiled information, immersion gold chemistry suppliers and printed circuit board producers have improvised and improved their supplies and processes. Parameters could be WHERE set to minimize or even eliminate occurrences of black pad points related to the immersion gold process by avoiding essentially the most well documented causes. Years in the past, when Epec began to make use of the electroless nickel immersion gold course of.
This concern wasn’t seen at the time, as it's not evident on the bare board, but acquired the complaint from meeting because it was later recognized on accomplished assemblies. In the PCB business ENEPIG is also called the universal finish as it is relevant to a variety of boards, particularly the fashionable, highly advanced ones with a number of types of surface packages. Similar to the ENIG surface finish, ENEPIG also presents a superb flat surface, is easy to process, and has no poisonous results on the pores and skin.
In mixed technology i.e. when RF and digital circuits are concerned, choosing direct gold floor finish will lead to meeting associated issues. Whereas, ENEPIG is appropriate with combined expertise and the assorted assembly processes. Black pad stays a potential downside with ENIG when the gold plating course of isn't well controlled. Black pad outcomes from dissolution of the surface of the Ni layer upon submersion within the acidic gold plating bathtub.
ImAg is a skinny film of silver (typically 6-12 µ”) deposited directly on copper. In 2003, before RoHS took impact, the market share of ImAg as a floor finish was under 2%. The deposition gear may be expensive but the via-put is high enough to deliver the fee per sqft to just above that of OSP. The popularity of this finish acquired a boost in 2006 when Underwriters Laboratory reconfirmed ImAg as a suitable end after performing temperature/humidity/bias testing with favorable outcomes .
A PCB part engineer would possibly choose the end that's easiest for the PCB supplier to provide with high yield. The meeting or high quality engineer would doubtless be most drawn to the finish that provides the largest course of window for assembly and test. The sustaining engineer and reliability engineer have an interest in the finish that gives the most strong finish product. In the tip, the best surface finish in your application is the one that considers the impression to all features and provides the bottom general cost.
When wetted with solder, the gold rapidly dissolves and the tin is left to react with the phosphorous wealthy layer. The resulting poor bond power can cause failure within the subject when the solder joint is stressed. This figure also shows the preferential etching of the nickel along the grain boundaries, as noticed when the top gold layer is stripped away.