Getting the Right Finish, Before You Start

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If you are a fan of John Wooden, the celebrated UCLA coach, you will know that he had more than his share of clever sayings. My husband, who played basketball all his life, and who went to college on a full-ride scholarship—nearly worships Coach Wooden. For this reason, I have heard many of these wise and witty Wooden-isms over the years. One that comes to mind is: “Be quick, but don’t hurry.” With the speed of advancing technologies, we all have to be quick, but we cannot afford to hurry—or be hasty—putting revenue and market share opportunities at stake.

In regards to RF and microwave printed circuit boards, there seems to be some confusion about PCB finishes and their affect on the high performance requirements of these applications. Too often, when considering the available finishes and the potential impact they have on performance, many engineers become both quick and (unwittingly) hasty when they make finish choices based on information, which is conflicted, at best.

I think it’s time to clear up some of these issues, so I am going to spend the next few blog posts talking about these issues. Hopefully, by the time I’m through you will have a much clearer understanding of finishes and which to choose for your product, before you start! I will be drawing from our real-world experiences, as well as looking to experts in the substrate and RF design industries.

Today, I am just going to cover the major available finishes, and which ones seem to be preferred by those with high speed applications:

  • Tin (Lead free)
  • HASL (Hot Air Solder Leveling) Tin/Lead 63/37
  • ENIG (Electroless Nickel Immersion Gold)
  • ENEPIG (Electroless Nickel/Electroless Palladium/Immersion Gold)
  • Hard Gold
  • Soft Gold
  • Immersion Tin
  • Immersion Silver

In high-speed applications, the prevailing wisdom suggests ENIG, ENEPIG, hard gold, soft gold and immersion silver are the best choices. Gold is a natural choice due to the fact that it does not oxidize and that it is wire-bondable. Immersion silver is gaining some traction due to the excellent conductivity, but it oxidizes and it is not wire-bondable, which keeps many from choosing this option.

Unfortunately, I must leave us barely posed in the starting blocks, in regards to finishes! In two weeks, however, I will sound the starting shot, and we will be off to the races. I will discuss each finish in more detail with the pros and cons of each.

If you have specific questions you would like to submit about this subject, please post them here in the comment section or email me at: [email protected].

I’m looking forward to tackling this complex and critical subject together!

 

–Judy