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PCB Surface finish

Steve Thomas

#29198

PCB Surface finish | 22 June, 2004

A very quick survey regarding PCB finishes for a lead-free process. What is the most popular PCB finish for lead-free soldering ? Who drives the selection of the finish, assembler or designer ? Are tin whiskers an issue for anyone ?

I'm coming at this issue from a design angle so :

Are there any design releated issues associated with a lead-free process?

Are all of the PCB finishes suitable for lead-free also OK for Sn/Pb soldering ?

TIA Steve

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#29304

PCB Surface finish | 28 June, 2004

Q1: What is the most popular PCB finish for lead-free soldering ? A1: We'd guess ENIG

Q2: Who drives the selection of the finish, assembler or designer ? A2: A tight circle of recrimination, blame letting, and other human ills that is primarily driven by design and purchasing, leaving the poor saps in production to deal with decisions driven by who last took someone to lunch.

Q3: Are tin whiskers an issue for anyone ? A3: No, we will use tin lead until pry it out of my cold dead fingers.

Q4: Are there any design releated issues associated with a lead-free process? A4: Stay away from bismuth.

Q5: Are all of the PCB finishes suitable for lead-free also OK for Sn/Pb soldering ? A5: We think so

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blnorman

#29356

PCB Surface finish | 2 July, 2004

We looked into OSP for lead free. OSP is less costly than ENGI.

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KEN

#29368

PCB Surface finish | 3 July, 2004

Steve, the web will not do your needs justice. I would suggest reading everything you can get your hands on. There is much to be learned that has already been published...and even more that has not.

There are so many trade-offs with surface finish selections...

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indy

#29370

PCB Surface finish | 4 July, 2004

What is the most popular PCB finish for lead-free soldering ? We are using ENIG and trying out Paladium-Silver.

Are tin whiskers an issue for anyone ?

tin whiskering becomes a big issue if you have any military company as your client. They still prefer to use Sn/Pb.

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#29374

PCB Surface finish | 5 July, 2004

Dave,

I'm going to disagree with you on the ENIG, it's my 3rd choice only just beating out OSP for that 4th spot. 1. Immersion Silver - cheaper than ENIG, as flat and no issues with Brittle interface (black pad) or Gold Embrittlement) Longer shelf life and all that jazz, it's lovely stuff to work with!!!!!!!!!! 2. Immersion Tin. So far I don't think I've heard of anyone having a problem with Tin Whiskering in real life, but I could be and probably am wrong. I run a number of boards on Tin and it stands up well, shelf life is ok if yoru doign soem decent volumes and it's fine for wave solder. 3. ENIG - only due to the flatness side of things and that I had real bad issues with OSP's a few years ago, yes yes they have moved on but you know I just can't shake the feeling that at the higher temps there are going to be processign issues and oxidised copper all over the place. 4. OSP if I really really ever had to use it because someone had a gun to my head. of course don't forget you can get a Pb-Free HASL finish, soem platers are running the Nehon Superior in their HASL baths and it's really a nice finish and flows well. At the moment my shop is probably 40% HASL, 40% Silver, 18% gold and the rest Tin. If people haven't looked at the Silver yet I'd urge them to do it. Obviously as I found out to my cost a few months back you do have to watch out for the peelable mask with Silver... thanks again for that Dave.

cheers for now

John

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indy

#29382

PCB Surface finish | 6 July, 2004

john, Immerson Silver is probably a good choice. What is your opinion abt Palladium silver. Does presence of Palladium affect the reliability of the pcb surface finish

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#29394

PCB Surface finish | 6 July, 2004

Thanks to all who responded, very helpful.

The responses have confirmed my suspicions, namely that there is no real favourite when it comes to PCB surface finishes all have good and bad points. I'll go with the one my assembler suggests then I can blame him for any problems, right! :o)

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#29404

PCB Surface finish | 7 July, 2004

Indy,

I'm not sure to be honest, I think as long as you have confidence the silver layer is good then in theory it should be ok.

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