Bob, Richard,
I can't help but jump in again with a comment.
The primary surface finish we use for wireless telecommunications equipment is immersion silver. We do use some ENIG on legacy products and see no reason to switch especially when we haven't experienced any problems. My first experience with ENIG problems was when I was evaluating a new Ethernet PCMCIA card that used ENIG back in the mid-90's. The fine pitch Motorola and Altera BGAs on this product had brittle interface solder joint cracks at the BGA ball/PCB interface, especially at outer corners or at the edge of internal die. We know the problem wasn't the quality of the Motorola or Altera BGAs and we also couldn't find anything wrong with the fabrication of the ENIG boards we were receiving from our board supplier. The real problem was that the solder (SnPb) interconnection to the nickel plating of the ENIG surface finish couldn't withstand the stress the product would see during actual use.
You'll notice I didn't use that name with initials B.P. because I've never liken the name because it describes what one sees when there is a failure and not the actual failure mode. The real problem I have with ENIG is that even after the many years of evaluations by lots of talented people there really hasn't been an actual root cause defined other than something in the plating process was not controlled. To avoid ENIG problems everyone agrees that you should use good board fabricating and plating shops and you should control everything in the plating process. What really causes the ENIG problem? Is it the P level in the Ni plating? Is it the concentration of materials and additives in the plating baths? Is it the length of time between Ni and Au plating? Is it that you need to minimize the time in the Au bath to minimize attack on the Ni? If we really knew what the root cause was and could reproduce the failures at will then we would be a lot closer to understanding what the problem is then we are right now. All we really know is that we need to work with good board shops and they have to control and monitor everything in their ENIG plating line.
My experience in failure analysis and reliability leads me to the conclusion that we should be using processes and chemistries that don't require a lot of controls because sooner or later there will be an occasion where someone gets lazy or forgets a process control check and all of a sudden there is an issue. And even worse yet those occasions seem to happen at the worse times (e.g., introduction of a new product or ramp-up in production volume). We will continue to use ENIG on our legacy products and I have to assume that those in the electronics industry who have been using ENIG successfully will also continue to use what has worked for them. However, when product designs change (i.e., get more complicated and more susceptible to handling and use stress) or competition requires cost reductions to existing products ENIG problems could occur and when they do the question will come up again what surface finish should I switch to or how can I control my ENIG process better.
Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, August 04, 2011 9:28 AM
To: [log in to unmask]
Subject: Re: [TN] Steps to take to prevent ENIG issues
Thanks, Bob. I cannot switch suppliers without a major re-qualification effort for this client. So I am trying to find ways of checking the PWBs as they come in so any issues are detected PRIOR to assembly, not during or after. I believe the fabricator they chose is very capable, but they want to know how to catch anything if issues arise.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Thursday, August 04, 2011 8:14 AM
To: [log in to unmask]
Subject: Re: [TN] Steps to take to prevent ENIG issues
Richard,
Have listened to all here who commented. Bay Area Circuits in Redwood City CA does our boards. They sub out the ENIG as they didn't do enough of it to stay on top of the potential problems with it (too expensive to maintain an ENIG line unless you have the volume, apparently). We are totally happy with their ENIG boards (we use BGAs and QFNs).
Bob Landman
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, August 03, 2011 11:17 AM
To: [log in to unmask]
Subject: [TN] Steps to take to prevent ENIG issues
I have a client who is switching PWB fabricators for ENIG finishes. They are fully aware of ENIG issues such as Black Pad, Brittle Nickel, etc., and want to know whatever steps can be taken to prevent ENIG PWBs from reaching production with these issues.
Does anyone have any suggestions?
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