TECHNET Archives

September 2009

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Wed, 30 Sep 2009 12:20:00 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (133 lines)
Most everyone who knows me realizes that I am a strong proponent of immersion silver surface finish for several reasons. Many of you may have heard me state the main reason but not believed what I had to say.  So I'll repeat it again; we use immersion silver surface finish as a solderability indicator that our PCB fabricator didn't have a problem with incomplete tin strip or leave a solder mask residue on the PCB features and they should be solderable.  For a several year period when fine pitch components were beginning to appear on products I was assigned to work for an extremely large PCB fabricator and we were being pushed by our assembly factory customers to provide a flatter surface PCB surface finish for fine pitch assembly.  Our logical choice was to use Imidazole OSP because we had up and running in the factory and our customers were using it for old technology wave solder product.  When we switched to Imidazole for fine pitch surface mount boards everything looked okay for a while be every now and then one of the assembly customers would complain that there were features on their boards that weren't solderable.  After a lot of evaluations it was realized that in any large fabrication operation processes don't run with 100% perfect yield.  Checking back on boards used for previous non-fine-pitch products we realized that the HASL boards being supplied to customers were solderable because every feature on the boards had solder on them.  The reason we knew that was because we did 100% inspection at the end of the HASL line and if we saw any features on an 18"x24" panel with exposed copper (it's amazing how easily a non-solder-coated copper feature on a panel with thousands of features can be detected with the naked eye) the panel was put back through the HASL machine again hoping that the cleaning or micro etch or hot air leveling fusing fluid or the hot molten solder would clean off or burn off any incomplete tin strip or solder mask residue and the feature would accept solder.  If it didn't the second time we'd run it a third time and a fourth or fifth time in necessary before we knew better and limited reruns to only three.  When we switched from HASL to Imidazole we no longer had the visual confirmation that all the surface mount features were free of incomplete tin strip or solder mask residue because those contaminates were so thin the features appeared to be copper and after Imidazole they still looked like copper.  During that time period we also participated on the five year NCMS PCB Surface Finishes and Pb-Free efforts looking at new surface finishes for fin-pitch and Pb-Free assembly. Yes there was lots of doubt that a surface finish better than HASL could be found.  ENIG looked like a better choice at that time (Black Pad issues weren't publically disclosed at that time) than immersion tin because evaluations showed immersion tin had shelve life issues and exposure to temperature and humidity degraded its solderability. We decided to run an evaluation using ENIG boards because we know it provided a flat surface and after ENIG plating we believed we could tell the difference between a gold colored ENIG pad and a copper pad that hadn't accepted ENIG plating.  At the time when the evaluation was being planed AlphaLevel immersion silver was being introduced so it was decided to include it along with ENIG.  The evaluation didn't reveal any obvious problems with either surface finish but on some of the environmentally stressed boards the solder didn't flow out to the full extend on some on the ENIG features.  All of our experience up to this point (i.e., HASL and OSP) was with solder joints made to copper not nickel.  After extensive internal evaluations was decided to use immersion silver surface finish.  The reasons were simple:

1. It provided a visual indication before boards were assembled that there were no non-immersion-silver plated copper features indicating that incomplete tin strip or solder mask residue wasn't there and the features should be solderable.

2. Solder joints were being made to copper not nickel.
3. No reliability issues were found in our extensive testing.
4. It worked.

Participation on the IPC-3-11g committee confirmed everything we had determined in our internal testing.  In my mind the decision we made to use immersion silver surface finish was the correct decision because in 12 years we have no documented reliability issues associated with the use of immersion silver surface finish.  Granted our products are only Class 2 telecommunications products but they are deployed throughout the world in all kinds of environments and now in the 3G & 4G wireless world were service providers have having to deploy more active electronics at the tops of towers rather than in base stations they are viewing the reliability of the products as Class 3.

As I'm sitting here at my desk typing the long email I look up every now and then and I see a picture hanging next to my monitor that I took on July 26, 2005.  It is a photograph of my grandson sitting in front of a TV in my son's house in Friendswood, TX.  He is pointing to a person on the TV who is the lead space shuttle robotics engineer standing up in the NASA JSC Mission Control who is talking to an astronaut during a space walk.  That person is his father (my son) and my grandson is saying "that's my dad and I want to be just like him".  My son has an ambition to some day be an astronaut and so does my grandson.  You might ask what does this have to do with immersion silver.  The answer is simple to me.  With my FMA and reliability experience associated with immersion silver I would feel more comfortable if my son or grandson every because astronaut knowing that they were in space vehicles with electronics that used immersion silver surface finish that other options like ENIG or immersion tin. 

My apology again for such a long response.


Regards,
George
George M. Wenger
Andrew Solutions
Senior Principal FMA/Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 (Office) (732) 309-8964 (cell)
[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Wednesday, September 30, 2009 11:32 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver for Class 3 Boards

Good point about the environmental issues.  There are also recommendations I have seen that state ImAg is primarily a solderable surface protectant, and not the best selection as a final surface finish that may be exposed in the application.  In that case, the usual recommendations (that I have seen) are ENIG or HASL.

Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.

-----Original Message-----
From: Thayer, Wayne - IIW [mailto:[log in to unmask]]
Sent: Wednesday, September 30, 2009 11:22 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Silver for Class 3 Boards

People panic about silver migration, which is not really an issue.

However, there apparently is a very serious problem that can occur on uncoated boards in high sulfur environments, where somehow the silver acts to catalytically cause the copper to redeposit in random directions.  Doesn't even need a voltage to cause this phenomenon!

A paper on this was brought up to this forum several months back.  If you search the archives on ImAg you should be able to find it.  The growths are nice black dendrites.

Wayne Thayer

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Harner, Chester
Sent: Wednesday, September 30, 2009 11:03 AM
To: [log in to unmask]
Subject: [TN] Immersion Silver for Class 3 Boards

The revised Immersion Silver IPC spec (4553A) indicates that Immersion
Silver is not recommended for Class 3 boards. There is no stated reason.
I have been looking into Immersion Silver for all the same reasons as
everyone else, to replace HASL for flatness etc.  It looked very good
until the Class 3 problem.



Does anyone know why IAg would not be recommended for Class 3 boards?



Chet Harner   Sr. Engineer   Crane Hydro-AirePO Box 7722 Burbank Ca -
91510  818-526-2600 x3557




--------------------------------------------------------------------------------
We value your opinion!  How may we serve you better?
Please click the survey link to tell us how we are doing:
http://www.craneae.com/ContactUs/VoiceofCustomer.aspx
Your feedback is of the utmost importance to us. Thank you for your time.
--------------------------------------------------------------------------------
Crane Aerospace & Electronics Confidentiality Statement:
The information contained in this email message may be privileged and is
confidential information intended only for the use of the recipient, or any
employee or agent responsible to deliver it to the intended recipient. Any
unauthorized use, distribution or copying of this information is strictly prohibited
and may be unlawful. If you have received this communication in error, please notify
the sender immediately and destroy the original message and all attachments from
your electronic files.
--------------------------------------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

This e-mail and any files transmitted with it may be proprietary and are intended solely for the use of the individual or entity to whom they are addressed. If you have received this e-mail in error please notify the sender.
Please note that any views or opinions presented in this e-mail are solely those of the author and do not necessarily represent those of ITT Corporation. The recipient should check this e-mail and any attachments for the presence of viruses. ITT accepts no liability for any damage caused by any virus transmitted by this e-mail.

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------

ATOM RSS1 RSS2