Hello George,
I'm curious, have you performed conformal coating on immersion silver surface finish to improve reliability? Thanks a lot.
Best Regards
Charming Chan
-----Original Message-----
From: Wenger, George M. <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, Oct 1, 2009 1:20 am
Subject: Re: [TN] Immersion Silver for Class 3 Boards
Most everyone who knows me realizes that I am a strong proponent of immersion
ilver surface finish for several reasons. Many of you may have heard me state
he main reason but not believed what I had to say. So I'll repeat it again; we
se immersion silver surface finish as a solderability indicator that our PCB
abricator didn't have a problem with incomplete tin strip or leave a solder
ask residue on the PCB features and they should be solderable. For a several
ear period when fine pitch components were beginning to appear on products I
as assigned to work for an extremely large PCB fabricator and we were being
ushed by our assembly factory customers to provide a flatter surface PCB
urface finish for fine pitch assembly. Our logical choice was to use Imidazole
SP because we had up and running in the factory and our customers were using it
or old technology wave solder product. When we switched to Imidazole for fine
itch surface mount boards everything looked okay for a while be every now and
hen one of the assembly customers would complain that there were features on
heir boards that weren't solderable. After a lot of evaluations it was
ealized that in any large fabrication operation processes don't run with 100%
erfect yield. Checking back on boards used for previous non-fine-pitch
roducts we realized that the HASL boards being supplied to customers were
olderable because every feature on the boards had solder on them. The reason
e knew that was because we did 100% inspection at the end of the HASL line and
f we saw any features on an 18"x24" panel with exposed copper (it's amazing how
asily a non-solder-coated copper feature on a panel with thousands of features
an be detected with the naked eye) the panel was put back through the HASL
achine again hoping that the cleaning or micro etch or hot air leveling fusing
luid or the hot molten solder would clean off or burn off any incomplete tin
trip or solder mask residue and the feature would accept solder. If it didn't
he second time we'd run it a third time and a fourth or fifth time in necessary
efore we knew better and limited reruns to only three. When we switched from
ASL to Imidazole we no longer had the visual confirmation that all the surface
ount features were free of incomplete tin strip or solder mask residue because
hose contaminates were so thin the features appeared to be copper and after
midazole they still looked like copper. During that time period we also
articipated on the five year NCMS PCB Surface Finishes and Pb-Free efforts
ooking at new surface finishes for fin-pitch and Pb-Free assembly. Yes there
as lots of doubt that a surface finish better than HASL could be found. ENIG
ooked like a better choice at that time (Black Pad issues weren't publically
isclosed at that time) than immersion tin because evaluations showed immersion
in had shelve life issues and exposure to temperature and humidity degraded its
olderability. We decided to run an evaluation using ENIG boards because we know
t provided a flat surface and after ENIG plating we believed we could tell the
ifference between a gold colored ENIG pad and a copper pad that hadn't accepted
NIG plating. At the time when the evaluation was being planed AlphaLevel
mmersion silver was being introduced so it was decided to include it along with
NIG. The evaluation didn't reveal any obvious problems with either surface
inish but on some of the environmentally stressed boards the solder didn't flow
ut to the full extend on some on the ENIG features. All of our experience up
o this point (i.e., HASL and OSP) was with solder joints made to copper not
ickel. After extensive internal evaluations was decided to use immersion
ilver surface finish. The reasons were simple:
1. It provided a visual indication before boards were assembled that there were
o non-immersion-silver plated copper features indicating that incomplete tin
trip or solder mask residue wasn't there and the features should be solderable.
2. Solder joints were being made to copper not nickel.
. No reliability issues were found in our extensive testing.
. It worked.
Participation on the IPC-3-11g committee confirmed everything we had determined
n our internal testing. In my mind the decision we made to use immersion
ilver surface finish was the correct decision because in 12 years we have no
ocumented reliability issues associated with the use of immersion silver
urface finish. Granted our products are only Class 2 telecommunications
roducts but they are deployed throughout the world in all kinds of environments
nd now in the 3G & 4G wireless world were service providers have having to
eploy more active electronics at the tops of towers rather than in base
tations 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
hen and I see a picture hanging next to my monitor that I took on July 26,
005. It is a photograph of my grandson sitting in front of a TV in my son's
ouse in Friendswood, TX. He is pointing to a person on the TV who is the lead
pace shuttle robotics engineer standing up in the NASA JSC Mission Control who
s talking to an astronaut during a space walk. That person is his father (my
on) and my grandson is saying "that's my dad and I want to be just like him".
y son has an ambition to some day be an astronaut and so does my grandson. You
ight ask what does this have to do with immersion silver. The answer is simple
o me. With my FMA and reliability experience associated with immersion silver
would feel more comfortable if my son or grandson every because astronaut
nowing that they were in space vehicles with electronics that used immersion
ilver surface finish that other options like ENIG or immersion tin.
My apology again for such a long response.
egards,
eorge
eorge M. Wenger
ndrew Solutions
enior Principal FMA/Reliability Engineer
0 Technology Drive, Warren, NJ 07059
908) 546-4531 (Office) (732) 309-8964 (cell)
[log in to unmask]
-----Original Message-----
rom: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
ent: Wednesday, September 30, 2009 11:32 AM
o: [log in to unmask]
ubject: Re: [TN] Immersion Silver for Class 3 Boards
Good point about the environmental issues. There are also recommendations I
ave seen that state ImAg is primarily a solderable surface protectant, and not
he best selection as a final surface finish that may be exposed in the
pplication. In that case, the usual recommendations (that I have seen) are
NIG or HASL.
Kevin Glidden
anufacturing Engineer
uminescent Systems Inc.
-----Original Message-----
rom: Thayer, Wayne - IIW [mailto:[log in to unmask]]
ent: Wednesday, September 30, 2009 11:22 AM
o: [log in to unmask]
ubject: 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
oards in high sulfur environments, where somehow the silver acts to
atalytically cause the copper to redeposit in random directions. Doesn't even
eed a voltage to cause this phenomenon!
A paper on this was brought up to this forum several months back. If you search
he archives on ImAg you should be able to find it. The growths are nice black
endrites.
Wayne Thayer
-----Original Message-----
rom: TechNet [mailto:[log in to unmask]] On Behalf Of Harner, Chester
ent: Wednesday, September 30, 2009 11:03 AM
o: [log in to unmask]
ubject: [TN] Immersion Silver for Class 3 Boards
The revised Immersion Silver IPC spec (4553A) indicates that Immersion
ilver is not recommended for Class 3 boards. There is no stated reason.
have been looking into Immersion Silver for all the same reasons as
veryone else, to replace HASL for flatness etc. It looked very good
ntil 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 -
1510 818-526-2600 x3557
-------------------------------------------------------------------------------
e value your opinion! How may we serve you better?
lease click the survey link to tell us how we are doing:
ttp://www.craneae.com/ContactUs/VoiceofCustomer.aspx
our feedback is of the utmost importance to us. Thank you for your time.
-------------------------------------------------------------------------------
rane Aerospace & Electronics Confidentiality Statement:
he information contained in this email message may be privileged and is
onfidential information intended only for the use of the recipient, or any
mployee or agent responsible to deliver it to the intended recipient. Any
nauthorized use, distribution or copying of this information is strictly
rohibited
nd may be unlawful. If you have received this communication in error, please
otify
he sender immediately and destroy the original message and all attachments from
our electronic files.
-------------------------------------------------------------------------------
---------------------------------------------------
echnet Mail List provided as a service by IPC using LISTSERV 15.0
o unsubscribe, send a message to [log in to unmask] with following text in
he BODY (NOT the subject field): SIGNOFF Technet
o temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
o receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
earch the archives of previous posts at: http://listserv.ipc.org/archives
lease visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
dditional information, or contact Keach Sasamori at [log in to unmask] or
47-615-7100 ext.2815
----------------------------------------------------
This e-mail and any files transmitted with it may be proprietary and are
ntended solely for the use of the individual or entity to whom they are
ddressed. If you have received this e-mail in error please notify the sender.
lease note that any views or opinions presented in this e-mail are solely those
f the author and do not necessarily represent those of ITT Corporation. The
ecipient should check this e-mail and any attachments for the presence of
iruses. ITT accepts no liability for any damage caused by any virus transmitted
y this e-mail.
---------------------------------------------------
echnet Mail List provided as a service by IPC using LISTSERV 15.0
o unsubscribe, send a message to [log in to unmask] with following text in
he BODY (NOT the subject field): SIGNOFF Technet
o temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
o receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
earch the archives of previous posts at: http://listserv.ipc.org/archives
lease visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
dditional information, or contact Keach Sasamori at [log in to unmask] or
47-615-7100 ext.2815
----------------------------------------------------
---------------------------------------------------
echnet Mail List provided as a service by IPC using LISTSERV 15.0
o unsubscribe, send a message to [log in to unmask] with following text in
he BODY (NOT the subject field): SIGNOFF Technet
o temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
o receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
earch the archives of previous posts at: http://listserv.ipc.org/archives
lease visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
dditional information, or contact Keach Sasamori at [log in to unmask] or
47-615-7100 ext.2815
----------------------------------------------------
---------------------------------------------------
echnet Mail List provided as a service by IPC using LISTSERV 15.0
o unsubscribe, send a message to [log in to unmask] with following text in
he BODY (NOT the subject field): SIGNOFF Technet
o temporarily halt or (re-start) delivery of Technet send e-mail to
[log in to unmask]: SET Technet NOMAIL or (MAIL)
o receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
earch the archives of previous posts at: http://listserv.ipc.org/archives
lease visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
dditional information, or contact Keach Sasamori at [log in to unmask] or
47-615-7100 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
-----------------------------------------------------
|
