Hi George! Very nice examples and great info! I'll be putting those
pictures in my photo gallery collection as tarnish examples. Someone at
one of the IPC meetings made the statement that "Immersion silver surface
finishes try to provide a visual appearance of how their solderability
might be changing over time" - I thought that statement emphasized one of
immersion silver's positive attributes in comparison to other pwb surface
finishes we use as an industry.
Dave
"Wenger, George M." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/10/2011 09:40 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Wenger, George M." <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] IPC-4553
Kevin,
I read your Tuesday, Feb 8th posting and was going to respond but I got
tied up with critical issues that I couldn't put off. Now that things
have settled down I figured it would still be good to respond especially
after reading the answers Dave and Richard provided which I agree with.
Dave,
I totally agree with your Immersion Silver Visual Appearance Rule of
Thumb. When I read Kevin's TN post I decided to go through my desk and
find some really old immersion silver plated boards I know I had saved. In
the attached PDF file (I've copied Steve in hopes he can post the file on
his site) are photographs of National Center for Manufacturing Science
(NCMS) test boards that were plated with immersion silver boards during
Week 04 of 1997. Jim Reed sent me these two boards and I've had these two
test boards in my desk in a non-sealed plastic bag for 15 years. When I
opened the bag it was obvious that the board that the immersion silver
plated pads on the top board had a yellowish-brown tint compared to the
board that was at the bottom. I haven't done any SEM/EDX analysis on
these two boards but we have done lots of analysis on other immersion
silver boards with this type of discoloration and know this is mild
tarnish.
There are also photographs of the electromigration boards that were plated
with immersion silver during Week 22 of 2003 as part of the joint work
between UL and IPC 3-11g committee. I had a few of these board wrapped in
aluminum foil in my desk for the past 7 1/2 years. As you know, immersion
silver has been our surface finish of choice since 1997 even before UL
changed their silver testing requirements. I had opened the 'A' board
several times to show visitors to our Lab and as a result the bottom edge
of the aluminum foil was torn leaving the bottom edge of the board exposed
to our Lab environment. You can see some discoloration on the pads at the
bottom edge of the board. Nevertheless I am sure they are solderable.
In the many years we've been using immersion silver we have not
experienced any reliability issue associated with the immersion silver
surface finish. Our products aren't deployed in space but they are
deployed worldwide in outdoor environments even in countries with known
air pollution issues. We do get failed products returned for repair or
replacement but there hasn't been a case where a product has failed due to
the immersion silver surface finish used on PCBAs.
We don't have a visual appearance guideline but I'm often asked for
questions about discolored or stained boards. The following are some of
those questions; "We found some 2 or 3 year old boards in our warehouse
and we'd like to use them for production but they are discolored. Can we
use them for production?" or "A leak developed in the roof of our
storeroom and a group of boards got wet and after we dried them they look
a little discolored and there is some staining. Can we use them for
production?." Being and FMA / Reliability engineer my usual answer is to
take a small sample of the boards and do your normal solder assembly (you
know me "Nothing test soldering better than soldering") and see how they
solder and then do an extended burn in to make sure they are okay.
Unfortuantley, the typical response I get is "The boards were expensive
and I need to use them to meet production orders." Fortunately, there has
never been solder assembly issues or reliability issues with these stained
board. Our telecommunication customers are extremely concerned about
product reliability because they deploy out product on towers in vastly
different environmental conditions and the last thing they want are
failures where someone has to go out and climb a tower and replace
products. Because of their reliability concern we keep very good records
of product serial numbers and issues experienced in manufacturing so if
the use of stained boards were causing a reliability issue we could would
know. As I said previously we've never experienced any reliability issue
associated with the use of immersion silver surface finish.
I've copied Steve on this email in hopes that he can post the attachment
on his web site so other TNers can see the 15 and 7 1/2 year old immersion
silver boards.
Subject: Re: IPC-4553
From: David D. Hillman
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
[log in to unmask]
Date: Wed, 9 Feb 2011 10:17:31 -0600
Content-Type: text/plain
Hi Richard - very good discussion! I have the luxury of having a SERA
tester to measure the oxidation state of my immersion silver pwbs so I can
determine just have bad things are getting. Here is some wording we use on
our product floor to assist with the "changing visual appearance" of
immersion silver finishes. This rule of thumb isn't perfect but has been
helpful.
Immersion Silver Visual Appearance Rule of Thumb:
Immersion silver surface finishes will discolor as a printed wiring board
goes thru the assembly process. This discoloration is oxidation and not
corrosion with one exception. The typical discoloration has a yellow to
goldish tan to light brown visual appearance which is cosmetic in nature.
If the pwas have a dark brown to black visual appearance then they have
been either mishandled, were left damp going into their ESD bags or the
plating is bad. So rules of the road:
1) If the pwas have a yellow to goldish tan visual appearance in an area
that is not going to be soldered, no action required.
2) If the pwas have a yellow to goldish tan visual appearance in an area
that is going to be soldered, no action required unless we encounter
soldering issues.
3) If the pwas have a light brown visual appearance in any areas of the
pwa, then we should review our handling procedures to make sure we are not
putting pwas in bags damp or not handling the pwas by the edges. We should
also inspect the bare pwbs in stock to see if they have a light brown
appearance prior to assembly.
4) If the pwas have a dark brown to black visual appearance in any areas
of the pwa, then we have a problem and need to find root cause.
As you detailed, rubber bands and tape cause major issues for immersion
silver pwbs turning black due to sulfur and chloride contamination
Dave Hillman
Rockwell Collins
[log in to unmask]
"Stadem, Richard D." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/09/2011 08:49 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Stadem, Richard D." <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] IPC-4553
In terms of losing solderability on the secondary side after a single trip
through the reflow, I think you have immersion silver finish confused with
immersion tin. Immersion silver does not usually degrade significantly
after a single reflow excursion.
But again, it depends (ka-ching).
There are many immersion silver plating products, some not as good as
others, and there is a huge variation amongst the plating companies that
apply these products. Like any other plating, it depends on which product
you use, and which plating company or PWB fabricator you use. Some IAg
products have a much superior co-inhibitor that prevents tarnishing and
oxidation.
Minor tarnishing (yellowing) of immersion silver has very little effect on
the DPMO of a given PWB. Black areas caused by direct contact with
sulfur-bearing desiccant packages, rubber bands, tape, paper (including
the Moisture Indicator cards) are a completely different story; these will
have significant impact on solderability, and the flux has little or no
effect on this.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Wednesday, February 09, 2011 8:33 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-4553
Good point. Solderability depends heavily on your flux I would say. Those
using a high activity, halide containing formulation would have an easier
time than those with ROL0. Plus, the additional predicament is that the
oxidation may be minor when the PCBs are received, and they solder just
fine, but after 6 months or so in stock it is worse, or even after 1 trip
down the reflow oven making Side 2 unsolderable.
-----Original Message-----
From: Jack Olson [mailto:[log in to unmask]]
Sent: Wednesday, February 09, 2011 9:11 AM
To: [log in to unmask]; Glidden, Kevin
Cc: Jack Olson
Subject: Re: IPC-4553
Good question.... and when looking at an actual board, how is one to
determine
visually if we are looking at "staining" or "oxidation/corrosion"?
Inquiring minds
want to know.
(many would say that even oxidized boards are solderable and acceptable.
right? I think I just read that somewhere...)
Jack
.
On Tue, 8 Feb 2011 09:20:44 -0500, Glidden, Kevin
<[log in to unmask]> wrote:
>Morning everyone,
>I have a question on IPC-4553, specifically, section 3.1 "Visual", and
specifically regarding staining of immersion silver. The text states "The
coverage shall be complete and the finish shall be uniform on the surface
to be
plated (see Figures 3-1 through 3-5 for properties visually identified
with IAg
plated surfaces)" Figure 3-1 shows 'Example of Uniform Plating", with no
staining. Figures 3-2 through 3-5 show staining. Is this to imply
(without text
to support) that any staining of immersion silver is determined to be non-
uniform and therefore a defect?
>Thanks.
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 Glidden, Kevin
Sent: Tuesday, February 08, 2011 9:21 AM
To: [log in to unmask]
Subject: [TN] IPC-4553
Morning everyone,
I have a question on IPC-4553, specifically, section 3.1 "Visual", and
specifically regarding staining of immersion silver. The text states "The
coverage shall be complete and the finish shall be uniform on the surface
to be plated (see Figures 3-1 through 3-5 for properties visually
identified with IAg plated surfaces)" Figure 3-1 shows 'Example of
Uniform Plating", with no staining. Figures 3-2 through 3-5 show
staining. Is this to imply (without text to support) that any staining of
immersion silver is determined to be non-uniform and therefore a defect?
Thanks.
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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.aspx?Pageid=E-mail-Forums for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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.aspx?Pageid=E-mail-Forums for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
-----------------------------------------------------
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
