TECHNET Archives

July 2008

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:
Dale Ritzen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Dale Ritzen <[log in to unmask]>
Date:
Mon, 7 Jul 2008 07:21:00 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (116 lines)
Rex et al,
We have had the same problem with white immersion tin finishes. They are to
be avoided if you can talk your customer into something else. We are
currently in the process of talking with our white tin customer about an
ENIG PCB finish.

However, if you MUST use them, there are some reflow profiling changes that
you can use to successfully do this most of the time (and they will make
your process guys go bonkers). They mostly concern running at the lowest end
of your Pb-free reflow temperatures (read: so you get MOST of the solder
paste "BB's" to flow) and praying that the copper-tin mix on the exposed
side doesn't start changing chemically before you reflow it. We have found
that minimizing the heated, non-soldered surface exposure to oxygen does
help a lot (i.e. nitrogen atmosphere during 1st and 2nd reflow). Plus, we
store the boards that have completed the SMT process in a nitrogen cabinet
between the SMT and PTH steps of the build. This does slow down the
oxidizing effect on the surface of the tin, but it is not the final answer
since it does nothing to stop the creation of Tin/Copper intermetallic under
heat. Yes, all this extra handling/process control raises the price of the
completed assembly significantly.

The most effective process is to use brand new boards (no shelf life), speed
the product through any/all processes it needs to go through at the lowest
temperatures possible (that is tough with Pb-free solders), and minimize
exposure to oxygen until the product is finished goods. Actually, the final
solution is to avoid immersion tin like the Black Plague...

Dale Ritzen, CQA
Quality Manager/ISO Management Representative
Austin Manufacturing Services
  

-----Original Message-----
From: Rex Waygood [mailto:[log in to unmask]]
Sent: Friday, July 04, 2008 4:35 AM
To: [log in to unmask]
Subject: [TN] Immersion Tin Problem

We do not usually use Immersion Tin finish boards but we have some with a
problem.
The boards are about 10-12 weeks old, stored in original packing, double
sided PTH and lead free processed.
Side 1 processed OK
Side 2 had some non-wet problems (Profiles and dwells etc are industry
'norm')
Hand soldering has proved to be nigh on impossible.
The immersion tin is within the thickness specified (typical values 1.1 to
1.2 micron)

Should we have avoided ImSn (as we have done previously)?

Is the spec for the ImSn OK?

Has the PCB mfr done something wrong?

Have we? (apart from accepting ImSn)

Rex


Rex Waygood
Technical Manager
 
PartnerTech Poole Ltd
Benson Road
Poole
Dorset BH17 0RY
United Kingdom
 
Tel: +44 (0)1202 674333
Fax: +44 (0)1202 678028
DDI: +44 (0)1202 338222
Mob: +44 (0)7887 997403
 
[log in to unmask]
www.PartnerTech.co.uk


----------------------------------------------------------------------------
---

The information contained within this e-mail and any attachments contained
therein may be confidential and/or legally privileged and is for the use of
the intended recipient only. If you are not the intended recipient please
delete it from your system and notify the sender by return e-mail. The
content of this e-mail may not be copied or disclosed to any third parties
without prior permission from the sender.

 

E-mail is susceptible to data corruption, interception, tampering and
viruses. We do not accept any liability for any such incidents or any
consequences thereof.
---------------------------------------------------
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