This is really hard to say. We do not operate a lead free environment, in fact we are very much the other way. So, we tin anything and everything that is marked Rohs compliant, or gold. We do much work for NASA manufacturers and we must have a lead/tin coating on all component leads. So, because the commercial world is trying to force us to buy Rohs components, even when we don't want them, we pre tin everything. Because this problem has been going on for a couple of years, off and on. It is possible that this began with the Rohs thing, but I don't really know that for sure.
Jack
-----Original Message-----
From: Ian Hanna [mailto:[log in to unmask]]
Sent: Wednesday, March 21, 2007 12:15 PM
To: TechNet E-Mail Forum; Jack Evans
Subject: RE: [TN] Whisker contamination is solder pot
Did you see this before you started tinning lead-free components?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Evans
Sent: Wednesday, March 21, 2007 2:04 PM
To: [log in to unmask]
Subject: Re: [TN] Whisker contamination is solder pot
Michael,
thanks for your reply and here are the answers, best I know:
1. What is the capacity of the solderpot?
This solder pot holds about 12 lbs.
2. What is the flux being used?
Almost exclusive to Kester 186-25, but a few drops of a kester OA might be used in extreme circumstances. The exceptional use of OA is so infrequent that I would rule it out all together, being used maybe once or twice every six months.
3. What is the material the pot is made of?
I am almost completely sure that this is milled out of stainless, but the photo copied manual that I have for this doesn't specify. It does not appear to be magnetic.
4. Does the problem show up on a new pot charge or does it require time to develop if so how long?
I have this problem today and it has been two weeks since I changed the solder. We had a HUGE batch (for us) of parts go through this this week,
about six hundred soic's. These particular components were lead free and we were having a difficult time getting them to reflow in the smt process without pre tinning them.
5. What is your definition of "polarized metal stuff"? Are you saying magnetic or are we getting into dipole moments and ligand field theory?
Well, often when we see this fine hairlike strand, we have to heat the lead and scrape it off with an iron. It doesn't become molten in normal soldering
temperatures and it doesn't want to let go of the lead that it is attached to. If we use braid, we often find ourselves chasing it up and down the lead.
Sometimes it seems to attracted to the soldering iron tip, as if magnetic and somtimes not. We use metcal tips.
I changed this solder pot today and used a new lot/date code of solder.
So, I
expect that this problem will appear to go away and I will assume that I have solved the problem. Then, sometime in the future, I will rear it's ugly head
again. We had this problem in our Corfin tinning system and we blamed
the
solder for several months. Finally, they removed the solder pot and replaced it with a brand new lot of solder and the problem went away. The lot date codes of solder that I am using have nothing to do with that story, but I wonder if in the past, this pot could have been contaminated and there are gremlins floating around in there that only show up on occasion???
Jack Evans,
Aeroflex Colorado
---------------------------------------------------
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
-----------------------------------------------------
|
