Ioan,
See my comments in the body of your memo.
regards,
Bev Christian
Carrier and Wireless Solutions
Nortel Networks
250 Sidney Street,
Belleville, Ontario
CANADA K8N 5B7
613-967-5407
-----Original Message-----
From: Tempea, Ioan [SMTP:[log in to unmask]]
Sent: Friday, January 28, 2000 4:25 PM
To: [log in to unmask]
Subject: [TN] Oxidation and solderability
Hi Technos,
I'm in the middle of a crossfire here. Everybody, that is our QA and
customer's QA are concerned about one rework method we are using.
Because one particular connector is very capilarity prone, if we touch the
leads using liquid flux, the flux ends up on the golden contacts, giving
interconnection problems. I decided that we should touch the connector
without using any flux, except for the one inside the solder wire.
The problem is that QA is concerned about the reliability of a joint made
without flux.
Ah, but you are not making joints without flux since you say above you are using cored wire. This should provide all the flux you need for the job.
Is the heat enough to break the oxide crust?
Only if there is enough solder to be mobile, enough solder that it can be moved around. Like moving the dross around on a solder pot with a spatula to expose the fresh solder. Even then you need to flux the part you are going to dip.
Will
intermetallics be there on both the pin and the pad?
You better hope that there is some intermetallic already on the pin and pad or you are not going to have a good joint. Now if your question is about the amount of intermetallic, this should only be a problem if you really crank up the heat on your soldering iron and leave it there for some time.
My question is: is there any experimental data available on the degree of
oxidation on HASL surfaces in terms of time?
Yes. I think you should be able to find that in the better text books on soldering. Also, Dr. Chris Hunt of the British National Physics Lab gives a solderability course where he presents this data. The short answer is that oxide formation is immediate. Sorry I have no hard data to share, as I am at home and my stuff is at work.
After how long an exposure to
ambient conditions the oxide layer is thick enough to require flux for
removal?
Tied into your question about crust. I would never try to solder without some flux present, unless you start talking about "fluxless" soldering methods where the parts are pre-treated in various gas/plasma mixtures, but that's a esoteric topic, don't worry about that now.
Our boards are touched within, at most, 48 hours after reflow. Is this
timing long enough to ruin the solderability of the pad and the component?
It should be months before there is a solderability degradation, assuming decent storage conditions.
Once again, some hard data is what I need, since I'm dealing with QA.
Thank you again for being there,
Ioan
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