Steve:

I was in the same ballpark except that my part is somewhat smaller.

I can give you more details if you call me, if needed..

A quick summary of events ........

We're using an Actel CQ-132, 132 lead, 25mil pitch.
Using this here 'Net I got a great lead for a suggested land pattern from
Bob Vanech over at Northrup.
Got our design folks to agree to the suggested land pattern.
Sent land pattern to Fancort, who made me a die for forming this part in a
pneumatic press (12K)
(Die 9K, press 3K)
The part is programmed with the tie bars on.
When we get the part on the floor, we have to remove the corner metal
section that joins the tie bars.
Part is formed in the Fancort press and then transferred to a special matrix
tray that holds the part body without any pressure on the leads.
We then use a standard solder pot, and with a little practice and steady
operator hands (not mine !)
We lightly (I mean lightly) brush RMA flux on the feet along one side of the
QFP while holding the part with a high quality vacuum pencil.
We then dip the leads into the solder pot. The dip barely touches the top of
the molten solder with a quick withdrawl.
With a little practice, no bridges, comes out quite nice. Remember, only try
to tin the "feet"
Lots of articles in past periodicals and there is a "how to"document from
EMPF called "manual tinning of fine-pitch"
By the way, we have also done an analysis that shows that by leaving the
gold on the part will not affect the solder joint due to the
insignificant amount of gold remaining on the "feet" of the QFP. (Foot size
~ 50 mils by 12 mils wide.)
But we're going to tin the parts anyway our whole program will use about 50
parts over a years time.
I was lucky. I have only one part to deal with .

Bill Kasprzak
Moog Inc.
716-652-2000 ext 2507
 ----------
From: Stephen R. Gregory
To: [log in to unmask]
Subject: [TN] Pre-Tinning Fine Pitch...
Date: Tuesday, September 28, 1999 7:34PM

Hi ya'll!

Boy, I may have quite a task ahead of me. There's this assembly that has hit
the floor that has just about every part (CQFP's and ceramic SOIC's) in the
un-formed state, and we've got to form and trim, then Pre-tin the gold
plated
stuff. I've already got a call into Six Sigma to get a quote on doing this
stuff for me, but it may turn-out that we won't have the time to deal with
this build and sub-contracting the forming and trimming, and pre-tinning out
(what's new?).

But in case I have to pre-tin the CQFP's myself, are there any tips that
anyone can share to help me get through this as painlessly as possible?
These
parts are 320-pin 25-mil pitch and still have the tie-bars attached. I've
got
a bottle of nitrogen and plan to "Rube-Goldberg" me an enclosure to blanket
the pot with nitrogen over the tinning pot that I'll be using...I think
that'll help to cut down on the bridging I'll see. I'm going to use an RMA
flux as well...any other suggestions? PLEASE?

Thanks!

 -Steve Gregory-

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