QFP soldering

From: Richard Erlacher <edick_at_idcomm.com>
Date: Thu Jan 24 13:58:00 2002

What may be of help is to take a useless (broken) QFP of the same
size/shape/pin-pitch, and lay it on the board, which I presume has no solder
mask, and paint over the pins with clear nail polish. Once that's done, you
blow on the stuff until it no longer flows, then remove the QFP before the
nail polish dries. you then wait for the nail polish to dry. Once that's
done, you put the desired QFP in place and apply solder flux, then, with a
small, hot tip, solder the corner pins in place so the thing doesn't move
around, and then go back and solder the remaining pins, applying solder as
needed, but sparingly, and, after the whole thing's in place, put a solder
wick on top of each row of contacts, and wick up the excess solder. It's not
perfect, but it works pretty well and avoids those annoying solder bridges.

Try to keep the temperature pretty low, but high enough that the solder flows
readily. For that purpose, I'd use a narrow and fine-pointed tip that can
easily fit on a single pin. It's no trouble geting more than one pin, but
often it's necessary to hit just one, and that's what I'd try first.

Don't do ANYTHING to the leads on the QFP! They're already tinned. A little
liquid flux may help, if applied on top of the pins once theyre in place,
though. I'm going to have to buy stronger reading glasses before the next
time I do this.


----- Original Message -----
From: "Cini, Richard" <RCini_at_congressfinancial.com>
To: "'ClassCompList'" <classiccmp_at_classiccmp.org>
Sent: Thursday, January 24, 2002 11:50 AM
Subject: QFP soldering

> Hello, all:
> I am finally getting around to building the P112 Z180-based SBC from
> Dave Brooks (I got one of his last unpopulated boards). It has two 100-pin
> QFP chips (the Z180 and an SMC Super I/O chip), so, I bought the blade-like
> SMD soldering iron tip for my iron.
> So, here's the stupid question...how do I solder these things? Do I
> hold the iron parallel or perpendicular to the package leads? The board is
> pre-tinned, but I should I also tin the QFP leads?
> Any help appreciated.
> Rich
Received on Thu Jan 24 2002 - 13:58:00 GMT

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