At 11:54 AM 2/25/02 -0500, Chris Loiacono wrote:
>I really despise PTH's in boards. However, I have some 40 pin PDIP PICS
>soldered into thru-hole proto boards that I need to remove. The boards are
>prototype quality with mask & silk, etc, but I notice that this particular
>vendor's copper tends to de-laminate very easily when re-working. I need
>these boards to survive without visible scars. Solder wick is out, likewise
>my inexpensive suction type tools since they tend to lift pads when enough
>heat is applied to get the solder out of the barrels.
>
>What is the safest and surest way to remove these chips? I will gladly buy
>another tool, as long as I won't need a new mortgage to pay for it...

I've used a variety of vacuum desoldering stations in the past and have 2
favorites: Weller DS-100 series and Metcal.  I have used the Pace, Hakko
and early OK Industries units but don't like them anywhere near as much as
I like the Weller.  The little hand-held Denon all-in-one units work great
for resistors or capacitors but are a little bulky, and therefore hard to
control when trying to ensure that every lead of a large DIP is free.

Are you close to anyone who has a decent desoldering station - and is
experienced in its use?  The tools are one thing - knowing just how the
lead feels when the solder is melted clean to the top of the board is
something else entirely.

If you want to purchase a tool - take a close look at the shop-air powered
Weller DS-100.  It is relatively inexpensive and the vacuum has a
respectable rise time.  The shop-air powered Metcal has a similar vacuum
rise time and is much better than the Weller when desoldering multi-layer
boards but costs at least triple the Weller unit.  Watch out for units that
have built-in electric vacuum pumps - the vacuum rise time is often too
slow and you do not get a nice clean hole.

One final note: once you have desoldered all the holes, grab hold of the
chip with some flat blade pliers - the little miniature 'duck bill' pliers
- just above the leads.  Wiggle the chip from side to side and rotate it
slightly.  You should see and feel all the pins move in their holes.  If a
pin is not free, re-solder the lead, then desolder it again.  You need to
have enough solder in the hole so that the desoldering tip has good thermal
contact with and makes a good seal against the pad.  A partially desoldered
lead is a real bear to free so don't try.  Fill the hole with fresh solder
and try again.

dwayne


Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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