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...
At first I thought "That's no sweat, these are 18C442's (ouch!) so they're
basically trash now anyway" but thinking further, the program burned will
support a different board quite well, so I would like to save the chips if
possible.
C
> "What is the safest and surest way to remove
> these chips?"
>
> We used to clip each IC pin with cutters - then remove
> each pin individually. This was on multilayer
> boards where we needed to replace a bad chip.
>
> Of course, the chip gets destroyed in the process ...
At 12:40 PM 2/25/02 -0500, you wrote:
>At first I thought "That's no sweat, these are 18C442's (ouch!) so they're
>basically trash now anyway" but thinking further, the program burned will
>support a different board quite well, so I would like to save the chips if
>possible.
Beg, borrow or otherwise get ahold of a desoldering station with a good
pump and controlled-temperature tip. It will make short work of this.
They cost maybe $1000 new. I've had bad experience with the cheaper
Weller ones.
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.
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> 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.
Try to avoid buying one of those electric plunger types. The price looks
attractive, but the performance isn't much to speak of. They also
produce smog in the form of desoldering fumes which are 'puffed' into
the air at each pump.
> 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.
>
I did one swap successfully today by putting a phase-angle controller on my
bulb-suction desoldering tool and finding the just-right heat setting. I
also turned a new tip shape in a l lathe, which also seemed to make a
difference. I got pretty good results by taking my time on each pin. It's
just not an ergonomically designed tool, and after an hour of multiple tries
on 40 pins, my hand had done enough for one afternoon.
> 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.
I never thought I would be doing much of this again, so I'll have to invest
in some new tools. The only thing close to a soldering station around my
town are probably branding irons for livestock.
>
> 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.
Exactly the kind of advice I can use. The last time I purchased a tool for
desoldering DIPS, I got what was then a new concept tool - a table-top
reflow station. That was in '77. Looking around, the whole idea seems to
have become obsolete.
> 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.
I made a small radiused shape on the tip, and I think it sealed better that
way - makes sense. If the suction actually gets to pull through the hole,
less solder should remain.
Is that what you mean?
> partially desoldered
> lead is a real bear to free so don't try. Fill the hole with
> fresh solder
> and try again.
This works with solder wick too, but how nice it is to get it on the first
try
those "try again's" are killer on pad adhesion!
I'm embarrassed to say that back in the 70's I ran a repair dep't for a
major commercial electronics house. - I had ten or fifteen people on any
given day troubleshooting boards and desoldering parts by the hundreds. Only
now am I learning how difficult their jobs were.
This, I fear is only a symptom of my real problem:
I need a better revision control system - and one that will fit all kinds of
micros with all done with all different compilers and languages. The
standard method of organizing MPASM files seems to leave a bit to be
desired.
This sounds like a new topic though. Maybe tomorrow.....
Thanks for the advice Dwayne. I start tool shopping tomorrow.
Do you have any thoughts on desoldering tools that also can function as a
hot-air reflow pen?
Sounds like it would be a useful feature for the SMT's?
>At first I thought "That's no sweat, these are 18C442's (ouch!) so they're
>basically trash now anyway" but thinking further, the program burned will
>support a different board quite well, so I would like to save the chips if
>possible.
Essentially it comes down to the fact that you save one or the other. It is
extremely difficult to save both when the tracks lift in the manner you
described previously.
If you really must save the chips, then the PCB will have to be a bit
sacrificial, and have a socket with patch wire repair. Easily done using
wire wrap wire as the repair wire. Done this many times before. With a PCB
properly washed down afterwards it can still look quite presentable.
If the PCB must be saved at all costs then the only way is to sacrifice the
chips. Cutting the legs, and then carefully removing the pins before sucking
the solder out of the holes is the only method.
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Hm. Maybe not. You can do it in a SMD reworking station by heating the
whole board and extracting the chips when the solder melts (you want the
top heat on low and the bottom way up high). You will probably need to
adjust the jigs to make the board fit etc. Of course I assume you have a
SMT reworking station ...
Peter
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A decision to do prototyping and short (very) run jobs in-house ia causing
me to get back into hardware after about 20 yrs. Hence, the need for advice.
I will likely have to buy or build everything needed, so I thought a tool
that could be used on PTH & SMT rework might be a good thing. {Quote hidden}
>
> > new mortgage
>
> Hm. Maybe not. You can do it in a SMD reworking station by heating the
> whole board and extracting the chips when the solder melts
> (you want the
> top heat on low and the bottom way up high). You will probably need to
> adjust the jigs to make the board fit etc. Of course I assume
> you have a
> SMT reworking station ...
>
> Peter
>
>
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If you do not need to save the pic then easiest way is to cut
Pic's pins from top then remove them one by one. If you need
To save the pic too you are going to need 2 soldering irons.
DO this
solder all pins together on both sides have some one
ready to pull the pic from the other side.
take both soldering irons and start heating both sides
at the same time and move your irons back an forward let
the person slowly pull it. I was able to remove 40 pins pics
without any damage. You need to do this fast
Ah, the 'little-by-little' method. I had to resort to this only once to
handle multiple pins that wouldn't cooperate.
Thanks for all the help.
I combined several of your tips and saved everything!
I found that a combination of a 'good tip seal' to get the bulk of the
solder out, the 'wiggled sucker' to get trapped solder from hidden behind
the pin areas, plus the 're-solder-and-try-again' method to make it all
work. I even used wick successfully on a couple of the more difficult pins.
Having precise control of my tip temperature was key. It's interesting to
note that I was removing these chips from SCR Phase-Angle boards. I used one
of these boards and a thermocouple to set my tip temp precisely. Combining
this with all the coaching, I am sure is why all the pads are still attached
to the boards.
This experience has me thinking of designing my own tool from
scratch...Hmmm.....
> Chris,
>
> If you do not need to save the pic then easiest way is to cut
> Pic's pins from top then remove them one by one. If you need
> To save the pic too you are going to need 2 soldering irons.
> DO this
>
> solder all pins together on both sides have some one
> ready to pull the pic from the other side.
> take both soldering irons and start heating both sides
> at the same time and move your irons back an forward let
> the person slowly pull it. I was able to remove 40 pins pics
> without any damage. You need to do this fast
>
>
> Andre Abelian
>
>
mitvma.mit.edu
