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'[EE] Quick Easy Desoldering of DIP packages (salva'
2010\07\20@200316 by Forrest W Christian

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I asked a few months ago about how to desolder dip packages, and got a
wide range of answers - at this point I've tried several and either I'm
missing something or none of them work well.

To be clear, this is for re-work of a circuit board - usually either a
inserted-backwards or incorrect part on the board which needs to be
removed and replaced.  To date, the best way we've found is to clip all
the leads and then clean up each hole individually, which is a serious pain.

Other things we've tried:

Hot air to heat the component - top side, package seems to self-destruct
before the leads get hot enough to melt the solder.  Bottom - hard to do
without scorching board.  Plus, there seems to often be collateral
damage to nearby parts (aka capacitors) with the hot air reflow (when
done on the top).

Various methods to heat pins simulataneously - either top or bottom.  
I've tried irons with long metal pieces, or a solder gun with a custom
copper wire 'tip', etc.   Don't seem to be able to get things hot enough
for long enoguh to make this work.

Solder sucker and/or desoldering iron (vacuum) on each individual pin:  
Hard to get all of the pins cleaned out enough to pull the chip out,
although sometimes we do this first and then clip any remainng attched
leads to help ease the cleanup.

I haven't tried any miniature solder pots/waves yet...

So, is there a mechanism others have found that will allow one to
quickly and easily remove a soldered-in dip package, preserving the
board, not necessarily the DIP?

-forrest

2010\07\20@201811 by David Duffy (AVD)

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Have you tried the very low melting point solders?

You add in some flux and the special solder and the row of joints stay
molten for much longer.
David...

On 21/07/2010 10:03 AM, Forrest W Christian wrote:
> I asked a few months ago about how to desolder dip packages, and got a
> wide range of answers - at this point I've tried several and either I'm
> missing something or none of them work well.
>
>    
--

___________________________________________
David Duffy        Audio Visual Devices P/L
Unit 8, 10 Hook St, Capalaba 4157 Australia
Ph: +61 7 38235717      Fax: +61 7 38234717
Our Web Site: http://www.audiovisualdevices.com.au
___________________________________________

2010\07\20@213344 by Xiaofan Chen

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On Wed, Jul 21, 2010 at 8:03 AM, Forrest W Christian <spam_OUTforrestcTakeThisOuTspamimach.com> wrote:
> I asked a few months ago about how to desolder dip packages, and got a
> wide range of answers - at this point I've tried several and either I'm
> missing something or none of them work well.
>
> To be clear, this is for re-work of a circuit board - usually either a
> inserted-backwards or incorrect part on the board which needs to be
> removed and replaced.  To date, the best way we've found is to clip all
> the leads and then clean up each hole individually, which is a serious pain.

If you can sacrifice the chip, that is still one of the easiest solution.
I have never really worked with DIP packages except a brief one
month work long time ago. At that time, ICs were considered
expensive and we had the requirement of not destroying the IC.
The main tools used were cheap soldering iron, different types of
medical syringe and desoldering pump (solder sucker). The
syringe seemed to be effective for the DIP packages. I was not
good at it but there were quite some engineers/workers who
had no issue to remove those DIPs. At the time, I did not know
there were good stuffs like hot-air rework station or even solder
wick.

I am still not so good at soldering after so many years (ok at
0603/SOIC, so-so at 0402/SSOP, not okay with QFN and other
fine pitch components) since the technicians here are in general
much better than I. And in the rare case the technicians could
not do it, we have the production floor girls who can do almost
any possible rework.

--
Xiaofan

2010\07\20@230208 by Charles Craft

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www.chipquikinc.com/

On 7/20/2010 8:18 PM, David Duffy (AVD) wrote:
> Have you tried the very low melting point solders?
>
> You add in some flux and the special solder and the row of joints stay
> molten for much longer.
> David...
>
> On 21/07/2010 10:03 AM, Forrest W Christian wrote:
>    
>> I asked a few months ago about how to desolder dip packages, and got a
>> wide range of answers - at this point I've tried several and either I'm
>> missing something or none of them work well.
>>
>>
>>      

2010\07\20@233517 by Sean Breheny

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I can second this recommendation. It works amazingly well. The solder
has a rather exotic composition (Indium-Lead-Tin or for Pb Free,
Indium-Bismuth-Tin I think) and is very expensive (about $10 per foot)
as a result but it will stay molten for about 10 seconds after
removing the iron. It also requires the use of special flux and you
have to clean the board well afterwards to prevent residue of this
special solder from alloying with any new solder you apply since that
may result in a poor joint.

So, I think it is the best solution for doing this perhaps once or
twice per week. If you need it much more often, then it might be
cheaper in the long run to buy a specialized desoldering station.

To do this without Chip-Quik:
I would suspect that your soldering iron may not be getting hot
enough. If you have a good iron and a really wide tip which can hit
all the pins on one side of the IC at once, you should be able to
alternate between the two sides and gently "work" the chip out fairly
well. What kind of iron do you have?

Sean


On Tue, Jul 20, 2010 at 11:01 PM, Charles Craft <.....chuckseaKILLspamspam@spam@mindspring.com> wrote:
{Quote hidden}

> -

2010\07\20@233737 by Robert Young

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> Date: Tue, 20 Jul 2010 18:03:43 -0600
> From: forrestcspamKILLspamimach.com
> To: .....piclistKILLspamspam.....mit.edu
> Subject: [EE] Quick Easy Desoldering of DIP packages (salvage board, not the        DIP)
>
> I asked a few months ago about how to desolder dip packages, and got a
> wide range of answers - at this point I've tried several and either I'm
> missing something or none of them work well.
>
> To be clear, this is for re-work of a circuit board - usually either a
> inserted-backwards or incorrect part on the board which needs to be
> removed and replaced.  To date, the best way we've found is to clip all
> the leads and then clean up each hole individually, which is a serious pain.

Least damage way to board I've found is to clip the pins as you say.  Then with the iron and some tweezers, pull out the rest of the pin from each hole.  I wipe a flux pen down the row first.  Then use a powered solder sucker (either a PACE or I've got a no-name clone on another bench).  If you size the tip right and keep the filters clean it goes quick and seldom loose a pad or barrel.

If I need to salvage the chip whole for any reason, I use the powered solder sucker and size the tip to just fit over the tip of the lead.  Again wet the joints with a flux pen.  As the solder melts I give the lead a little jiggle and trigger the vacuum.  This seems to help remove all the solder between the pin and the wall of a plated hole.  Much higher success rate popping out the chip with little or no damage to the board.

When I used to use a Sold-a-Pullt (the blue ones) the best trick I found was to reshape the tips a little bit.  Notch them slightly so that you can get a "seal" around the pin and pad while leaving the iron in place.  Also keeping the tube clean and the O-ring lubricated kept the gizmo producing a good vacuum.  And as always, a little fresh flux to help the solder flow.

Rob

                                           

2010\07\20@234755 by Forrest W Christian

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Yeah, I have used chipquik regularly with surface mount..   I had played
a bit with the through hole and found it to be helpful, but the alloy is
so expensive that it doesn't 'feel' like the right solution.

-forrest

On 7/20/2010 9:01 PM, Charles Craft wrote:
{Quote hidden}

2010\07\21@044838 by Mike Harrison

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>Solder sucker and/or desoldering iron (vacuum) on each individual pin:  
>Hard to get all of the pins cleaned out enough to pull the chip out,
>although sometimes we do this first and then clip any remainng attched
>leads to help ease the cleanup.

One trick for quick removal - IC pins are often magnetic, so clipping pins, then holding a  magnet
above while melting the solder makes them jump out as soon as the solder melts.

Large tips which contact all pins at once can work well if the pins aren't splayed and the iron is
powerful enough, but you generally need to preload some solder onto the tip to get good thermal
contact.
As with any soldering process, you can never have too much flux. Brushing a flux pen over the joints
first can work wonders.

Probably the best tool is a good heated continuous-vacuum desolder iron , ideally Metcal. For really
troublesome pins soldered to internal multilayer groundplanes, heating with another iron on the
component side helps.
The trick is to not be too quick on the vacuum - don't suck til the solder has been molten for a
second or so - this allows heat to transfer all the way through the hole - premature sucking tends
to leave some un-molten solder. As mentioned before, wiggle the pin while sucking to clear all
sides.

Also remember that thermal contact and surface tension is everything - if a pin isn't quite freed by
the first desolder attempt, it's generally quicker to resolder it and repeat than try getting the
last bit of solder out.


2010\07\22@042109 by Peter

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I have posted on Usenet seeking collective wisdom on 'universal' ROHS solder
which is insenstitivy to alloying with other solders such that the weld is
reasonably good and close to eutectic behavior. The answers I got were no
encouraging. The 'hard old' (and tedious and bad for boards) method is the one
which works best, i.e. completely cleaning off the residue off the board and
iron tip (!) several times if necessary, and then using the new alloy to solder.

I heard SN100C is very good for all-around use and low cost, and somewhat well
behaved when mixed with SnPb residues, and some audiophool threads claim that
quad eutectic solder might be 'very good'. I do not know enough metallurgy
physics to judge if bringing in a complex 'outlandish' alloy to the existing one
will somewhat mitigate the effect of the existing alloy on the result alloy.

This is relevant to the thread because of what happens when the alloy formed by
by the new and old ROHS solders is *not* eutectic. The behavior ranges from that
of immiscible alloys swirling together without alloying, to something that stays
liquid for a surprising amount of time after removing heat.

It is this latter behavior which is what I was trying to avoid, and *may* be
interesting for board-friendly chip removal. In short, one could deliberately
add an 'incompatible' (metallurgically, for soldering purposes) ROHS solder to
the joints being processed and then rely on the bad characteristics of the alloy
to remove the part easier. And it does not have to be Indium based ($$$
expensive). Most ROHS solders are not compatible with each other and with SnPb
so just picking two and trying might work.

Also some people use a solder bath to mass remove parts from old boards (in SE
Asia). This is the same solder bath used to make the boards usually. The problem
is that parts stuffed for wave soldering have bent pins which prevent them from
falling out in the bath. The SE Asia method to deal with this is a knife edge
that  rips the parts out. You probably want something more delicate, such as
tying a steel wire under the chip to remove and then use the bath and pull
(gently) on the wire loop. Heat resistant chip inserters/extractors can also be
used. The board is ALWAYS heated from the bottom, whether with a bath, a hot
plate or with hot air.

My favorite method to remove stubborn parts is to preheat the board with a 150C
hot plate. After that, I use normal solder wick and/or suction. The 150C heating
corresponds to the factory preheating used before the solder bath for pre-fluxed
boards (most of them) and is safe in most cases even if prolonged considerably
to achieve heat soaking. Solder flow with preheating is much better than
without, with the same power iron (usually 50W thermostated). By stubborn parts
I mean large non-removable heatsink parts, and certain flyback and SMPSU
transformers and inductors mounted with hollow rivet solder points to reinforce
the board.

Setting the iron temperature is more critical for desoldering than for
soldering, and a high power thermostated iron with a large sharp edged chisel
tip works best. The sharp tip is used to lift the 'bent down' pins of certain
through hole parts. To avoid damage to the pad it is necessary that this lifting
be done such that the other contact point of the 'fulcrum' is off the pad, on a
copper-less part of the board if necessary. The wide chisel chip usually permits
this. It also brings a lot of heat to the part where needed.

Most desoldering braids do not carry enough flux for sustained desoldering work.
I always add pure rosin (solid) to them either as powder or by pulling the braid
through a rosin block with heat from the iron.

These technologies are now decades old, I worked for 14+ years almost
exclusively with SMD after that. That does not make them less good however ;)

-- Peter


2010\07\23@073747 by cdb

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:: Solder sucker and/or desoldering iron (vacuum) on each individual
:: pin:
:: Hard to get all of the pins cleaned out enough to pull the chip
:: out,

I don't recall how many layers your board has or if it has large power
planes, but gel flux (expensive'ish) dotted around the pins to be
desoldered, and then a desoldering iron applied with 1mm or less tip size,
allow solder to heat through hole etc, wiggle tip head around, the pin
should move, then suck.

Before buying gel flux, often applying new solder to the pin will 'reflux'
the joint plus act as a interface (can't think of the proper word at the
moment) to the desoldering tool.  Solderbarid can also be more effective
sometimes I've found than a desoldering iron.

Motto: To desolder, solder is needed!

Colin
--
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2010\07\23@085314 by Carl Denk

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Has anyone used ordinary (plumbing for copper pipe joints) flux. It is
inexpensive, not acid variety, comes as a paste, almost a gel. Would
this be acceptable from a chemical action viewpoint? My favorite is
Oatey #5 soldering paste. hazardous ingredients are  zinc chloride and
ammonium chloride. I guess the chlorine might be an issue.

On 7/23/2010 7:37 AM, cdb wrote:
{Quote hidden}

2010\07\23@171621 by John Coppens

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On Tue, 20 Jul 2010 18:03:43 -0600
Forrest W Christian <@spam@forrestcKILLspamspamimach.com> wrote:

> Hot air to heat the component - top side, package seems to
> self-destruct before the leads get hot enough to melt the solder.
> Bottom - hard to do without scorching board.
I believe most of the damage described is due to lack of patience. I've
desoldered lots of packages without any problem, but the secret is to
give the DIP package (and the board) time to heat up. Not to crank up
temperature.

It takes quite a bit of time for the necessary heat to build up so solder
melts... 20 - 30 seconds or more.

Joh

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