how to remove lqfp package

[Jeff]

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering iron.
I think that method stresses the pads on the board when they cut. I believe
they cut many leads at once. Any comments?

Thanks,

Jeff

 

[Rene Tschaggelar]

Jeff wrote:

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering iron.
I think that method stresses the pads on the board when they cut. I believe
they cut many leads at once. Any comments?

I have a tool from a dentist with a fine tip that lets me
lift a single pin of a 0.8mm to 0.5mm pin distance case.
I wouldn't heat the whole board with hot air as some other
components may overheat or be blown away.
Clipping might lift the pads and damage the copper.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

 

[John Larkin]

On Sun, 15 May 2005 16:13:51 GMT, "Jeff" <koebrich@sbcglobal.net>
wrote:

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering iron.
I think that method stresses the pads on the board when they cut. I believe
they cut many leads at once. Any comments?

If the pads aren't being ripped off the board, they're not being
overstressed.

John

 

[Leon Heller]

"Jeff" <koebrich@sbcglobal.net> wrote in message
news:3zKhe.101$VS6.63@newssvr19.news.prodigy.com...

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering
iron. I think that method stresses the pads on the board when they cut. I
believe they cut many leads at once. Any comments?

This is one of those areas where everyone has their own favourite technique.
ChipQuik is another technique that I often use:

http://www.chipquik.com/

Leon

 

[Ken Smith]

In article <3zKhe.101$VS6.63@newssvr19.news.prodigy.com>,
Jeff <koebrich@sbcglobal.net> wrote:

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering iron.
I think that method stresses the pads on the board when they cut. I believe
they cut many leads at once. Any comments?

Cutting the leads with very sharp cutters may work ok but the clean up
with a soldering iron may be slightly toasting the PCB.

There is a material sold for removing such things with no damage at all.
It looks like solder but has a vert low melting point. You just use your
normal preheater and put this stuff on the joints. It melts and disolves
the solder freeing the IC without even the slightest damage to the PCB.

--
--
kensmith@rahul.net forging knowledge

 

[John Miles]

In article <d686gu$l45$1@blue.rahul.net>, kensmith@green.rahul.net
says...

There is a material sold for removing such things with no damage at all.
It looks like solder but has a vert low melting point. You just use your
normal preheater and put this stuff on the joints. It melts and disolves
the solder freeing the IC without even the slightest damage to the PCB.

That's pretty wild. How does it 'dissolve' solder? Got a link?

I use a Dremel tool with a cutting wheel to remove flat-pack ICs, then
follow up with solder-wick to remove the severed pins from the pads
without stressing the board too much. Seems to work pretty well. (Also
very effective for removing old-fashioned DIPs.)

-- jm

------------------------------------------------------
http://www.qsl.net/ke5fx
Note: My E-mail address has been altered to avoid spam
------------------------------------------------------

 

[Boris Mohar]

On Sun, 15 May 2005 16:13:51 GMT, "Jeff" <koebrich@sbcglobal.net> wrote:

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering iron.
I think that method stresses the pads on the board when they cut. I believe
they cut many leads at once. Any comments?

Thanks,

Jeff

First apply a lot of flux to the pads and wick up as much solder as possible
using a solder wick. Thread a length of fine steel or similar wire under
the chip and behind the row pads. Tie one end of the wire to the board.
Pull the other end tight at 45° angel to the pads. Apply soldering iron to
the first pad where the wire is pressing behind the pad. The little
remaining solder will melt and the wire will slip behind the next pad in
line. With little practice you can unzip a chip and preserve both the chip
and pads.



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

 

[Richard H.]

John Miles wrote:

That's pretty wild. How does it 'dissolve' solder? Got a link?

We use this system, which is basically the same as ChipQuik:
http://www.zeph.com/lowmelt.htm
At $75 it's pricy, but 16 feet is enough to desolder ~75 QFP-128 chips,
salvaging just one board makes it payoff.

Using just a pre-heater at 150 C, this stuff mixes with the solder and
lowers its melting point so it's liquid. The chip lifts off without
even needing an iron.

This keeps the board and other components below recommended temps, and
nearby components stay firmly soldered. It's actually gentle enough
that the chips could be re-used, if only there was a way to clean off
their leads.

Cheers,
Richard

 

[Ken Smith]

In article <W1Phe.20752$Fa1.10625@fed1read02>, Richard H. <rh86@no.spam> wrote:

John Miles wrote:
That's pretty wild. How does it 'dissolve' solder? Got a link?
[...]
This keeps the board and other components below recommended temps, and
nearby components stay firmly soldered. It's actually gentle enough
that the chips could be re-used, if only there was a way to clean off
their leads.

You can wipe the leads of a PLCC with paper to clean them. On a TQFP, it
would be very tricky to do without bending them.

--
--
kensmith@rahul.net forging knowledge

 

[Clifford Heath]

Richard H. wrote:

That's pretty wild. How does it 'dissolve' solder? Got a link?

I guess this must be bismuth. There's a eutectic alloy of tin,
lead and bismuth in which the tin/lead ratio is nearly 60/40,
which melts at around 94C - below the BP of water. Sounds like
this solder is s.t like this, perhaps with more bismuth. Time
for some US EE who's a shooter to try it with some bismuth shot,
now sold as a replacement for lead shot?

 

[Rich Grise]

On Sun, 15 May 2005 16:13:51 +0000, Jeff wrote:

I am having an argument (a friendly one) with co-workers about removing
small 32, 48, and 100 lead LQFP packages from production circuit boards. I
think they should use the hot air rework equipment we own, but they like to
clip them off with cutters and then clean up the pads with a soldering iron.
I think that method stresses the pads on the board when they cut. I believe
they cut many leads at once. Any comments?

Time them. Clipping, then unsoldering pins, sounds very time-consuming,
not to mention messy.

So I vote hot-air.

I've done DIPs with a solder sucker and wick, but it's also time-consuming,
and I wouldn't want to try it on a package with leads on all 4 sides.
Although, you could use some pointy thing - stick it between the package
and the jog in the lead, and shove it in as you unsolder one lead at a
time and lift them.

In any case, the old solder will have to be removed somehow.

HTH!
Rich