Re: Favorite SMD chip removal method

Tim Wescott wrote:
> Entirely apropos to my question about Luminary JTAG access being screwed
> by software:
>
> What's your favorite way of removing large chips for board rework? I
> have about as low-tech a bench as can be used for SMD work -- an
> assembly microscope, a Weller WTCPN iron, and a will to not give up.
>
> Lately I've been using Chip Quick -- it's a low-temperature solder that
> dissolves regular solder and stays molten long enough that you can run
> your iron around the edge of the chip* and flip the chip off the board.
> Then you have to solder wick every bit of the stuff _off_ the board, go
> over it _again_ with regular solder to get the last bit off, solder wick
> _that_ off, and you're good to resolder. It's expensive, you need to
> take some care in cleaning up the board afterwards, it's time-consuming
> -- but it doesn't require any expensive equipment, and it seems to be
> quite gentle with the board.
>
> So -- what do you use?
>

I walk over to the kitchen, give my wife a kiss, steal some chocolate
out of the fridge when she isn't looking, then take a piece of thick
aluminum foil. This gets draped around the board and then I cut the chip
free, using an Exacto knife. Now I heat things with a Cooper heat gun. I
let a Rouladen-hook (like a kabob spike but 3x smaller) stick
underneath, at a very flat angle. This avoids me having to tug and risk
ripping pads off. When the hook starts to sag I know it's 2-3 more
seconds and I'll be able to just scoot the chip off onto the aluminum.

If in a rush I sometimes use a big old 150W iron. Melt some solder onto
the pins and slide that along. Then I take my thinnest valve adjuster
blade (don't need those anymore with modern cars) and slide it along
with it, goes between pins and pads (careful, never force it or a pad
will rip off).


> * Obviously this won't work for BGAs.
>

I never use any large BGAs. Too many reliability issues. A non-flexing
BGA on a flexing PCB is a bump failure waiting to happen.

--
Regards, Joerg

http://www.analogconsultants.com/

Tim Wescott wrote:
> On 07/06/2011 05:56 PM, Joerg wrote:
>> Tim Wescott wrote:
>>> Entirely apropos to my question about Luminary JTAG access being screwed
>>> by software:
>>>
>>> What's your favorite way of removing large chips for board rework? I
>>> have about as low-tech a bench as can be used for SMD work -- an
>>> assembly microscope, a Weller WTCPN iron, and a will to not give up.
>>>
>>> Lately I've been using Chip Quick -- it's a low-temperature solder that
>>> dissolves regular solder and stays molten long enough that you can run
>>> your iron around the edge of the chip* and flip the chip off the board.
>>> Then you have to solder wick every bit of the stuff _off_ the
>>> board, go
>>> over it _again_ with regular solder to get the last bit off, solder wick
>>> _that_ off, and you're good to resolder. It's expensive, you need to
>>> take some care in cleaning up the board afterwards, it's time-consuming
>>> -- but it doesn't require any expensive equipment, and it seems to be
>>> quite gentle with the board.
>>>
>>> So -- what do you use?
>>>
>>
>> I walk over to the kitchen, give my wife a kiss, steal some chocolate
>> out of the fridge when she isn't looking, then take a piece of thick
>> aluminum foil. This gets draped around the board and then I cut the chip
>> free, using an Exacto knife. Now I heat things with a Cooper heat gun. I
>> let a Rouladen-hook (like a kabob spike but 3x smaller) stick
>> underneath, at a very flat angle. This avoids me having to tug and risk
>> ripping pads off. When the hook starts to sag I know it's 2-3 more
>> seconds and I'll be able to just scoot the chip off onto the aluminum.
>
> OK, I'm slow -- by "cut the chip free" you mean you're cutting a hole in
> the aluminum foil, so you're only heating up the chip? When I first
> read that I thought you meant you were cutting off the chip at the legs,
> then cleaning up the legs later -- but that doesn't make sense with the
> rest of what you said.
>

Yes, just the foil, so that you get enough clearance around the pins yet
neighboring chips and SMT parts remain covered. Use thick foil, the good
stuff, not the thin stuff from the Dollar store :-)

--
Regards, Joerg

http://www.analogconsultants.com/