Re: Stuffing boards with pulled QFP chips

[Chuck Guzis via cctech]

On 03/31/2017 06:15 PM, Jon Elson via cctech wrote:

> I have a project I do from time to time using 128-lead 14mm TQFPs
> with 0.4mm lead spacing. I use a stereo zoom microscope with a
> home-made LED ring light. First, I rub the pads with a pencil eraser
> to remove oxidation caused by reflow temps on the rest of the board.
> I put a tiny dab of solder on two pads at opposite corners. I then
> place the chip in place and reflow those pads.  If the alignment is
> not good enough, I can "walk" the chip a bit by reflowing one, then 
> the other pad.  Then, I apply liquid flux to the rows of leads with
> a wire dipped in the flux. And, then solder down the rows with a
> fine-tip soldering iron.  If a bridge develops, solder wick fixes
> it.

There are plenty of good Youtube videos describing this.  I use pretty
much the same method, but start off with just a binocular loupe and then
finish with a stereo microscope for final inspection.

The soldering  iron tip that works best for me is a rather broad chisel
tip.  I leave the fine tips for other work.

--Chuck

Re: Stuffing boards with pulled QFP chips

[Jon Elson via cctech]

On 03/31/2017 06:28 PM, allison via cctech wrote:


Is this something that an experienced hand can manually do?

Yes, definitely.  100 lead PQFP is perfectly doable if the lead pitch is not 
insanely small.  It takes a good fine tip soldering iron (mine is a Weller with 
a PTS tip), fine solder (preferably real, i.e., 63/37 non-PC solder).  Liquid 
flux is a big help, as is a magnifier and bright light or modest magnification 
microscope.

If you have to do a couple of dozen boards this gets very tedious, but for 
5-ish it isn't a big deal.


I have a project I do from time to time using 128-lead 14mm 
TQFPs with 0.4mm lead spacing.
I use a stereo zoom microscope with a home-made LED ring 
light. First, I rub the pads with a pencil eraser to remove 
oxidation caused by reflow temps on the rest of the board.  
I put a tiny dab of solder on two pads at opposite corners.
I then place the chip in place and reflow those pads.  If 
the alignment is not good enough, I can "walk" the chip a 
bit by reflowing one, then the other pad.  Then, I apply 
liquid flux to the rows of leads with a wire dipped in the flux.
And, then solder down the rows with a fine-tip soldering 
iron.  If a bridge develops, solder wick fixes it.


Jon

Re: Stuffing boards with pulled QFP chips

[allison via cctech]

On 03/31/2017 02:00 PM, Paul Koning wrote:
>> On Mar 31, 2017, at 1:51 PM, allison via cctech  
>> wrote:
>>
>> On 03/31/2017 06:32 AM, David Griffith via cctalk wrote:
 I'm down to the last few P112 boards for sale and am pondering
 another run of them because demand is steady.  One of the biggest
 challenges for the last run was getting the QFP-packaged 100-pin
 chips[1] in a state such that the pick-and-place robot wouldn't throw
 a fit about slight differences in lead position.  The stuffing house
 insisted that I send them new chips.  Pulls, though they looked
 perfectly okay to me, were not acceptable.  Does anyone here know
 anything about pick-and-place robots using pulled 100-pin QFPs,
 particularly a stuffing house that can work with such chips and not
 screw up?

 [1] The now-obsolete super-io chips


>> Is this something that an experienced hand can manually do?
> Yes, definitely.  100 lead PQFP is perfectly doable if the lead pitch is not 
> insanely small.  It takes a good fine tip soldering iron (mine is a Weller 
> with a PTS tip), fine solder (preferably real, i.e., 63/37 non-PC solder).  
> Liquid flux is a big help, as is a magnifier and bright light or modest 
> magnification microscope.
>
> If you have to do a couple of dozen boards this gets very tedious, but for 
> 5-ish it isn't a big deal.
>
>   paul
>
So happens I'm fully equipped on all counts.  Including the PTS tip. 
However my preference
for years has been the PTA7K (WTCP60) which is 1/4" wide!  Gets a few
pins done at a time... ;)

I've not gone over to the Rohs side, most of the solders are not fun to
work with though a
few have very active fluxes and solder aluminium well.   So its Kester
44 in 10 and
20 mil (inch mil) diameters.

I've done more than a few AD537 and similar Blackfin CPUs with their 288
BGA package that's
a challenge to pull and replace.

Allison

Re: Stuffing boards with pulled QFP chips

[allison via cctech]

On 03/31/2017 06:32 AM, David Griffith via cctalk wrote:
>>
>> I'm down to the last few P112 boards for sale and am pondering
>> another run of them because demand is steady.  One of the biggest
>> challenges for the last run was getting the QFP-packaged 100-pin
>> chips[1] in a state such that the pick-and-place robot wouldn't throw
>> a fit about slight differences in lead position.  The stuffing house
>> insisted that I send them new chips.  Pulls, though they looked
>> perfectly okay to me, were not acceptable.  Does anyone here know
>> anything about pick-and-place robots using pulled 100-pin QFPs,
>> particularly a stuffing house that can work with such chips and not
>> screw up?
>>
>> [1] The now-obsolete super-io chips
>>
>>
>
Is this something that an experienced hand can manually do?

Of all the CP/M platforms its one of the few I haven't done.  But
it keeps popping after I've long figured its long gone.

I'm not afraid of SMT as I proto using 0603 and 0402 parts
at uhf/microwave freehand.

Baving delt with layouts for BGA and large pinout devices usually getting
fiducial marks on the board so it can locate and position without
optical works.
One time the board designer messed up and we had to use existing fixed
points
for that.  PITA but it worked. After that I got into the board layout
bit and DFM.


Allison