R.I.P. for D.I.Y.

From: Peter C. Wallace <pcw_at_mesanet.com>
Date: Thu Apr 25 18:29:13 2002

On Thu, 25 Apr 2002, Tom Uban wrote:

> Peter,
>
> I've had this concern myself and have even made processor choices based
> on my fear of the hand prototyping of BGA parts.
>
> Would you please give us a synopsis of your experience and tips hand
> assembling BGA parts, including tools, temperatures, etc. ?



What I do for BGA protos is this:

1. Solder the BGA(s) first!
This is for a couple of reasons, its easier to inspect the soldering, and if
you mess up the BGA soldering you can start with a fresh board and not have to
remove the BGA part. (Though I have removed and resoldered BGAs with pretty
good luck)

2. Build a "frame" around the BGA by soldering pieces of scrap circuit board
material on all 4 sides of the BGA, leaving a little (5 mill) clearance on
each side. I do this with pieces of paper as a shim that I later remove. This
is the most critical part, the BGA part must be located in the right position
on the PC by the frame. The 5 mill clearanec on the side is so the BGA can
"float and settle" when the balls melt -surface tension will bring it into
perfect alignment with the PCB pads. I do the frame alignment by setting the
BGA on edge (vertical) against each of my frame pieces and checking the
ball/PCB pad alignment.

3. Put _A LOT_ of rosin core flux on the PC BGA pads. You dont need any solder
with the common solder ball type BGAs they have plenty in the balls.

4. Heat from behind with a heat gun. I use a standard $59 Granger heat gun.
This requires some pratice to avoid overheating the board. You can pratice by
soldering small SMT parts to scrap or used PCBs. Moving the heat gun around in
a small circular pattern will help avoid PCB damage. When the Rosin flux
really begins to smoke, the temperature is just about right. You can see when
the BGA solder balls melt, because the BGA chip will sink about 1/2 mm. When
you see it sink, Your done!

5. Checking: When the PCB is cool you need to remove the flux and inspect the
soldering. If the BGA is soldered properly the solder balls will have a
squashed appearance on all 4 sides of the BGA and you should be able see
through all the interball rows in both directions by along the underside of
the BGA. If the balls are not melted enough, you can re-apply flux and re-heat
The worst thing that can happen is that your frame is mis-aligned so far that
the balls ended up stikinf to 2 pads and have have merged underneath the BGA.
In that case you need to remove the BGA and try again (with a new part)


I have not been 100% successful but am close to 85% good solders first time...


>
> --tnx
> --tom
>
> At 12:46 PM 4/25/02 -0700, you wrote:
> >On Thu, 25 Apr 2002, Jos Dreesen wrote:
> >
> >> Allison wrote:
> >> >
> >> >almost impossible for the home builder ... and only the odd few (Tony?
> :-)
> >> >
> >> > Impossible? How?
> >> >
> >> Open any GSM phone and look at the components....
> >> There is NO WAY a hobbyist (not even Tony ( sorry chap !)) will be able to
> >> handle 200-300 pin BGA packages, with 0.8 or even 0.5mm pitch.
> >
> >Nonsense! I do 388 pin BGAs for protos all the time with nothing but a hot
> air
> >gun...
> >
> >BGAs are easier than fine pitch QFP to solder (though difficult to salvage if
> >done wrong...)
> >
> >Peter Wallace
> >
> >
> >
> >
>

Peter Wallace
Mesa Electronics
Received on Thu Apr 25 2002 - 18:29:13 BST