Thornton,
I wouldn't load a BGA without solder paste on to a ENIG finished
PCB. Even though the gold is probably pretty thin, without the additional
solder from the paste, you're taking a chance of gold embrittlement.
I know that there are those that say one only needs flux for BGA rework
if the BGA has eutectic spheres, but I feel that the extra volume of solder
from the paste gives the BGA more stand-off, thus more reliable.
As for a mini-stencil a US company called Circuit Technology Center
makes something called "Flextac Stencils". I've used them on numerous
occasions, the most recent was when I had to rework a 676-ball, 1mm pitch
Xilinx BGA.
The Flextac stencils can be obtained from:
Intertronics
Unit 17, Station Field Industrial Estate
Banbury Road
Kidlington
Oxfordshire
OX5 1JD
England
+44 (0) 1865 842842 Phone
+44 (0) 1865 842172 FAX
Here's a link to Intertronics web site about them:
http://www.intertronics.co.uk/products/flextac.htm
Here's another link to all the BGA patterns available as the Intertronics
wb page didn't seem to show all the different pattuerns that are available.
http://www.circuittechctr.com/products/201-3120s.shtml
Another product that is fairly new on the market for BGA rework is
something
called "StencilQuik". It's basically a polyimide, or kapton, stencil that
is placed
over the BGA footprint, paste stenciled into the apertures, the BGA placed
(can
literally be done by hand), and then the BGA reflowed. The StencilQuik
stencil
then becomes a permanent part of the assembly.
I have no direct experience with StencilQuik, but it does seem rather
interesting.
Here's a link to it:
http://solder.net/stencilquik/default.asp
Kind regards,
-Steve Gregory-
|---------+---------------------------->
| | Thornton White |
| | <thornton.white@C|
| | EMTRON.COM> |
| | Sent by: TechNet |
| | <[log in to unmask]>|
| | |
| | |
| | 03/14/2005 09:25 |
| | AM |
| | Please respond to|
| | TechNet E-Mail |
| | Forum; Please |
| | respond to |
| | Thornton White |
| | |
|---------+---------------------------->
>--------------------------------------------------------------------------------------------------------------|
| |
| To: [log in to unmask] |
| cc: |
| Subject: [TN] |
>--------------------------------------------------------------------------------------------------------------|
Hi All.
We have a customer who wants us to place BGA's for them on otherwise
comletely loaded PCB's.
Problem is, the BGA apertures were missed from their stencil.
Is it at all possible to load a BGA straight on to an unpasted (gold
finish)
card? What are the quality implications?
Assuming the answer to above is NO, does anyone have UK contacts for BGA
mini-stencils
Any advice would be appreciated.
Thanks in advance.
Thornton
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