Tobias,
Micro stencils are used as a precaution for coplanarity issues related to
the PCB and BGA. 95% percent of the time, flux only, is adequate. We were
typically applying paste to the land pattern on the PCB but have recently
converted to applying paste to the spheres on the BGA. This was because our
customers were not willing to provide a .100" keep out area around the BGA.
For CBGA's, the solder spheres do not reflow. You will have to apply solder
paste to attach these devices to the PCB.
Regards,
Rey Sosa
Pentagon EMS
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Tobias.Chang
Sent: Tuesday, November 19, 2002 8:42 AM
To: [log in to unmask]
Subject: [TN] BGA Installation
Hello to everyone,
IPC 7711, #5.7.1 and #5.7.2 is about using wire solder, or solder paste to
prefill lands for BGA/CSP Installation.
I was just wondering if its standard practice to use a soldering iron/solder
wire to melt little blobs of solder onto the PCB before placing a BGA for
rework...maybe I'm not understanding the concept of pre-fillnig lands. And
I was also wondering if this "prefill" procedure is used only when placing
NEW BGA chips, or if it would apply if you take a chip off, and try and
place that same one back one without fully reballing it.
And I was also wondering if there are any comments about installing BGA
chips during rework, whether its better to use stencils of some sort to put
paste between the chip and the board, or if just flux will do. And if
stencils are the way to go, if you would recommend a stencil that puts paste
onto the chip, or if the paste goes on the board.
Personally from what I understand, replacing a BGA works just fine if you
use tacky flux and then put the BGA in the rework station. Not sure why
there is even a market for BGA rework stencils.
Thanks to all those that reply... =)
Toby
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