HI Tom,
IPC-7095 "Design and Assembly Process Implementation
for BGAs", (Interim Final Draft), section 6.1.2,
states: "In general, an minimum of 3.125 mm component
keepout (i.e., the nominal distance between the body
of the component and the body of the neighboring
component) is needed so that both the nozzle clearance
requirement and the muni-stencil requirement can be
met."
Note: 3.125 mm is approx. 1.230"
I agree with Steve, the nozzle size on your rework
machine will make the difference. I've used several
different machines in the past, and nozzle sizes (foot
prints) differ between manufactures, and nozzle sizes
may differ within manufactures, (depending on their
state of evolution at the time.)
If you are using solder paste and a stencil, the type
and thickness of stencil will also be a consideration.
(Thicker stencils don't require as much solid border,
thus less "keep out area".) We have stopped using
stencils that use a holder to support the stencil, and
use a flat, narrow border stencil. We find they
consume less room
When I was able to work with the design engineer, I'd
beg for 0.200' keep out. Sometimes I'd get it. The
last IPC meeting I attended, there were attendees who
only wanted 0.100". They must have machines with thin
wall nozzles. If you have access to design engineers,
request space under the BGA so you can support the PCB
during rework. Supporting sagging PCBs during rework
has been a challenge for us in the past, because of a
high concentration of differing height components.
Note: We have had to remove some neighboring
components before reworking customer's PCBs with BGAs,
so we could gain access with our nozzle. Not only due
to keep out invasion, but due to component height
interfering with the machine prism extension.
If you are going to be at APEX in Long Beach, CA next
week I invite you to attend the BGA Workshop, by our
President, Charley Dennehy. He will gladly answer any
of your questions in more detail.
I hope this helps.
thanx
Bill
--- Thomas Han <[log in to unmask]> wrote:
> Hi all,
> What is a general quideline in perimeter clearance
> around BGAs for Rework.
> Thanks in Advance.
>
> Tom
>
>
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Circuit Technology Center
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