Guy Ramsey
Senior Technician / Instructor
The is no real consensus on voids. These are my comments and my
opinion based on observations and requests for help that we have received over
the past two years. Variation is bad and so is non-wetting. For single
large voids verify wetting. If we see multiple voids in some balls and none in
others we have variation.
As the balls get smaller, voids have a
larger influence on the strength of the interconnect, at the same time the
package demands more from the interconnect. CSP require better control of
voids, not less.
A longer lower soak with a quicker ramp into reflow may
help. Some packages tend to warp during this transition if the rate is too high.
Changes in ramp rate near reflow temperatures can cause voids. Multiple reflows
can induce voids (BGAS on both sides).
Some pastes are more prone
to produce voids than others. Work with your paste supplier.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf
Of Håkan Törnqvist (EMW)
> Sent: Thursday, May 16, 2002 5:10 AM
>
To: [log in to unmask]
> Subject: [TN] Voids in fine-pitch BGAs after
reflow
>
>
> Hi,
>
> Does anyone know of criteria
for voiding in fine-pitch BGAs after reflow?
>
> IPC-7095 suggests
for BGA:
>
> Class I: 60% of dia = 36% of area
> Class II: 45%
of dia = 20.25% of area
> Class III: 30% of dia = 9% of
area
>
> Does this apply to fine-pitch components as well? Are there
any
> theories indicating that one can tolerate higher percentage
as
> the balls get smaller?
>
> Thanks,
> Hakan
Tornqvist