Phil,

We did dye penetrant testing of plastic BGAs a few years ago. First we
created a dam around the BGA and filled it with the dye penetrant. We put
the board in a vacuum chamber and decreased the pressure until the dye
penetrant just was about to start boil and then increased the pressure to
room pressure again. Thereby, we got better penetration by the dye. This
procedure should be executed as quickly as possible. Otherwise, too much
solvent will be evaporated causing an increase of the viscosity of the dye
penetrant.

The most difficult part was to remove the BGAs. If we removed the components
by bending the boards, the solder pads were teared away from the laminate if
the cracks were not enough large. After some testing we found a solution.
The trick was to let the solder creep when you remove the package. We
achieved that by gluing a steel hook on top of the package with a
high-strength epoxy (make sure that the surface is clean before you apply
the glue) and a weight of 10 kg was then attached to the hook, applying a
vertical pull force. With time, sometimes for several hours, and in some
cases with a little help from elevating the temperature to approximately 85
degree C, all BGAs could be removed in a consistent way.

The results were reported at SMI in 1997 ("Reliability of Ball Grid Array
Packages in an Automotive Environment", Proc. Surface Mount International,
1997, pp. 85-92).

Hope this will help you.

Per-Erik Tegehall
IVF
SWEDEN

> ----------
>
>
> Does anyone have a good procedure that I could use to apply dye penetrant
> to detect cracks in BGA connections?
> Or is this type of testing better off left to the experts at a test lab?
>
> We have some test vehicle circuit cards which are failing electrically
> test
> after subjecting them to thermal shock cycles.
>
> The failures are no longer intermittent at room temperature so I don't
> expect to find just microcracking, but I don't want to just rip the
> component off either.
>
> These are test vehicles on which we hoped to determine how close to a BGA
> that hardware (screws) attaching the circuit card to a chassis can be
> placed without deleterious effects as well as to determine the effect of a
> compressive thermal transfer sheet material on the BGA connections.
>
> Any information would be appreciated.
>
> Phil Bavaro
>
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