I agree there are no easy answers. However, split net and combo fixturing
open a really big hole for test escapes. If the system uses 1 test pin per
net in the fixture to detect isolation failures, there is not closed loop to
make sure the pin is contacting the net. In traditional fixtures, you have 2
or more pins on each multi-point net and if a pin is removed, bent, off
target or not functioning due to equipment problems, the board fails for
opens and is not shipped. With split net you only have this type of test if
the software places 2 pins per net and in combo testing, this is not
possible on some nets.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Jim Axton
> Sent: Monday, December 07, 1998 8:46 PM
> To: [log in to unmask]
> Subject: Re: [TN] Testing of bare PCB's with microBGA pads
>
>
> Frank,
>
> It's interesting that you are asking about the micro BGA's.....
> and the testing issues. Our company has four PCB fabrication
> facilities.... I'm responsible for the technical direction of our
> test groups.
>
> Everyone in the PCB arena is pushing the envelope when it come to
> testing BGA's.... You may solve (placing the BGA vectors to the
> test grids, .1", .08", & .07") one BGA on a test fixture, what
> happens when there are multiple BGA's? Our company has single
> density, double density, 80 mil grids & flying probe... BGA's are
> our biggest headache.
>
> Deflecting the test pin (pin tilting) out to .7" or 1.0" works as
> long as there is not another device to be tested within that
> distance. Last month approximately 73% of our product had some
> type of BGA or chip scale package. Multiple pass test fixtures
> are a way of life for us. We can perform combo testing.... solve
> as much as you can to the test grid and place the remaining test
> points on a flying probe.
>
> There is not an easy answer.......
>
> Jim Axton
> Dynamic Details, Inc
> 714-688-7388
> >>> "Winiarski, Frank" <[log in to unmask]> 12/07 7:54 AM >>>
> Our board supplier is having problems testing one of our board designs
> which have several .8mm (.031 pitch, .024 pad dia.) 144 pad and .75mm
> (.029 pitch, .016 pad dia.) 48 pad microBGA devices in the design.
>
> They claim that they have to use their Probot flying probe tester, which
> is very time consuming and very expensive.
>
> My question is: Are the microBGA designs too tight to utilize "standard"
> or even "double" density test equipment? With microBGA's becoming so
> "common" (?) there must be a way to cost effectively 100% net list test
> bare PCB's. If not, does anyone see a new/iimproved test technology on
> the horizon that does allow fast and cheaper testing of these designs,
> and when will it be available?
>
> Thanks.
>
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