Josh,

Good answer. I agree completely. One thing I'd like to mention is
that for ultra fine pitch (CSP, UFP, FC...etc.) as the circuit density
increases and the circuit width decrease (even in length) the flying
probe attributes test with one of the variables being capacitance.
The probe touches down and charges the trace. Now touch again
and detect the pF value. An exercise (I mean an EXERCISE!) I
have been through (a couple of times mind you) is that micro shorts
were not detected by two microtraces shorted. Maybe the 
threshold/tolerance of the equipment just couldn't cut it. Had to go
to full blown point to point (with all net close proximity) testing.
Too 2 wks to test 24 12X18 panels at 24 up. .002/.002 technology.
Maybe the testers have been upgraded within the last yr. I dunno.
There is some new ones out since then. The one from England
looks interesting. Until someone can prove different, I'll stick to
double density 2 fixture (point to point, pitch short to point) and
intensive AOI with reflective and flouressive in 1/10 mil res.

My .02 cents.

Have a happy Holidays

[log in to unmask]
  

===================================================
Date: Thu, 12 Dec 96 14:12:37 PST
From: <[log in to unmask]> (Josh Moody)
To: <[log in to unmask]>
Subject: re: test: FLYING PROBE VS. HARD TOOLING
Message-Id: <[log in to unmask]>
Content-Type: text/plain;
               charset=US-ASCII

The biggest difference from a pure manufacturing standpoint is that
flying probe testing takes alot of time, based on my experience
about 70 minutes per board (assume 7500 test points per board).
The benefits are that the customer does not need to pay for a fixture,
therefore for prototypes it is the best way to go.  The machines
are somewhat spendy ($300K-$400K) and require the user to be well
trained.  From PCB consumer standpoint they are a great addition to
the world of electrical test (usually costing is done on a test point 
basis - ie one test point costs $0.04).  Another side benefit is the 
ability to test finer pitch devices, PCB manufacture of 10mil pitch
has really pushed traditional ET methods into a corner.  The more 
expensive flying probe are able to do 10mil pitch.  Anyway that is my 
opinion  

Regards,
Josh Moody
Process Engineer
Merix Corp.



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