Dave,
Expected losses depend on a number of factors:-
1. If you don't leave a leader tape on reels each time you unload from the
machine, you will lose the number of components contained in the lead-in
distance. This is typically about 7 inches - divide by the component pitch
on the tape and you have your attrition qty for every time you re-load the
reel to the machine.
2. Handling - if your IC's, etc are well handled and in good condition,
there should be very little or no attrition. If badly handled or of poor
quality, the machine may reject any number of components on the grounds of
poor lead alignment. Most machines just chuck rejects down a chute, where
they are further damaged, but it is possible to arrange for the rejects to
be collected nicely without further damage. These can then be inspected and
may be useable if hand soldered, for example instead - the economy of this
depends on component cost/availability versus recovery/inspection/recycling
costs.
3. First article inspection - assembly houses usually do a dummy run the
first time they build a board to check and fine tune the P&P programming.
This uses one complete set of components of that board, which is often
populated onto a PCB wrapped in sticky film. The components stick to the
film, but the PCB itself is not affected. For aerospace/military boards
where components are expensive, the active components are recovered, but
the passives are usually not worth the cost of recovery so are lost.
P&P attrition is almost a case of "how long is a piece of string", but the
above may help you to gauge rougly how many extra components you will have
to allow for, depending on your situation. With a little planning and
forethought, very few components need be lost, but the potential to lose
quite a lot is there if care isn't taken and you don't go through the
process steps in advance to see where losses can occur.
Good Luck!
Peter Duncan
Dave Snyder
<[log in to unmask] To: [log in to unmask]
COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
Sent by: Aero/ST Group)
TechNet Subject: [TN] SMT Component Loss Percentages
<[log in to unmask]
ORG>
01/03/02
03:43 AM
Please
respond to
"TechNet
E-Mail
Forum."
What is the expected part loss in the pick and place process? I assume the
percentages are different depending on the type of part and size. It's
probably is much better if the lots are very large, however we manufacture
board assemblies in small lots (50-200). Is there an IPC document that
lists
"normal" levels or guidelines? Any help would be greatly appreciated, even
wild guesses.
Thanks
Dave Snyder
Manufacturing Engineering Manager
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