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October 2001

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Subject:
From:
"Lush, Dorothy" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 15 Aug 2001 12:04:01 -0700
Content-Type:
text/plain
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text/plain (108 lines)
If the components are small chip parts they are making little mosaic pendant
jewelry.
But seriously, fallout takes a number of forms and part of this is because
of people who are not paid to think (PNPTT). Every reel has a leader at the
beginning and the end of the reel of empty pockets that usually wraps around
the reel at least once. Some PNPTT's count the empty and loaded pockets
which makes their count wrong in many cases. PNPTT's can be located at the
OEM and/or the CM. Of course, suppliers/manufacturers never miscount.

SMD feeders have at least one inch of strip/carrier where the top tape is
pulled back exposing the parts to a high chance of loss especially when they
are small components. Loading/setting-up the feeder is done at setup which
is some distance in time and space from production.

If a strip of parts is cut sometimes the cutting tool cuts into a pocket
leaving the back door wide open and the part is lost on some floor somewhere
along the way.

Everytime the placement machine stops and a particular feeder is pulled out
and checked is another opportunity to lose parts. I have found this occurs
more frequently with plastic carriers than with paper carriers on the
smaller chip parts. It seems the tape on top has a glue that is either
weaker and breaks 10 times more often or the glue is stronger or stickier
(so it sticks to the feeder when pulled back) and the tape breaks therefore
cannot be pulled back to expose the next part and the machine stops.

Placement machines will reject parts and lose parts for various good and bad
reasons.

Bill of materials (BOM's) are sometimes off in their quantities (this
happens much more in prototype and the transistion to full production than
in full production).

Rework needs extra parts. The smaller the part and the less reworkable the
part the more extra parts you need.

IC type parts with leads tend to get damaged at the beginning of a strip
with no empty leader pockets.

Bad layout will result in many more defects: lost part, tombstone,
misaligned, bridging. If you couple this with nonreworkable part you will
need extra parts.

I was an engineer on an account that had some RF boards. After the first
disaster I ordered my own attrition that was based on the part cost,
qty/assembly and likelyhood of the part to get lost or come in damaged.
Frankly, the time lost ordering parts and the line down time (somewhere
between 2K and 6K/hour, depending) waiting for parts pays for most
attrition.

The most difficult thing here is that most component buyers can only order
for a build qty with no attrition and this all goes back to software
programs and their inflexability.

Dorothy Lush

> ----------
> From:         Rick Howieson[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.
> Sent:         Wednesday, August 15, 2001 6:20 AM
> To:   [log in to unmask]
> Subject:      Fallout
>
> Our purchasing department believes people are taking components home and
> making necklaces...hehehe. So my question, what is the typical
> loss/fallout
> of smt components, on reel, does one see?
> Thanks,
> Rick Howieson
> Delta Group Electronics, Inc.
>
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