>Date: Thu, 30 Jan 1997 07:35:35
>To: [log in to unmask]
>From: Neil Maloney <[log in to unmask]>
>Subject: Re: FAB - Defective units on panelized PWBs
>
>Jennifer, 
>  I know the problem and a possible solution.
>In our plant we use a Mydata TP9-2 PNP which has a "bad board indicator"
feature.  Each PWB on the panel has a "bad board fiducal" placed somewhere
central (generally in the center of a large component, like a QFP)  If the
PNP vision system sees contrast around the fiducal, if surmises that the PWB
is good. On the other hand, if it sees no contrast around the location (as
if a white sticker were placed over the spot) it declares the PWB bad and
places only to the "good" boards on the panel.  Automatic.
>   Before each panel is put into production, our operator places a VERY
THIN white label over the bad board fiducal. It doesn't even HAVE to be a
fiducal, any large pad or contrasting mark will do.
>
>Down, dirty, and cheap--but effective.
>
>The thickness of the label is very important, as it will be stuck to the
panel throughout the process, including screen printing. Also there may be
ESD issues here.
>  
>If your PNP can do this, (most of them can, I believe) no problem.
>
>For the other question, I make PCMCIA adapters in an 8-up panel (4-layer,
20 mil pitch, .002in thick). Because of the tight parameters, board house
loses some out (especially in E.T.) In my case I get 1 or 2 bad units on at
least 10% all the panels in the lot. Not much fun, but do-able.
>
>Neil Maloney
>Contemporary Control Systems, Inc
>[log in to unmask]
>
>
>At 01:41 PM 1/29/97 -0500, you wrote:
>>Is there an industry standard for allowable defects, or x-outs, for panelized 
>>PWBs?  For instance, if a panel is 8-up, and there are 625 panels in the lot 
>>(5000 pcs. total in the lot), what is a reasonable defect rate? A PWB 
>>manufacturer has suggested 1 PWB per panel, and a max. of 10% of the
panels in 
>>the lot.  For this example, that allows 62 panels with an x-out, which seems 
>>excessive.  The problem with the x-out is that the automatic pick and place 
>>equipment will stuff the bad PWB unless manually overridden, so there will be 
>>scrap component costs.   Comments, please.
>>
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>>
>

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