The requirements for X-outs for panelized printed boards are about as
varied as the number of customers for boards. In a past life with an
OEM, no defectives were allowed on an array. Now that I am with a
fabrication shop I have seen specifications ranging from 10% of the
boards on 10% of the arrays to no defects. Methodology for identifying
the defects is even more interesting. Defect identification ranges from
a "X", to a paper sticker over a tooling hole, and to drilling out
fiducials and coloring the boards black.
The varied specifications seem to arise from the capabilities of each
assembler's equipment capability. Some types of assembly equipment do
not have "skip cell" or auto defect sense capabilities. Some through
hole equipment rely on off line sequencers. The just in time concepts
make planning for random defects on arrays a royal pain for materials
planning.
Many fabricators offer discounted board prices for allowing defects on
arrays. IMO you are paying for the fabriactor's ability to manufacture
X square inches of board without a defect or in other words the larger
the board the lower the yield. The real deciding factor for any
assembler is the total cost of handling arrays with defective boards.
This cost is difficult to determine, but includes purchase price of
components, lost labor (and aggrivation) of handling defective images,
parts lost due to defective boards, and increased labor from handling
the extra material.
I could go on for another page or three, but this covers the basics. I
should also include the disclaimer that these opinions are definitely
mine and now those of my employer. I hhope that this was of some help.
Don Vischulis
QA Manager
ITO Industries
[log in to unmask]
[log in to unmask] 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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