Mike,

The last three paragraphs of section 1.5 in IPC-A-600 spell out the
magnification to be used.  The wording is somewhat confusing.  However,
the intent is to require a minimum magnification of 1.75X for visual
inspection.  The part is acceptable if no defects are seen at this
magnification.  Magnifications above that - usually starting at 10X are
used for referee IF a potential defect is observed at 1.75X.  Paragraph
3.3 of IPC-6012 (IPC-6012 would normally be the actual fabrication
specification) supports this  interpretation with a more clearly worded
requirement.

Of course requirements specified by the customer can change the
magnification you would use.


Jay Soderberg

LEGAL NOTICE:  The above opinions are my own and no way reflect the
opinions of the owners or management of this radio station.


>
>
> Subject: Re: Magnification IPC-A-600
> Date: Wed, 12 Aug 1998 16:26:51 +0000
> From: Mike Mancini <[log in to unmask]>
> Phil,
> first of all thank you for your answer.
> Any way let me try to be more specific on my question:
>
> I'm a Quality Mgr.; so, I've the commitment to assure
> to my Customer that my product meets his requirements.
> My Customer's requirement for the "gold printed contacts"
> of my printed boards is to meet the IPC std.
> Well, based on the above, I need to set up  an outgoing
> Visual Inspection on my product capable to verify that my
> product meet the IPC std.
> Now, based on how I interpret the IPC-A-600 I can set up
> at least two types of procedures for my QC inspector:
>
> a) - First I give my inspector a 1.75 X magnification lens.
>      - Then I also give him a microscope up to 40 X.
>      - After that I give him the disposition to inspect the
>        products using the 1.75 X lens for a go/no go inspection
>        and isolate only those products where he has some doubt
>        for a potential defect.
>      - Finally the operator re-inspect the products previously
>        isolated, using the microscope, to determine the real
>        defective ones, against the criteria of par. 2.7.1
>
> b) -  I define as inspection tool "only" a microscope up to 40 X.
>      - Then I ask the QC to inspect the product using the microscope
>         and assess that all the potential defects meet the criteria
>         of par. 2.7.1
>
> Now, you can easily understand that the two methodologies
> have a very big difference in terms of work load for inspection
> and also in terms of efficiency.
> Using the a), practically, the inspector has to evaluate and
> asses only those potential defects that are enough apparent
> to be seen at 1.75 X. If you look at the criteria of par. 2.7.1 you'll
> see that, for example, an exposed copper spot is acceptable if
> smaller than 0.13 mm in length. Now, I'm pretty sure that at least
> 50 % of the time nobody can see at 1.75 X an exposed copper
> of this dimension.
>
> While using the b) I'm forcing the operator to use always a
> magnification (I would say 10 X as starting point) such as we
> are 100 % sure that he can detect this size of defect.
>
> In conclusion I have to decide if the inspection has to be done
> at 1.75 X or at 10 X; and this make a lot of difference.
>
> Thanks again for any more contribution to this discussion.
>
>
> Best Rgds
> Tel. (039) 6004432
> e.mail: Mike Mancini/italy/IBM@IBMIT
> internet: [log in to unmask]
>
>

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