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]
[log in to unmask]
11/08/98 15.26
Please respond to [log in to unmask]
To: Mike Mancini/Italy/IBM@IBMIT, [log in to unmask]
cc:
Subject: Re: [TN] Magnification IPC-A-600
All,
The question was about the interprtation of the allowance to go to 40X to
verify a defect seen at 1.75X
Measurement oif the size of the defect has nothing to do with the higher
magnification allowance. The spec. allows going up to 40X so that the
inspector may verify that his defect is really a defect. Often at 1.75X
shadows at a nodule, small pits or roughness etc.may appear to be a defect,
but when a better viewing at up to 40X is used, it is found to be acceptable.
Phil Hinton
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