Eva,

 How does any trained eye detect when 0402 resistors had the wrong value
stuffed? Or maybe the tan ceramic caps are mixed? (Neither of these have any
markings.) Or LED orientations? 

 I think this kind of stuff is impossible by eye. 

 I have also been hearing that visual inspection is good for low volume but
not good for higher volume. In my mind that is nonsense. I think it all
comes down to the probability of a human missing an inspection point. It
seems that 1 : 10K is a best case miss rate. But a board has THOUSANDS of
inspections points. With a large run I can see fatigue setting in and the
miss ratios can get much worse. But for small quantities there is still a
percentage of missed inspections points. I would ask: What time do you
perform visual inspection? When are operators less fatigued?

I am not suggestion DO NOT INSPECT. It is important to visually inspect. My
experience includes running a small business where I used ICT, I am a big
believer in using ICT. But even ICT will flag a board as good if a joint is
not soldered but currently making contact. Only a visual inspection will see
that. But, in general, when the ICT tester turns on the GREEN light you
might as well ship the unit because it is VERY good. 

 We do our soldering inspection before ICT. Soldering quality is often
global in nature. The most evil process failure was too little paste at a
point. Bent leads on an Gull Wing parts were also a great evil. But the Rs,
Cs and many L values are tested and powered on ICT tests ring out many IC
open failures.

When people tell me they want "Real High Quality" in final product and they
focus on human inspection I just don't buy it. 

 Bob



 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eva J
Sent: Wednesday, October 23, 2013 9:01 AM
To: [log in to unmask]
Subject: Re: [TN] Inspecting Class 3 Assemblies

Bob,
We 100% inspect all product (low volume, high mix, complex designs, class 2
and 3) received from various contract manufacturers and we consistently
identify defects that the contract manufacturer's AOI and X-Ray missed
(Examples: component cant, component damage, laminate issues, solder volume,
missing components, solder balls violating minimum electrical clearance,
head in pillow...........). There is no substitute for the trained eye.

Eva J


On Wed, Oct 23, 2013 at 8:26 AM, Ioan Tempea <[log in to unmask]
> wrote:

> Bob,
>
> For class 3 boards of that complexity you cannot rely on visual 
> inspection to weed out 100% of the quality problems! What you want is 
> visual + AOI + X-Ray and also functional test. No functional test, no 
> certainty that you've caught everything. On top of it, testing has to 
> have a proper coverage.
> Then, you'll need some screening, like thermal shock or burn-in, in 
> order to catch infant mortality issues that get away even after having 
> done all the above.
>
> And this will, eventually, ensure good quality, which means good 
> workmanship. But things don't have to stop here either, as you have no 
> idea about the long term reliability of the product, which is 
> intimately related to design (Werner would have had many things to say
here).
> So you'll need to wrap it up with proper ESS screening.
>
> But now that I'm done ranting, I see your mandate is to perform 
> inspection only. Maybe you could get away with the reliability part, 
> but I don't believe you can commit to properly fulfilling your mandate 
> without functional test and infant mortality screening. Believe me, 
> I've been down that path. 4000 parts and this complexity means that, 
> if you judge based on DPMO, there is at least one defect on each board.
Try and find it!
>
> To end on a sweeter note, of course you could commit to the task, if 
> not you, somebody else will, but make sure the contract has provisions 
> that will allow your company to fight the endless spiral of customer
returns.
>
> Regards,
>
> Ioan Tempea
>
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> -----Message d'origine-----
> De : TechNet [mailto:[log in to unmask]] De la part de Bob Wettermann 
> Envoyé : Tuesday, October 22, 2013 4:16 PM À : [log in to unmask] Objet : 
> [TN] Inspecting Class 3 Assemblies
>
> Dear Technetters:
>
> I think these things come in bunches.
>
> We are being asked to perform contract inspection of Class 3 medical PCBs.
> I would categorize this board as "high complexity" with BGAs, UHDI 
> connectors, 0201s and about 4,000 parts. There are 100+ boards.
>
> Obviously performing this manually will would take many hours and 
> based on previous experience, be only 80% effective using a single set of
eyes.
>
> So my question for those of you building IPC-A-610 Class 3 product for 
> mil, aerospace or medical is how do you insure that class 3 solder 
> joint and other inspection criteria are met? The AOI we have will not 
> do the trick!
> The leadless devices and BGAs we will inspect via XRAY. Other ideas 
> for doing this "offline"?
>
> Bob W/BEST
>
>
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