I'm also for the test coupon and always recommended at least 
half-a-dozen (preferably more) holes of each diameter, with separate 
daisy-chaining for each diameter. A single hole test is statistically 
invalid, no matter which test is done. I measured the resistance of each 
chain and occasionally did a burn-out test by applying a small voltage 
and ramping up the current until one hole burnt out, in a fume cupboard. 
This is guaranteed to weed out weak holes, due to poor drilling; even 
almost invisible faults by other methods would have fusing currents 
dropping by several amps. The coupons can also be used for X-sectioning, 
of course.

Brian

Hfjord wrote:
> Gosh! Where did I get that from? Has nothing to do with Uranium. I mean 
> My two rems.
> 
> -----Ursprungligt meddelande-----
> Från: Hfjord [mailto:[log in to unmask]] 
> Skickat: den 13 oktober 2007 22:52
> Till: 'TechNet E-Mail Forum'; [log in to unmask]
> Ämne: SV: [TN] URGENT HELP NEEDED:- non-destructive method for via hole
> plating thickness
> 
> Don't know if Feinfocus X-ray has enough resolution, but may be worth
> trying. A Feinfocus fitted with a Hamatsu image processor may fix it. There
> is a contrast difference between Copper and Tin/Lead.
> My two Bequerels
> /Inge
> 
> -----Ursprungligt meddelande-----
> Från: TechNet [mailto:[log in to unmask]] För [log in to unmask]
> Skickat: den 13 oktober 2007 18:27
> Till: [log in to unmask]
> Ämne: [TN] URGENT HELP NEEDED:- non-destructive method for via hole plating
> thickness
> 
> Hi to all,
>  
> Looking for service or friendly (aren't we all) PWB manu. who has the  
> capability to measure COPPER plating thickness in via holes in FINISHED
> BRD.  i.e. 
> with HASL in via holes.  NON-DESTRUCTIVE TESTING
>  
> Description of brd:-
>  
> 20 layers
> ~150 mils thick
> Via holes are 20-22 mils finished.
>  
> Required plating is 0.0015 min.
>  
> A few I have learnt about are CMI (probe inside the hole) & UPA  (resistance
> 
> measurement)
>  
> Rush
> 818-415-0030
> 
> 
> 
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