I can tell you I'm happy, ONLY because this confirms what we've always 
     felt.  I'm not happy about it as a board designer and user.  This 
     means that when we determine line widths for current carrying 
     capability we have to plan with a copper thickness of 80% of nominal.  
     That's because the copper foil fabricator can steal (yes steal) 10% of 
     the thickness from me, and the IPC allows the PWB fabricator to remove 
     up to 10% of the thickness too (understandable loss)!!!  So, all 
     totalled, I have to accommodate a 20% loss in current carrying 
     capability.
     
     Also, it's good to know that the copper foil manufacturers are capable 
     of manufacturing a foil with a 5 % tolerance.  Maybe it's time to 
     change IPC-MF-150 to reflect what foil manufacturers are capable of.  
     While we're at it, let's get that 2-3% minimum elongation corrected 
     too.
     
     


______________________________ Reply Separator _________________________________
Subject: [TN] ...copper foil thickness...
Author:  "TechNet E-Mail Forum." <[log in to unmask]> at smtp
Date:    3/26/98 10:08 PM


Hi Mate,
     
it worldwide praxis to make copper foil 10% below its weight/thickness. 
There reasons are quite simple. Both parties are happy. The Cu maker can 
make 10% more in the same time and a customer gets 10% more area. It's a 
win/win situation. It's also within IPC standard.
     
It doesn't work as well for 18µ, since it's more difficult to control. If 
your consumtion is large you can ask them to make it exactly 35µ - or 
whatever you need.
     
regards
     
Jens Behrens
     
     
     
>We are facing a perpetual problem with the supply of copper foil thickness. 
>
>The vendors are allway sending material thinner than the standard. This 
>cause, after the chemical processes of manufacturing, a copper layer below 
>the limit acceptable by the customer.
>
>As an example: The metric equivalent for 2 oz. is 610 grams per sqr m. The 
>10% tolerance  allow thickness between 549 and 671 grams.
>
>One of the suppliers admit that he supply material between 550 and 580 
>grams (which is -10% to -5%).
>
>The following are quotes from his letter: 
>
>"This is common practice, indeed all of our customers use the typical range 
> of 550 to 580 grams per sqr m."
>
>"I can assure you that the material produced at the lower substance weight 
>perform exellently with no detrimental effect for the reduced substance 
>weight".
>
>The same problem exist, as well, in laminates. 
>
>Our practice is that the copper weight is usualy better in 0.5 oz but start 
>to be marginal on heavier weight.
>
>I will appreciate your practice and comments. 
>
>
>Hillel Dzigan - Quality Manager
>Eltek Ltd.
>Phone +972-3-939-5022, Fax +972-3-930-9581 
>P.O. Box 159, Petach-Tikva 49101, ISRAEL
     
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