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From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 12 Dec 2013 14:52:37 +0000
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I know it ha'pence, but we've all got to quit shilling the quid,  Bob.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Thursday, December 12, 2013 8:40 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-6012C Total Cu thickness

Yes, everything is transferring to UK currency. It gives a whole new meaning to pound the keys.
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Don Vischulis
Sent: Thursday, December 12, 2013 5:13 AM
To: [log in to unmask]
Subject: Re: [TN] IPC-6012C Total Cu thickness

To quote one famous expert, "it depends".  The board designer understands the needs of the board.  The thickness specification needs to consider the at least the following:  copper surface thickness, through hole copper thickness, plating ratio for through hole vs. surface plating (which usually plates more on the surface than in the hole), and line width and spacing.  All of these factors affect the performance and the producibility of the board.  In some cases the cost is also affected.

Just my $0.02.  (Interesting...just noticed that the iPad doesn't have the cents symbol...guess that means that the penny is really on the way out)

Don Vischulis

Sent from my iPad

> On Dec 11, 2013, at 7:19 PM, Bernard <[log in to unmask]> wrote:
> 
> Hi Raye----
> While it may be no comfort because I'm out of my area of confidence, I 
> believe you are correct.  If the starting thickness is to be a 
> requirement, the only way to inspect would be to get a coupon from the 
> lot number----- so it seems to me.
> Otherwise, the overall thickness should be specified as the 
> requirement.
> Enjoy!!!
> Bernie
> 
>> On 12/11/2013 4:48 PM, Rivera, Raye wrote:
>> Hi Bernard,
>> 
>> As a general rule, copper is copper. On this specific board our engineering team confirmed that the ratio of foil to plate does not matter.  While I am no expert, the only time I can think of that it might matter is in traces for very high frequency signals.  On these even the surface roughness of the trace and the cross-sectional profile of the trace can matter.
>> 
>> Here is another consideration.  We determined that the foil layer the PCB fabricator used was less than 1/2 oz based on a microsection.  The PCB fabricator tell us that they did start with 1/2 oz copper and intentionally reduced it to 3/8 oz chemically. If they didn't do this,  by the time they got the right amount of plating in the through holes, they would have up to 1.7 oz surface copper.  For reasons I don't fully understand they would not be able to hold our trace and space requirements when they etched the outer layer traces.
>> 
>> I have always thought a microsection shows the thickness of the starting foil. Apparently it only shows the thickness of what remains of the starting foil. If we can't measure it, why should we state a minimum starting thickness for the foil in the standard? I can see the value of including it in table 3-12 as a general guideline, but it does read as if it is a requirement.
>> 
>> Best regards,
>> Raye Rivera
>>  
>> 
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Bernard
>> Sent: Wednesday, December 11, 2013 12:38 PM
>> To: [log in to unmask]
>> Subject: Re: [TN] IPC-6012C Total Cu thickness
>> 
>> I ask this question just out of curiosity----- Does the cu/plated metal ratio affect in any way the signal transfer rate or electrical characteristics????  If no---- all seems academic beyond the total thickness.  If yes, then min cu seems appropriate.
>> Bernie Kessler
>> 
>>> On 12/11/2013 12:23 PM, Grunde Gjertsen wrote:
>>> Those tables are very educative when explaining to QA and design people why final copper thickness is what it is in relation to base copper and class and should be left well alone in my opinion, they are not that difficult to understand if you know a bit about PCB manufacture.
>>> At least over here people in the industry is getting more removed from PCB manufacture since so many factories has closed down and production gone to far east, so to have the standards actually explaining stuff like that and not simply stating requirements is not a bad thing.
>>> 
>>> Rgds
>>> Grunde
>>> 

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