If this is true, how do you call out the finished PCB thickness? what kind of tolerance are you using to insure the part meets the print? Are Assembly houses (CM's) accepting boards that do not meet the thickness requirements called on the print or are they asking designers to adjust the tolerances so boards will meet the new thickness requirements?

I thought the board suppliers were supposed to make adjustments to the stack up to meet the final thickness I called out on the print. The only exception would be when the stack up was design dependent as noted in the fabrication notes. Is this no longer the case? If it's not, how do I insure there is not going to be a stack up issue with my board thickness tolerances and my enclosure tolerances? Are designers expected to submit the files, get feedback from the board house and adjust the final thickness of the board? If we were to send this to another  board house should I expect the finished thickness to change again?

Ted T

-----Original Message-----
From: Yoch, Brian [mailto:[log in to unmask]] 
Sent: Friday, November 22, 2013 11:09 AM
To: TechNet E-Mail Forum; Tontis, Theodore J
Subject: RE: PCB stack up question

I used to sweat the stackup differences between vendors. But after talking to several reps face to face and over the phone I am no longer too attached to my stackup. The stackup that we call out is nothing more than a guideline for the CM to reference, because no 2 CMs will have the exact same process.

Brian Y. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Theodore J Tontis
Sent: Friday, November 22, 2013 10:11 AM
To: [log in to unmask]
Subject: [TN] PCB stack up question

I have a 6 layer stack up specified on my gerbers as:

0.0004 mil solder mask
0.0014 mil top layer 1oz copper
0.0086 mil 2 X 2116 prepreg
0.0014 mil inner 1 1oz copper
0.0140 mil core
0.0014 mil inner 2 1oz copper
0.0086 mil 2 X 2116 prepreg
0.0014 mil inner 3 1oz copper
0.0140 mil core
0.0014 mil inner 4 1oz copper
0.0086 mil 2 X 2116 prepreg
0.0014 mil bottom layer 1oz copper
0.0004 mil solder mask

0.0620 mil total stack up +/- 0.006

Our CM's vendor is requesting I change either
A: adjust the 14mil core to 12mil to meet 62±6mil finished thickness.
B: relax the finished thickness to 65±6mil..
C: control the board thickness with 62±6mil exclude the solder mask thickness.

Their stack up is as follows:

0.0005 mil solder mask
0.0020 mil top layer 1oz copper
0.0091 mil 2 X 2116 prepreg
0.0012 mil inner 1 1oz copper
0.0142 mil core
0.0012 mil inner 2 1oz copper
0.0085 mil 2 X 2116 prepreg
0.0012 mil inner 3 1oz copper
0.0142 mil core
0.0012 mil inner 4 1oz copper
0.0091 mil 2 X 2116 prepreg
0.0020 mil bottom layer 1oz copper
0.0005 mil solder mask

0.0649 mil total stack up +/- 0.006

I got my stack up from a local vendor I've worked with in the past.
Our CM has measured some of their bare boards at 0.070 and 0.071 mil thick.

Which stack up is correct or am I missing something important?


Ted T.


Theodore J. Tontis CID
Senior Manufacturing Engineer
[cid:[log in to unmask]]<http://www.eaton.com/>
11131 Adams Road
Franksville, WI 53126
Office 262-835-1552
Cell 262-510-3145
Fax 262-835-1544


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