Arlene, 

I too have used +/-10% for PCB finished thickness tolerance for the past 25 years. That was passed down to me from the PCB manufacturer's that I have used. 

The IPC-2221A section 5.4.1 "Dimensions and Tolerances" refers to the new IPC-2615 for Geometric Dimensioning and Tolerancing (GDAT). Unfortunately I have most of the 2610 series except 2615, so I can't verify if what you're looking for is in there, but here is the list for the IPC-2610 series - 

IPC-2611 - Generic Specification
 
IPC-2611 - Generic Requirements for Electronic Product Documentation

IPC-2612 - Sectional Requirements for Electronic Diagramming Documentation (Schematic and Logic Descriptions)

IPC-2613 - Sectional Requirements for Assembly Documentation (Electronic Printed Board and Module Assembly Descriptions)

IPC-2614 - Sectional Requirements for Board Fabrication Documentation (Printed Circuit board Description Including Embedded Passives)

IPC-2615 - Sectional Requirements for Dimensions and Tolerances

IPC-2616 - Sectional Requirements for Electrical and Mechanical Part Descriptions (Specification and Source Control Part Descriptions)

IPC-2617 - Sectional Requirements for Discrete Wiring Documentation (Wire harness, Point to Point and Flexible Cable Descriptions)

IPC-2618 - Sectional Requirements for Bill of Material Documentation (Complete Listing of Parts, Materials, and Procurement Documents)


Tom



-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Arlene Fox
Sent: Friday, May 20, 2011 10:04 AM
To: [log in to unmask]
Subject: [DC] PCB thickness standard

Hi all,

Can somebody point me to the IPC standard that defines the tolerance for a pcb's finished thickness?  I always use +/- 10% but I haven't been able to locate the standard.

Thanks






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