Hi Ken,

        The explanations defining true position in the other responses are
     right on, but as to why .006?  It's driven by the tolerances that the
     automatic leaded component insertion machinery will tolerate in the
     assembly operation.  Your typical well maintained drilling equipment
     can achieve this if all holes are drilled only in a primary drilling
     operation.  However, you mentioned .010" vias.  You will likely not
     stay within the .006" true position, but this will not likely be an
     issue if the required annular ring is met.

        As for front to back registration, it's really probably one of this
     industry's top five useless requirements.  Excepting some very rare
     situations where electrical properties associated with adjacent layers
     are affected, there are no function or reliability issues associated
     with front to back registration per se.  The annular ring and minimum
     hole-to-copper are what decides the degree of misregistration that you
     genuinely can tolerate.

     Mike Mikucki



______________________________ Reply Separator _________________________________
Subject: [TN] True Position and Registration on Fab
Author:  Ken Patel <[log in to unmask]> at SMTPLink-Hadco
Date:    11/18/98 5:03 PM


Fab Gurus,
We are designing board with a 40 mil BGAs first time and the fab will be
having 10 mil plated finished holes on it. I opened up an old existing
drawing of different non-BGA board and now I have couple of questions after
reading my fab drawing notes.

(1) Fab note: All holes to be within .006" true position on the diameter
with respect to original data.
Question: What is true position and why .006"? How to decide this number?

(2) Registration: Front to back to be within  +/-.005". Can anyone explain
what is registration and why .005"? Who can decide this #, is it fab house's
processing capability?

re,
Ken Patel
______________________________________________________
Ken Patel                       Phone:  (408) 490-6804
1708 McCarthy Blvd.             Fax:    (408) 490-6859
Milpitas, CA 95035              Beeper: (888) 769-1808

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text
in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for
additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700
ext.312
################################################################

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################