Andy,

     This formula fails to take into account the fact that annular ring for
     inner layers is measured from the edge of  the drilled hole to the
     edge of the pad.  Consequently, any formula for determining annular
     ring must start with the drilled hole size (typically .005" larger
     than finished hole size).  The mfg tolerance adder of .010" is also on
     the tight side.  This may be fine for outer layers, but a more typical
     number is .014" for inners.  .010" is certainly achievable, but most
     likely will require smaller panel sizes and limited production levels.
      In addition, unless things have changed since I've dealt with
     military product, the minimum annular ring is .002" except at the
     trace to pad interface.  This must be .005".  Teardropping the lands
     typically takes care of this so that it doesn't enter into the
     formula, but it must be considered in the design and fab.

     Hope this helps...Andy Slade


______________________________ Reply Separator _________________________________
Subject: Re: [TN] Annular Ring !
Author:  Andy Cameron <[log in to unmask]> at SMTPLink-Hadco
Date:    11/06/98 8:18 PM


I feel the generally accepted industry standard for the determination of PAD
SIZE is the following:

NOMINAL Finished Holes Size + (2 x annular ring requirement) + .010"
(manufacturing tolerance) = Pad size.

Example:  .035 FHS + .004 - .001 = NOMINAL Finished Hole Size = .0365" + (2 x
.002) + .010 = .0505".  I have not read 55110 for a while so just determine
what the annular ring is and plug it in.  Hope it helps.

################################################################
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
################################################################