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Subject:
From:
Brad Saunders <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Brad Saunders <[log in to unmask]>
Date:
Mon, 26 Jul 2010 22:08:13 -0400
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Michael,
Good problem, I'd suggest you get a unanimous vote from your team at work ME, EE, ManE, RelE, and others in the hall.  I have done this a few different ways depending upon application.  In a space -non serviceable- environment we used sequentially plated land to gang PTH directly under component terminal.  Worked fine, expensive but never a problem.  Filled vias in this configuration have a pretty big heritage in reliability.  In another high rel config I used solder masked defined land.  Soldered the part right on a plane that had a opening that defined the land, that worked great and was/is cost effective.
Couple of thoughts.
Brad
  ----- Original Message ----- 
  From: Forrester, Michael (H USA)<mailto:[log in to unmask]> 
  To: [log in to unmask]<mailto:[log in to unmask]> 
  Sent: Tuesday, July 20, 2010 11:34 AM
  Subject: [TN] SMT PAD Current Capability


  I'm a bit confused on how to calculate the current capability of a SMT
  pad.  We have a 2220 size chip bead that has 8A flowing through it.
  Our pad geometry is built per IPC specifications but the manufacturers
  datasheet calls out for a PAD twice the width (part max is 10A). 
  So the question came up, with our current pad geometry (to IPC), what is
  the current capability?  I understand that it is based on the 
  cross sectional area of the copper.  The current density of copper is
  4.02 A/sq-mm.  For a 1 oz copper trace the area is 
  1.4 mils x trace width.  But what do I use for a PAD?  I have an width,
  length, and thickness.  For instance I have a SMT pad that 
  is 1.5mm X 6mm using 1 oz copper with multiple traces coming off of the
  pad.  What is the current carring capability of that pad?   
  Or am I thinking about this wrong?  Thank you.
   
  Best Regards,
   
  Michael Forrester
  Sr. Product Engineer
   
  Siemens Healthcare Diagnostics
  101 Silvermine Rd.
  Brookfield, CT  06804
  PH: (203) 740-6452
   

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