For parts opposite a BGA we usually use 0201's, and the pattern and part 
sizes were recommended by the BGA datasheets. 

If you need to use 0402's i would recommend a smaller pad than you stated 
below. We always use 20x20 mil pads, 54 mil toe to toe, and print 16mil 
square.  You will never tombstone with this recipe.

We have never used round for chips, but I have read that it is done, and 
don't homeplate 0402 or 0201, just for larger parts.



Roger Mack  P.Eng. 
Manufacturing Specialist
Parker Hannifin Canada
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB  R3T 1T4 Canada 
direct 204 453 3339 x7373
[log in to unmask]
www.parker.com/ecd







From:   Carl Van Wormer <[log in to unmask]>
To:     <[log in to unmask]>
Date:   2017-03-01 03:22 PM
Subject:        [TN] Reduced size PCB pads for 0402 capacitors on back 
side of BGA
Sent by:        TechNet <[log in to unmask]>



We are designing a new PC board with a bunch of 0402 caps on the back side 
of a 1mm pitch BGA.  The recommended pad size for the caps is rectangular 
(0.63x0.64mm).  The distance between the corners of these pads and the 
pads around the board vias is less than 4 mils (I know I?m mixing metric 
and English units).  We are discussing the possibility of rounding the 
corners to increase the spacing, hoping to reduce the cost of the PC 
boards.  Another possible choice might be octagonal pads.  The extreme 
case of rounding the corners is making circular pads.  I?ve never seen 
octagonal or round pads.

Questions for the group:


  1.  Have you seen round pads used for 0402 caps?
  2.  Will properly sized round pads cause problems with 0402 caps?
  3.   If round pads would work, what is the smallest pad size to 
consider?
  4.  Are there other options that I may be overlooking?

Thanks,
Carl


?????

Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
    21195 NW Evergreen Pkwy Ste 209
    Hillsboro, OR  97124-7167
    503-617-7447x303
    [log in to unmask]<mailto:[log in to unmask]>     
http://cipherengineering.com<http://cipherengineering.com/>

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