Hi Alejandro,
 
are you sure that your design fits the component ?
With similar pitch we a ballsize from 0,60mm to 0,90mm and nominal size
0,75mm for the balls.
Our design looks like:
0,60mm pad diameter (24mil)
0,76mm soldermask opening (30mil)
0,33mm pad-to-via distance (this is measured)
0.64mm via size for 0,3mm finished via diameter (25mil)
there´s no soldermask opening for the via´s defined
 
This may not be the optimum but has caused no trouble yet using 150µm (6mil)
stencil and an aperture reduction of 15%.
 
You might check your design so that it´s not at the limit or your paste
printing.
For the part itself, if it´s in the specified limits, you can´t do anything
(accept taking that into account during design )
 
hope this helps
 
Wolfgang
 
 
 -----Ursprüngliche Nachricht-----
Von: Becerra Alejandro [mailto:[log in to unmask]]
Gesendet am: Montag, 27. August 2001 23:16
An: [log in to unmask]
Betreff: [TN] Solder Shorts in PBGA


Hello to All, 
We have had solder short in a PBGA with a pitch of 1.27 mm. 
The short is between one solder ball and an adjacent via pad. 
The problem is only shown in specific date codes of the component. 
We measured the solder balls and there are differences between the diameter
of the solder balls: 
The average diameter in the "good" date codes is 0.58 mm and in the "bad"
date code is 0.63mm. 
The specs. states that the diameter could be between 0.50 and 0.70 mm; then
both date codes are within specs. 
We also found that the soldermask over the via pads is not well centered
causing that solderable surface in some 
via pads be closer to the solder balls. 
Is it possible that the solder short could be caused by the combination of
these two issues? 
Thanks in advance. 



Alejandro Becerra

Quality Assurance

Phone (915) 841-8439, Fax (915) 841-8401

[log in to unmask]

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