Hi,

  Good question, I look forward to hearing what folks say.

  5 mil might be a little think for something with 0201 parts. A 4 mil thick
stencil might, perhaps, give less variation in release. Even through the
volume is less a more consistent release might buy you a better Cpk. I
think?

Bob Kondner

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rudolph yu
Sent: Monday, December 01, 2008 3:52 PM
To: [log in to unmask]
Subject: [TN] What are the industrial standards for Solder paste printing
limits?

Hi Technetees:
 
One of our customers had asked us to show that our solder paste despoisition
process is capable to acheive Cpk at 1.66 (6 sigma).  We just built a
thousands of pilot boards, and the SPC report I got from the TRI's SPI
machine indicated that the process is able to reach that goal.......however
the software sets the upper limit and lower limits for height, area and
volumn to about +/-50%.  Is this reasonable to have such a high variance in
the printing process? (We use 5 mil stencil with 0201 and fine picthc
aperature).  If I change the limits to +/- 25%, the Cpk will become around
1.33 ( 4 sigma)...should I claims that we can acheive 1.66, and point out
that the  wide tolerence was set by the machine expert, or should I limit
the tolerance spread, and hope that customer will accept lower Cpk.  
 
 
I guess my quesiton is " Is +/- 50% tolerance a resonable limits for paste
printing process?"
 
 
 
BTW the AOI and AXI yield is in the high 98 and low 99 range for this
design. 
 
Thanks
Rudolph 
 

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