That "SPC" chart that runs from 6.5 to 8.5 sounds like an arbitrary set-up.  
Maybe  effort should be put towards finding what the product needs.  Barring 
that, I speculate if there is a viscosity problem, it is too low.  This 
condition allows the paste to (one) slump on itseld, and (two) not withstand the
hydraulic pressure generated by the squeegee.  Watch the temperature 
dependency/effects on viscosity.

Good Luck
Bill Keaton
[log in to unmask]
(507)837-4325 



______________________________ Reply Separator _________________________________
Subject: Re: Stencil design or Solder Paste?
Author:  [log in to unmask] at internet
Date:    4/3/96 8:18 AM


     I would increase the stencil thickness to 7 mils.  With a metal blade, 
     you should not have any "scooping out" of the paste in the aperatures 
     as you would with a polymer blade squeegee.  The paste height I 
     generally get using metal blades and stencils is pretty close to the 
     stencil foil thickness.
     
     
______________________________ Reply Separator _________________________________
Subject: Stencil design or Solder Paste?
Author:  [log in to unmask] at Internet 
Date:    4/3/96 11:37 AM
     
     
Good day,
        We have encountered a low solder paste level in the printing
process.  We are using a Metal squeegee on a Metal Screen to print the 
solder paste onto the PCB before SMT processes.  
        We were wondering whether the solder paste viscosity is too thick;
or there is a Stencil Design fault.  The SPC chart states the solder paste 
thickness should be between 6.5 mil to 8.5 mil.  But we can only achieve 
only up to 6.2 mil of solder paste thickness.  Our stencil is 6.0 mil in 
thickness.
        Can anyone give me the specifications on the design of Metal
Stencils and give suggestions on how to solve the above problems? Thank you.
     
Regards,
Chan Yong Kwee
E-mail:[log in to unmask]
Tel    : (65) 746-6617
Pg     : 9-490-6514