Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Stencil thickness

Views: 1330

#59987

Stencil thickness | 25 September, 2009

0.5mm pitch QFP's are typically mixed with large components on all of my boards. I usually use a 6 mil stencil with a minimum aperture width of 10 mils. Normal aperture size is 10 x 50 which causes shorts about 20% of the time. A recent purchase of a used LSM height measurement system shows paste height of 7.3 to 8.2 mils. To compensate for the additional paste height, I could go to a step stencil for the QFP, reduce the aperture to 10 x 40 or go to a 5 mil stencil and take a lot of time increasing the paste on the rest of the parts. What are you doing to solve this problem.

reply »

#59993

Stencil thickness | 27 September, 2009

The same issue i faced 2 yrs before , i sugest

1. Use stencil of 4 mils ( Take care of Aspect Ratio and Area Ratio ).

2. Use Solder Paste of Type 4.5 and Viscosity in between 1100 to 1300. ( Try Solder Paste of Cookson or Alpha metals : OM338 T45-LF and OM6106 leaded )

This defibately helps u.

reply »

#60006

Stencil thickness | 28 September, 2009

Search the fine SMTnet Archives to find threads like: http://www.smtnet.com/Forums/Index.cfm?CFApp=1&Message_ID=39954

reply »

PCB Soldering Tools

Reflow Oven