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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Dreamsniper

#9835

Step-down stencil Versus Reduced Aperture Design | 2 September, 1999

I'd like to know the advantages and disadvantages between the two.

Thanks and regards,

reply »

Earl Moon

#9836

Re: Step-down stencil Versus Reduced Aperture Design | 2 September, 1999

| I'd like to know the advantages and disadvantages between the two. | | Thanks and regards, | | Both have their place. When using less fine pitch (.025" +) with fine pitch (.020" or less and BGA's) a .007" thick stencil may be used. This would require doing the usual chem mill, as an example, for the big stuff and laser reducing thickness by about .0015". This does require sufficient room around the fine pitch device apertures to allow effective printing with metal squeegee blades and particular paste types.

For all fine pitch, x-fine, and uBGA types, we currently are using thinner foils as in the .005" thickness range without stepping down. Also, at my last contract site, we didn't step down, but reduced apertures to near 1:1, using .006" thick foils, and this worked fine. It would work for most designs here as well, but the folks wanted to take a different course and go thin all over - depending on device types involved. The question is how thin is too thin - and all the results are not yet conclusive.

What I've experienced during the last 3 years, evolving into high I/O count BGA's and CCGA's (1100 + I/O's) and uBGA's, plus extra fine pitch types, it's watever works. However, I really like aperture reduction best after running the experiment while using .006" thick foils as the practical limit. This really works well with frameless foil stencils that maintain very even and constant tension over time.

Earl Moon

reply »

#9837

Re: Step-down stencil Versus Reduced Aperture Design | 2 September, 1999

| | I'd like to know the advantages and disadvantages between the two. | | | | Thanks and regards, | | However, I really like aperture reduction best after running the experiment while using .006" thick foils as the practical limit. This really works well with frameless foil stencils that maintain very even and constant tension over time. | | Earl Moon | That�s what I like best too.

Wolfgang

reply »

PCB Soldering Tools

JTAG Live PCB Debug Software