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Stencil thickness

#34836

Stencil thickness | 9 June, 2005

1. We do have PCB with 0402 component, Micro BGA ( 0.5mm pitch , 0.25 mm pad size ). PCB thickness is 0.8mm. What stencil thickness we should use. PCB size 40 mm X 60 mm 2. We have EKRA E4 , What will be optimum setting for above. Pressure, Scquge speed, snap of, screen cleaning etc. thanks Ajay

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pl

#34839

Stencil thickness | 9 June, 2005

i think tihs one u batter using the printing pallet .The stencil thickness u can use 4 mils thks pl..

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#34840

Stencil thickness | 9 June, 2005

Thanks, 1. Any idea how to go about pallet. because this PCB is single only ( not in multiple ). if you have some drawing / picture pl. send me at ajay_doshi@utlindia.com 2. What are other parameter to set on machine ajay

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PWH

#34860

Stencil thickness | 9 June, 2005

I would suggest 7mm thick "Durostone" as a carrier material. Cut lip/pocket for PCB so it is 0.05" thinner than thickness of PCB. Allow 0.010" gap on all sides of PCB. Machine lip to width between 0.050" and 0.100" to support under perimeter sides of PCB (check for interference with edge parts to determine this). Cut center material completely out as a 0.8 mm thick, small board will support itself (printer is most trouble here). Remember - BGA's will actually pop off of a PCB if the carrier is too tight - so 0.010" gap is a must! An array carrier is most efficient - you can print them one at a time and load them in this carrier. Be sure to profile oven as carrier will heat sink big time, especially parts close to edge. If BGA is near edge, remove Durostone so it doesn't contact near part thus causing unequal heating/cooling of the BGA. Use kapton to tape PCB's in place. If high volume, hopefully PCB supplier can supply as array with rails and carrier won't be needed. Many variable in carrier design - keep it simple. Later!

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KEN

#34868

Stencil thickness | 9 June, 2005

I don't think durastone is ESD safe.

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#34872

Stencil thickness | 10 June, 2005

thanks a lot for info. If you have some photo, pl. send at ajay_doshi@utlindia.com

Photo will help to understand better ajay

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PWH

#34877

Stencil thickness | 10 June, 2005

Durostone CAG762 is the optically sensitive version of ESD safe durostone.

This link shows some good examples of durostone SMT pallets. If you do not have a machine shop, you will have to contract this one out I would say.

http://www.permali.com/pallets/smt.htm

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peter ng

#34920

Stencil thickness | 13 June, 2005

The stencil thickness should be 5.5 mils.The squeeze speed around 20mm/s,print gap 0.15mm,print separation 0.3mm/s.

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Jason Fullerton

#35006

Stencil thickness | 16 June, 2005

If the uBGA has aperatures that are 0.25mm square, you need to use a laser cut foil no thicker than 3.75 mils to get an area ratio of 0.67, which is the minimum rule of thumb - that's too thin!

Electroform would probably work up to 4.5 mils thick.

Better yet, do what I do: overprint your 0.25mm/10 mil pads with aperatures that are 11.8 mils square. Then you can use a 4 mil thick foil and be at 0.74 area ratio.

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