Electronics Forum | Tue Aug 03 08:38:42 EDT 2004 | davef
Conductive epoxy is usually specified as less than 6:1 aspect ratio fill capable, while non-conductives are 10 to 14:1 (depends on which brand and who you ask).
Electronics Forum | Wed Sep 08 07:06:36 EDT 2004 | peter016
Hi Rob, Thanks for the reply. Our boards are 4 ~ 6 ups and mostly double sided. The ratio between chips and IC/Odd shape varied from products to products. So, line balancing between chipmounter and GSM is tough to do. Some boards are mirror image to
Electronics Forum | Fri Sep 17 14:30:06 EDT 2004 | russ
You are right, playing with apertures is how to ensure release. Making a stencil thinner or thicker is "playing with apertures" It all relates to aspect and area ratio calculations and what you need to do based upon the numbers you get. Russ
Electronics Forum | Tue Feb 08 10:33:26 EST 2005 | Dougs
have you had any reduction in aperture size though, we generally use a 6 mil stencil thickness with a 10% aperture size reduction for chip components and leaded components ( SOIC - QFP ) and a 1:1 ratio for BGA components without any problems.
Electronics Forum | Fri Mar 18 14:32:43 EST 2005 | pmd
Im not fimiluar with SIEMENS F5 but I believe that lead length devations translate to coplnary devations. As a lead gets bent inward or outward the coplnary changes. I dont know what the ratio is but you may be able to set tolorances for lead length
Electronics Forum | Thu Jul 14 16:08:07 EDT 2005 | russ
Stencil thickness is related to PCB design and is not related to paste type. If you release with a 8 mil stencil then use an 8 mil stencil. Of course there are pastes that release bteer than other and what not but use area and aspect ratios to dete
Electronics Forum | Wed Aug 31 10:50:50 EDT 2005 | aj
Grant, We run the exact same process as you described. 5 thou stencil, 1:1 ratio aj
Electronics Forum | Tue Sep 20 15:37:24 EDT 2005 | intermin
Well, at that value point, I'd go with the hourly ( unburdoned ) high-skill rework/repair rate up to 50%-60% of the board value. If this is part of an integrated system ( in-house assembly ) repair to value ratio could go even higher.
Electronics Forum | Thu Dec 08 09:47:46 EST 2005 | slthomas
I'm with Grant on the .005" foil thickness. The key is to keep your aspect ratio (aperture width/foil thickness) over 1.5, laser cut, and I like trapezoidal aps. too.
Electronics Forum | Tue Jan 31 13:55:56 EST 2006 | samir
Anyone know what the general rules / requirements are for micro-BGA's and CSP's as to when capillary underfill is required? (ie size of bump/ball, package thickness, PCB/CSP thickness ratios, etc).
