If memory serves me right (and it normally does not), there was an article published some years ago that championed oval pads for 0402s. I want to say somewhere around '92 or '93. (0201s were probably new at that time to the masses.) I want to say that it was Motorola(tm) that did the studies, and oval pads and stencil apertures seemed to solve many manufacturing problems for them. I'll have to rummage through my files one day and find it. Can not wait until I get to try my hand at some of that itty-bitty stuff, jealous of those that do... Best Regards, Roger M. Stoops, CID [log in to unmask] TRIMBLE NAVIGATION LIMITED Engineering and Construction Division 5475 Kellenburger Rd. Dayton, OH 45424-1099 USA Telephone: 937 233 8921 800 538 7800 ext. 288 Facsimile: 937 233 7511 http://www.trimble.com -----Original Message----- From: Ahne Oosterhof [mailto:[log in to unmask]] Sent: Friday, April 26, 2002 1:54 PM To: [log in to unmask] Subject: Re: [TN] 0402 stencil aperture design Hi Peter, At Plexus they have published a rather extensive report on the causes of tombstoning. It included some remarks on the incidence of solder balls. Both problem areas are partially caused by pad design on the board and aperture design in stencils. (Some say the most significant factors for tombstoning are pick-and-place accuracy and oven temperature profile.) To minimize tombstoning the report indicates that pad design has a minimal impact when using 0402-s, but for 0201-s you want to stay close to the 'normal' size for pad design. To minimize solder balls it is recommended to change stencil apertures to home plates. My personal preference (and that of some of our customers) is to change the aperture to an oval, which has the effect of reducing excess solder in all four corners of the pads. Sometimes in addition the overall size is reduced by 1 or 2 mil. An additional advantage is that the OVAL is a Gerber shape improving data compactness, data sharing and interpretation reliability and it means that for a single component there are no 'left' and 'right' or 'top' and 'bottom' apertures (or D-codes). Have fun, Ahne. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of peter lee Sent: Friday, April 26, 2002 07:58 To: [log in to unmask] Subject: [TN] 0402 stencil apperture design Has anyone used a "D"-shape 0402 land pattern on their design? The pad dimensions are 18x19mils (semi-circle on the other ends) and 16mil spacing between the 2 pads. What would be the stencil apperture recommendation for the above design? We've used round pads for 0402s and 15% apperture reduction before. Rgds, Peter __________________________________________________ Do You Yahoo!? Yahoo! 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