The plexus report is published in '98 and is still pretty up-to-date, but it doesn't have much info about stencil apertures (but it's still interesting).
The report has disappeared from the plexus website, but you can still download it at http://www.smtinfo.net/docs/tombstoning.pdf
B.T.W. I'd say that even now 0201's are new to the masses, don't you think so Roger ?
Daan Terstegge
http://www.smtinfo.net
----- Original Message -----
From: Roger Stoops
To: [log in to unmask]
Sent: Friday, April 26, 2002 10:10 PM
Subject: Re: [TN] 0402 stencil apperture design
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
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