The solder in the corners may also be the source for solder
balls. Molten solder wants to take the shape of a sphere. The corners
pull the solder away from the sphere shape and with vibration some of
the solder may actually separate and fall out. This may happen specially
when there is extra solder on a pad.
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of DUTTON Phil
Sent: Tuesday, October 24, 2006 1:58 AM
To: [log in to unmask]
Subject: Re: [TN] Round Pads for Discrete SMD's
Hello Richard,
I've been doing this for some time now for 0402 SMDs for all the reasons
that you mention.
(especially under 1mm pitch BGAs.)
The extra solder out in the corners of a square pad is significant with
these small devices and can contribute to tombstoning and drawbridging.
My 0402 is 2 x 0.7mm round pads at 1.1mm centres.
regards,
Phil.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Smith, Richard
Sent: Monday, 23 October 2006 11:22 PM
To: [log in to unmask]
Subject: [TN] Round Pads for Discrete SMD's
Folks,
Many moons ago (circa1985) I attended a seminar on SMD land pattern
design where the speaker said (as he gazed into his crystal ball) that
round pads could potentially become the pad of choice for 2 pin SMD's.
If I remember right he said that some of the benefits of round pads were
better solderability, less tombstoning and more room to route traces. He
added that this was a hot subject in Japan at the time.
Since then I havn't seen any boards with round pads for discrete SMD's
which makes me wonder. Is anybody using round pads for SMD devices? Has
anybody ever heard of doing this and know any reasons why it didn't
work?
The reason this came up is that round pads would be beneficial when
placing bypass caps and terminators between the via fan-out pattern of a
BGA.
Thanks Much!
Regards,
Rick
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