BSOB is also called "stand-off stitch". Not what we have here.
What we have here is how the designer solved a problem where two connections had to be done to a single die pad. I've seen that done with a multi-stitch ball bond (much more common with wedge bonds), but very few bonders support that profile. So this designer elected to simply stack two balls.
The weak point is the weld between the ball on top and the wire/ball it's being stacked on. While it is frequently dismissed as "it's a gold to gold bond, so anything goes" I have found failures. The problems with making them reliable are:
1. Ball bonders are nearly always used in "thermosonic" mode, with an emphasis on the "sonic". Most of the weld energy comes from the ultrasonic scrubbing. But with the fully annealed soft gold ball, it is hard to get reliable scrub--even without the fact that the surface being welded to is so irregular.
2. There is no simple way to qualify such a bond. Ball bonds are typically qualified by shear test because the weld area is much larger than the wire area (a pull test should always fail in the wire). But this stacked structure doesn't lend itself to shear testing. So the tech has no way of setting up the bonder to get statistically relevant results without doing thousands of bonds.
Despite these two misgivings, everyone who bonds complex assemblies ends up doing this occasionally and they seem to have a reasonable service life. And they are allowed as repairs for US mil spec parts (not sure about space qual).
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Wednesday, October 27, 2010 10:23 AM
To: [log in to unmask]
Subject: Re: [TN] Unusual Au ball bond
Try google wirebond BSOB (not a bad word).
--------------------------
Sent using BlackBerry
----- Original Message -----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Wednesday, October 27, 2010 10:13 AM
To: [log in to unmask] <[log in to unmask]>
Subject: Re: [TN] Unusual Au ball bond
Hi Vict..I mean, "X",
Here's your pictures:
http://stevezeva.homestead.com/X-sec-1c.JPG
http://stevezeva.homestead.com/X-sec-1g.JPG
It looks like they wanted to be double sure that it worked ;^)
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Wednesday, October 27, 2010 9:01 AM
To: [log in to unmask]
Subject: [TN] Unusual Au ball bond
Fellow TechNetters:
Has anyone seen a ball bond as suck and is it reliable? Photo was sent
to Steve Gregory.
"X"
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