Leo,
Thank you very much for your contribution to my BCC package ball bond
question. My concern was the voids at the inner portion of the ball
bond. Are there any related articles to this package style that I can
read for reference purposes.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leo Higgins
Sent: Sunday, March 18, 2007 5:18 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
The photos posted by Steve show this to be a cross-section of a BCC
package assembled on a board. BCC packages are made by etching pits in
a Cu carrier sheet in locations of the BCC package surface mount pads.
The surface of the etched pits are then plated with a series of thin
metal layers, starting with a layer for surface mount solder assembly,
and terminating with a layer suitable for Au wire bonding. The die are
assembled on the Cu carrier sheet and wire bonded to the plated surfaces
in the pits. The fact that their is a ball bond made to the pit surface
indicated that this is a case of a 'reverse bond', or 'bump stitch on
ball', type of bond. When this is done a ball bond is made on the die
pad, and the wire is broken off just about the ball. Then the ball bond
is made in the pit, and the stitch bond is made to the ball bond
previously made on the die pad, allowing very low loop wire bonds,
allowing very thin packages. After die attach and wire bonding, the
surface of the Cu carrier is transfer molded, and you can see the fused
silica filler particles in the epoxy matrix of the mold compound in the
photos. The Cu carrier sheet is then etched away, and the plating in
the etched pits acts as an etch-stop. Then the individual packages are
saw-singulated. The package has protruding bumps on the bottom side
that are clad with the multilayer metal stack previously plated into the
pits in the etched carrier. My company makes a package, called TAPP,
with planar bottom side pads and exposed die attach pad using a related
process technology. The roughness of the metal to which the ball bond
is made appears rougher that what I would expect, and is rougher than
the surface of the metal stack to which we bond Au wires in a similar
construction. Since this ball bond is being made to a very thin noble
metal surface, it is likely that no IMC phase is formed between the ball
and the pad metal stack. The bond may be reliable, but the roughness
appears to be allowing voids to remain in the interface of the ball bond
and the pad surface, and this is not desirable.
Best regards,
Leo
Leo M. Higgins III, Ph.D.
Sr. Vice President, Engg and Technology
ASAT, Inc.
13809 Research Blvd., Suite 635
Austin, Texas 78750
office phone 512-249-4758
mobile 512-423-2002
[log in to unmask]
www.asat.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Inge
Sent: Friday, March 16, 2007 2:02 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Both, in fact. Yep, the plater cooperates understandingly. Nota bene: if
you
bond on nailheads or any similar pins, you need keep an eye on the U/S
frequency. The pins can swing with the horn, and that can cause poor
adhesion.
So, Trikeman, you begin to feel altitude excitement. I understand. I've
seen
young bird's whole body vibrate and suddenly they can't resist any
longer,
but jump from the bird nest and swing up in the sky, anxiously but
triumphing. Go, Trikeman, fly with the eagles! But don't drop things on
my
head. (I don't know how much bird you become up there)
Inge
----- Original Message -----
From: "Creswick, Steven" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 16, 2007 11:12 AM
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Okay Ingemar,
Are you putting the ball on the [nail head?] pin, or the wedge? I bet
your plating/plater has a lot to do with your success :-)
Sometimes you crack me up!
I need the weather to calm down so I can go flying. Starting to grow
roots have been on the ground so long. Finally loosing enough snow that
I might be able to get out on the field.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, March 15, 2007 5:18 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Copper Cup...when is that?
Sorry, I know you are not to play with until on Friday.
Even if the surface you are looking at may seem rough in a macro-looking
perspective, the micro ditto may serve well for the ball or wedge.
Hence, we
do bonding on rough glass feed-true pins, which are absolutely not
thought
for bonding, but it works fine. Try! And do pull test!
Inge
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>; <[log in to unmask]>
Sent: Thursday, March 15, 2007 7:48 PM
Subject: RE: [TN] Gold Ball Bond attaching surface roughness
The application I am referring to is a device where the ball bond, BCC,
is placed on a copper cup which also serves as the solder fillet to the
PWB pad.
This cup is really rough exhibiting tooth like structure similar to
those of the vendor treated side on copper foil.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, March 15, 2007 12:23 PM
To: [log in to unmask]
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Agree with Trikeman, the semi process is a epitaxial process using
"refractory" metal, and the asperity is not measureable on normal
tallysurfers, i.e. <0.1 um. Only situation may be with semi chips with
plated bond pads, but then we talk gold. And these have never caused us
any
problems either. You needn't bother. /Inge
----- Original Message -----
From: "Creswick, Steven" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, March 15, 2007 1:36 PM
Subject: Re: [TN] Gold Ball Bond attaching surface roughness
Victor,
Sorry, don't have a number to give you. We do it all day long ... and
the IC mfr's know how to make the bond pads....
Typically smoother is better, but if one were to look at the plating on
a lead frame at high enough magnification, it is certainly not smooth
either.
Possibly someone has some form of spec on the surface finish of a bond
pad. All that I am aware of is pad thickness.
If no one has a surface finish number, I might be able to run some next
week.
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor G. Hernandez
Sent: Thursday, March 15, 2007 8:25 AM
To: [log in to unmask]
Subject: [TN] Gold Ball Bond attaching surface roughness
Fellow TechNetters:
Typically I have observed ball bond attached the alunium window of a
chip, and copper lead frame. Are there any criteria for the roughness
of this surface for establishing a good intermetallic formation?
Victor,
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