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August 2002

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Subject:
From:
Victor Hernandez <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 28 Aug 2002 14:10:32 -0500
Content-Type:
text/plain
Parts/Attachments:
text/plain (167 lines)
Steven, and other TechNetters:

   The die size is .156" x.098" (156x98 mils).   I known NOTHING of the
Assembly Process and Equipment.   I only have results from a cross section
I conducted.   Is this observation worth perusing as an Assembly Process
Capability Issue and/or Concern stand point.   In a previous life with
big blue this was worth high lighting to the vendor.

   I would rather arm myself with industry requirements/guidelines before
asking the vendor what their process should yield.

    I don't want the FOX guarding the HEN house.

victor,


-----Original Message-----
From: Creswick, Steven [mailto:[log in to unmask]]
Sent: Wednesday, August 28, 2002 11:48 AM
To: [log in to unmask]
Subject: Re: [TN] Die attach/bonding material


Victor,

I ditto the comments made by Bill (below).

With respect to polymeric attachments - the cured bondline thickness
(adhesive thickness beneath the device) is somewhat determined by device
size, equipment set-up, and material requirements.

With most 'normal' die attach adhesives, you will get something like 0.5-1.5
mils (0.0005-0.0015") of bondline thickness for die in the size range of
8-50 mils per side.  Larger die usually result in greater bondline
thicknesses - partially by design (to better absorb stresses).  For a device
0.250" square, I would expect a bondline thickness of around 2-2.5 mils
(unless, by design, or material requirement, I was seeking something
different).  Some low-stress die attach materials actually seek bond lines
in excess of 3 mils.  Check with your polymer supplier for their specific
process recommendations

Your placement equipment has a role in the process too.  If you go and try
to place a 10 mil square device with a whopping 300-400 grams of placement
force, you can count on your bondline thickness being on the low side (and
or a crushed device or pick up tool).  Now then, if you were to place it
with a more reasonable 15-30 grams, you may find my numbers to be more
realistic.  Everthing is relative to your set-up and materials choices - no
one can second guess from a distance.

With respect to fillets - If you want to maximize heat transfer out of the
chip, keep your fillets up.  How high??  Personnally, if you are 50% up the
side of the chip you are high enough!  Why risk buggering up the wire
bonding process with adhesive resins which may wick up the side and over the
top of the chip.  If you do not have the realestate to create larger fillets
- your design is your limiting factor.  Generally, fillets improve die shear
strength (by effectively increasing the contact area).  If you have a
'normal' 18-20 mil thick device, and you have fillets 5-8 mils up the sides
- that should look nice!  IF you had a 4 mil thick LED and you have fillets
that tall, you just rendered the chip non-usable!!  THere goes "its all
relative" thing again.

With respect to skew - How much skew can your wire bonder accept before the
pattern recognition systems fails to capture the image?  5°?  10°?  If you
have wires crossing where they should not be - you have too much skew,
otherwise "too much" is somewhat established by your design.

Hope this helps a little bit (more/too)

Steve Creswick - Gentex Corporation




-----Original Message-----
From: Bill Christoffel [mailto:[log in to unmask]]
Sent: Wednesday, August 28, 2002 8:34 AM
To: [log in to unmask]
Subject: Re: [TN] Die attach/bonding material


IMHO, some of the best information regarding die attach (alloy or polymeric)
can be found in good old MIL-STD 883  (Method 2017 section 3.1.2, Element
Attach)  Note: a lot depends on the specific type of component due to
defining active circuit area.  If you have specifics feel free, this has
been my area for over 20 years.

Bill C.
Advanced Manufacturing Engineer
NorLux Corp.

-----Original Message-----
From: Victor Hernandez [mailto:[log in to unmask]]
Sent: Tuesday, August 27, 2002 1:22 PM
To: [log in to unmask]
Subject: Re: [TN] Die attach/bonding material
Importance: High


Mr. MoonMan & Fellow TechNetters

   Can you please direct me to some literature/Requirement for die
attach/bonding material thickness.   Min and Max thickness.  How far
up the thickness of the die can the bonding material cover.

  Along that same line what is the skew aloud.

victor,

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