The guideline is based on design/material and process:
(1) high power chips usually need high conductive adhesive/solder/metallic
bond. The bondline is based on the conductivity of the material and
tolerance of the design (thermal budget). What is your design margin? What
is the material? Conductivity? required pressure upon bonding? (adhesive do
have different thermal condutivity when with pressure and without pressure).
What is the CTE of the material? what is the operating temperature of the
unit? goes above Tg? (CTE is different above Tg==> Thermal conductivity will
be different)
(2) Suggest you start get a Electronic Packaging Handbook for review all
this and take some design course to understand the issue. You may get your
own Guideline.
(3) as for the assembly process, if the design is done correctly, the
assembly process should not be the issue. Are you telling me Dell is not
take DFM into consideration and can not tell you the process? I am sure you
can find someone in the company tell you the complete process. Otherwise,
how could they set up price/yield/cycle time/ profit/ etc.etc.
Good luck.
jk
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Victor Hernandez
>Sent: Wednesday, August 28, 2002 3:11 PM
>To: [log in to unmask]
>Subject: Re: [TN] Die attach/bonding material
>
>
>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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