Andy,
Michael gave a good answer, I had two PBGA from the same vendor, with same
enviroment exposition but the small 324 pins PBGA came with popcorning
during reflow and the bigger 492 pins no problem. I asked Intel why that
happened only with the small one ( Intel forum ) but no answer yet. The rule
seems to be item 4 below in michael e-mail, but the component suppliers give
a generic exposure time to safelly cover many differente sizes.
Intel has a Packaging Databook available for download and chapter 8 is "
Moisture Sensitivity / Desiccant Packaging / Handling of PSMCs " that could
help you also.
http://developer.intel.com/design/packtech/packbook.htm
Thanks
> -----Original Message-----
> From: Alderete, Michael [SMTP:[log in to unmask]]
> Sent: 23 de Abril de 1999 16:14
> To: [log in to unmask]
> Subject: re: Popcorning <IPC TN>
>
> Andy-
>
> I looked through a few recent, and older, papers this morning, and learned
> a few things:
>
> 1) I believe the answer to your question depends, roughly, on package
> type/style (size?).
> What plastic packages are you concerned about? PQFP? CSP? TSOP? PBGA?
>
> 2) Much has been written about PBGAS, especially by the people at
> Motorola. Some papers I have listed in a "references" file include:
>
> a) Diffusion Model to Derate Moisture Sensitive Surface Mount ICs for
> Factory Use Conditions ... "derates JESSD22-A112 and IPC-SM-786A moisture
> levels for factory conditions other than 30°C/60%RH...
> IEEE Trans., CPMT-C, April 1996, p110
> (10) 12 ref
> Shook, Richard L., Conrad, Timothy R., Sastry, V. Srirama, & Steele, David
> B. [all AT&T Bell Labs]
>
> b) Moisture Uptake and Release by Plastic Mold Compounds- Its Relationship
> to System Life and Failure Mode
> IRPS Proc., April 1980, p293
> (8) 2 ref
> Dycus, Dale W. [Mostek Corp.]
>
> c) Effect of Mold Compound Components on Moisture-induced Degradation of
> Gold-Aluminum Bonds in Epoxy-encapsulated Devices
> IRPS Proc., April 1990, p244
> (7) 11 ref
> Gallo, Anthony A. [Dexter Elec. Matl. Div.]
>
> d) The relationship between moisture resistance and epoxy molding
> compounds in integrated circuits
> J. Electronic Matl., 1984, C- p231
> (20) ref.
> O. Nakagawa, I. Sasaki, H. Hamamura, & T. Banjo [Mitsubishi Elec Corp]
>
> e) The PBGA: A systematic study of moisture resistance [Best Paper]
> Proc. IEPS Conf. 9/94, September 1994, C-p588
> (15)
> Hawkins, George, Ganesan, G., Lewis, G., & Berg, H. [all Motorola]
>
>
>
> 3) Guessing that you have a PBGA package, I'd highly recommend you see
> paper 2e) above. There's a wealth of information in this paper regarding
> the materials and interfaces that may be the source of popcorn
> susceptibility. It's amazing that Motorola sorted all this out in 1994!
>
> The IEPS paper says...
>
> "...Since failure initiates in the die attach zone, it is the moisture
> entering the die attach that is most critical." [page 590]
>
> Figure 2 of the paper is a plot which shows, roughly, popcorn
> susceptibility when % weight gain <due to moisture> is greater than 0.23%
> @ 74% RH, and 0.17% @ 53% RH
>
> Figure 7 of the paper states that for a particular PBGA studied, the
> "critical moisture concentration in die bond = 2.475E-02 grams/cubic cm"
>
>
> 4) It appears there is no simple answer to your question, based on my
> skimming through paper 2e). You could probably say that for a given type
> of PBGA,
>
> x by Y mm in size, with xxx balls, full array, "average" die size = xx x
> yy mm, using "typical" overmold epoxy compound X, die attach material Y
> (Ag filled epoxy), with PWB substrate [BT material, XYX soldermask over
> Au/Ni/Cu die attach pad, pad metal exposed only minimally to die attach
> material.],
>
> popcorn susceptibility for your reflow process occurs ABOVE (0.2??) %
> weight gain due to moisture absorption.
>
>
>
> BOTTOM LINE: This probably yields a decent rule of thumb limit for
> acceptable moisture absorption, which can be calibrated to ambient air
> exposure (RH= yyy%) for xxx hours in your particular assembly floor.
>
> Hope this starts to help.
>
> Michael Alderete
>
>
>
> Andy Mackie wrote...
> ------------------------------
>
> Date: Thu, 22 Apr 1999 15:33:48 -0400
> From: Andy Mackie <[log in to unmask]>
> Subject: Popcorning
>
> Hey, Techdudes: Quick one for you....
>
> How high does the (water vapor) pressure in a package have to get, in
> order
> to see popcorning occurring? I know it will depend on the package etc, but
> pitcher's mound (i.e. "closer than ballpark") figures would be great.
>
> Thanks!
>
> Andy
>
> ------------------------------
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