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May 1999

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Thu, 13 May 1999 11:59:56 -0600
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See answers to your questions below.

Thanks,

Yuan Li


On Wed, 12 May 1999, Alderete, Michael wrote:

> Li-
>
> 1) Is this a full array of BGA balls, or a perimeter array?
     Full array

> 2) In larger packages, are balls under die, or edges of die?
      Some are under die, a few under edge of die. Have you found that
fatigue life is much lower if balls under the edges of die?

> 3) Is the cross section, and hence construction, of both types known to you?
> If your aren't sure, a cross section on each type will confirm this,
> including die and bond line thickness, (BT) substrate thickness, etc.

  Yes, it is known to me.

> 4) I'm not too familiar with TBGA construction. Could it be that BT
> substrates are much stiffer (in x-y plane) than TBGA? Also, are there heat
> spreaders in these packages?
>
  No heat spreaders. Tape substrate is much thinner (2 mils VS 24 mils for
BT sub.)
>
> -Michael Alderete
>
> Li Yuan wrote...
> ------------------------------
>
> Date:    Wed, 12 May 1999 13:11:40 -0600
> From:    LI YUAN <[log in to unmask]>
> Subject: BGA Solder joint reliability
>
> Dear BGA Reliabilty Experts:
>
> I have done FEM simulations for BGAs and have found some results I cannot
> explain. Hope you can enlighten me on it.
>
> I modeled BT-based BGAs and tape-based BGAs (both cavity up) under 0-100C
> 1 cycle per hour condition. For BT BGAs, with the same die size, the
> larger the package, the better the mean fatigue life. This phenomina may
> be attributed to die/package ratio, the bigger the die/package ratio, the
> worse the fatigue life. However, for tape BGAs (tape substrate is much
> thinner than BT substrate), the result is the opposite. With the same die
> size, the larger the package, the worse the fatigue life.
>
> Can someone explain why the difference between BT and Tape BGAs?
>
> Best regards,
>
>
> Yuan Li
>
> ------------------------------
>

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