Re: [SI-LIST] : Package Parasitics Modelling

Larry Smith (ldsmith@lisboa.eng.sun.com)
Mon, 29 Mar 1999 11:10:55 -0800 (PST)

> From: gedlund@us.ibm.com
>
> What about a TSSOP package like memory drivers come in? I've found that a
> lumped RLC model still works pretty well for these kinds of packages (i.e.,
> I get good lab correlation) - and the package effects are certainly not
> negligible. I haven't done very extensive power distribution modeling for
> TSSOPs, but my guess is that an RLC matrix would do the job. So I wouldn't
> go so far as to say that lumped RLC models are a thing of the past.

R-L-C lumps are still appropriate for wire bonds, lead frames and peripherally
leaded packages, and they work well. But as solder bumps relaplace wire bonds,
solder balls replace peripheral leads and power plane packages replace
lead frame packages, the dominant parasitics are all distributed. They
are well represented by an impedance and delay. It is posible to represent
them with multiple lumps, but easier with transmission lines.

> I would also argue that an inductance matrix is the appropriate model for
> bond wires in just about any package that uses them. But Larry's right -
> once you get onto the substrate in something like a laminate BGA package
> you need transmission line analysis. Sometimes what you really need is
> coupled transmission line analysis where the cross-section varies as you
> move from the bond pad to the via. This is a difficult structure to
> accurately represent in a package model.

Yes, but that is why we have a mail reflector... and jobs also, come to
think about it.

regards,
Larry Smith
Sun Microsystems

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