FreeLists / si-list / [SI-LIST] Re: soldering plastic balls

["Lars Juul" <write2larsj@xxxxxxxxx>]

Hi Steve,
I'm surprised to hear that the primary objective with the plastic core balls
is to equalize the resistance over frequency, as Sekisui write on their
product page:

(http://www.sekisui-fc.com/eng/html/jissou/product/jipr_02.html)
...
Micropearl SOL is a solder plated true sphere with a plastic core and was
designed for mounting chips to circuit board. Unlike conventional solder
balls which often cracks under the heat cycle test,
...

They go on to show graphs with how much longer these solderjoints will hold
in temp cycle tests comparison to SnAg alloys, which I feel is very relevant
in these RoHS times.

However, it's true that at high frequencies the current flows on the edge of
the conductor (in closest possible proximity to your return current), and
that the lack of conductor diameter will lead to increased resistance closer
to low frequencies, but I doubt that it will act as a good loss equalizer (I
might be wrong, I guess)


2007/6/5, steve weir <weirsi@xxxxxxxxxx>:
>
> Lars, the idea of the plastic balls is that they have only  a thin outer
> conducting layer and therefore the resistance remains much more uniform
> and therefore equalizing loss across a broad frequency range.
>
> Steve.
> Lars Juul wrote:
> > Hi David,
> > I would call up your packaging vendor and ask them to make a test build
> with
> > ball samples from Sekisui on existing 10 Gbps BGAs, provided the ball
> attach
> > tool is suitable for this. This is usually the stumbling block, as this
> is
> > very expensive in NRE.
> >
> > Alternatively, it's worth exploring if you make a manual ball attach
> > (possible if the packages are for small form factor 10Gbps CDRs, for
> > instance) by printing solder paste on the package lands first, and then
> > manually place the balls  on the paste by a trained person with a steady
> > hand. I assure you, crazier things have been made.
> >
> > On the other hand, my only concern with this kind of balls would be the
> > suitability for them in the power supply, as I imagine the current
> carrying
> > capabilities are somewhat limited if you have a plastc core on the
> inside.
> > (I don't think it's possible to attach solid solder and plastic balls on
> > specific lands on the package in a high volume setup, yet)
> >
> > PS: you're asking whether they work at 10GHz, which is a single
> frequency
> > point, I think it's feasible to use plastic core balls for a narrowband
> > application, but if it's broadband from 0 to 10e9 Hz you're driving at,
> I'd
> > say, try it out in practise first to see if it flies, then make a full
> wave
> > or macromodel of package afterwards to feed the chip I/O designers.
> >
> > Have fun.
> >
> > Best regards,
> > Lars
> >
> > 2007/6/5, david stern <dan1_st@xxxxxxxxx>:
> >
> >> hello all
> >>
> >>   I was looking for bga soldering balls  technology for an
> >> application working at 5GHz to 10GHZ and  and found
> >> soldering plastic balls from SEKISUI. Did somebody work with them at
> >> 10Ghz?
> >>
> >>   Thanks
> >>
> >>   David
> >>
> >>
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