John:

We do a lot of fine pitch testing for flex circuits, MCM's, Ceramic, etc., to about 0.008".  We
use a spring probe that's about 0.735" in length and has a plunger with a diameter of 0.006". We
couldn't find them on the market so we have them made for us.

After you calculate pointing accuracy of the probe itself, you must consider other error factors
as well.  The concentricity of the probe to the receptacle, and the receptacle to mounting hole
will impact probing accuracy.

Regards,
John Alesi

[log in to unmask] wrote:

>      All,
>
>      I luckely found some calculations for determining pin deflection, hole
>      diameter, pin length, hold (yes HOLD) diameter, etc. for Testing Fine
>      pitch devices (.010", .012") and BGAs.
>
>      Is anyone familiar with these formulas?
>
>      HSmin = SD + PT (tanO)
>
>      0 = sin-1 (Pd/Pl)
>
>      HSmin = (SD + PT)(PD/PL)
>
>      LEGEND
>
>      HSmin - min hold diameter
>      SD - shaft diameter
>      PT - plating thickness
>      0 - angle of deflection
>      PD - pin deflection
>      PL - pin length
>
>      Can I use these formulas to determine if testability is feasible, for
>      a very high dense assembly {4 - 600 I/O BGAs with 30 - .020" pitch
>      devices (160-pin nominal) in a 9 x 7 form factor}.  I feel I am
>      missing several pieces to the overall formula picture.  Can someone
>      advise where I can obtain the rest of the equation.
>
>      John Gulley
>
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