Browse Prior Art Database

Quick Tester Calibration Using Standard Chips as Multiplexers

IP.com Disclosure Number: IPCOM000111024D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 79K

Publishing Venue

IBM

Related People

Hivert, C: AUTHOR [+2]

Abstract

On present high speed manufacturing testers, signal transmission between tester and chip is achieved by cables and a space transformer. The main cause for inaccuracy is the poor impedance control in the space transformer. This poor impedance control limits tester autocalibration accuracy at 300 ps. In order to to reduce the impact of this inaccuracy, testers used on the same product, are adjusted together using reference chips. Worst case accesses are measured for all data out on a reference tester. Overall access of other testers is adjusted so that the worst case access of the slowest data out matches the one measured on the reference tester. This method is not accurate because the slowest data out and the slowest cycle is not the same for all testers.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Quick Tester Calibration Using Standard Chips as Multiplexers

      On present high speed manufacturing testers, signal
transmission between tester and chip is achieved by cables and a
space transformer.  The main cause for inaccuracy is the poor
impedance control in the space transformer.  This poor impedance
control limits tester autocalibration accuracy at 300 ps.  In order
to to reduce the impact of this inaccuracy, testers used on the same
product, are adjusted together using reference chips.  Worst case
accesses are measured for all data out on a reference tester.
Overall access of other testers is adjusted so that the worst case
access of the slowest data out matches the one measured on the
reference tester.  This method is not accurate because the slowest
data out and the slowest cycle is not the same for all testers.  For
this reason the result of the calibration depends upon the reference
chip used.

A solution to get better accuracy is to calibrate every tester as
follow:

o   Disconnect tester from transmission cables and calibrate it using
    a cable having known transmission delay.  This cable is used to
    connect, one tester driver to all receivers successively, and
    then, one receiver to all drivers successively.

o   Measure by Time Domain Reflectometry the delays of transmission
    cables and space transformer.

This method can give up to 30 ps accuracy by using state of the art
sampling oscilloscopes.  However it is not suitable for manufacturing
because it takes 1 or 2 days.  Such calibration time is not
compatible with manufacturing requirements.

      The object of this disclosure is to use standard chips as
multiplexers, to perform the connection between one tester driver and
all receivers, and between one receiver and all drivers.

      Access times of standard chips are first measured using
sampling oscilloscope.  Good enough accuracy in standard chip
measurement can be achieved using following features:

o   Use cables with tight controlled impedance: 50 +/- .3 Ohm.

o   Pick up scope signal on chip input by dividing the signal coming
    from tester in two e...