Browse Prior Art Database

Electro-Optic Sampling for Multi-Layer Ceramic Test

IP.com Disclosure Number: IPCOM000115475D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 108K

Publishing Venue

IBM

Related People

Mahlbacher, JC: AUTHOR [+4]

Abstract

The evolution of Multi-Layer Ceramic (MLC) substrates toward higher levels of integration has resulted in increased I/O requirements, finer signal paths, and denser packing, placing increased emphasis on fast, reliable methods for open/shorttesting of the substrates during their manufacture.In prior art, test techniques have utilized multiple, closely spaced probes arrayed to match the footprint of the electrical contact points on the surface of the substrates to be tested. The probes are then connected to signal cables and switched to isolate opens and shorts. However, conventional test methods have the following shortcomings: 1.

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Electro-Optic Sampling for Multi-Layer Ceramic Test

      The evolution of Multi-Layer Ceramic (MLC) substrates toward
higher levels of integration has resulted in increased I/O
requirements, finer signal paths, and denser packing, placing
increased emphasis on fast, reliable methods for open/shorttesting of
the substrates during their manufacture.In prior art, test techniques
have utilized multiple, closely spaced probes arrayed to match the
footprint of the electrical contact points on the surface of the
substrates to be tested.  The probes are then connected to signal
cables and switched to isolate opens and shorts.  However,
conventional test methods have the following shortcomings:
  1.  Tightly spaced gang probes are costly, can damage and/or
       contaminate the contact points, are only moderately reliable,
and
       limit the types of electrical measurements that can be done
due
       to the impedances they introduce
  2.  The expense of designing probe heads to match each product can
be
       limiting or even prohibitive for low volume products
  3.  Relay switching of probe signal carriers  is  relatively slow
and
       degrades the electrical signal.
  4.  As integration density increases, the physical limits of  probe
       spacing make this approach increasingly less effective.

      Consequently, a method of noncontact testing with high  spatial
resolution  and electrically nonobtrusive measurement capability has
become increasingly desirable.  This need has resulted in a growing
interest in the use of Electro-Optical Sampling (EOS) in high-speed
device testing applications.  With EOS technology, a test signal from
the Device Under Test (DUT) is used as input to an electro-optical
probe, which in turn modulates a sampling laser beam.  The sampling
induces significantly less loading of the circuit than mechanical
probing, is typically noncontact, employs signals in the gigahertz
range, and requires sophisticated sampling and data acquisition
techniques.

      Until now, the application of EOS to substrate testing has not
been widespread because of the relatively low frequency test signals
involved  (typically in the kilohertz-to-megahertz range), and the
relative large feature sizes of substrates.  However, with recent
increases in the levels of substrate integration, the need for more
reliable, nondamaging means of open/short testing has become
critical.

      The adaptation of EOS methodology for MLC testing disclosed
herein provides nonconta...