Page 307 - Semiconductor Manufacturing Handbook

Geng(SMH)_CH19.qxd 04/04/2005 20:00 Page 19.34

INSPECTION, MEASUREMENT, AND TEST

19.34 FINAL MANUFACTURING

due to excessive downtime and/or maintenance costs, or poor yields caused by tester inaccuracy.
There can also be time-to-market drivers that require faster test development and production release.
For business reasons, it may also be desirable to have a dual vendor strategy for testing, which
requires that a second test platform be selected. This approach has a lot of advantages including the
lowered risk of an automatic fallback plan. However, it is difficult to have a close strategic partner-
ship with two vendors. If the SCM model is used, the availability of time on equipment at the test
house must also be considered.
The analysis should include various tradeoffs in test methodologies against capital cost. This
includes such things as engineering characterization versus high-volume production testing, test cov-
erage at wafer probe versus a final package test, and at-speed performance testing versus functional
verification testing with structural (scan and BIST) testing. There should be a target COT based on
the average selling price (ASP) of the device and the overall manufacturing costs. This, along with
other factors, such as throughput, yield, and utilization, will determine the target tester capital cost
required to meet COT goals. For more information on cost-of-test, see Sec. 19.1.
The justification should also include alternatives to purchasing capital equipment. Some alter-
natives include leasing or renting the tester, renting time on a tester at an external engineering test
center (ETC) for test development and characterization, or outsourcing high-volume production to a
subcontract manufacturer. Refer to Sec. 19.1 for more information on the subcontract manufacturing
outsourcing model.
A Purchase Proposal Outline Should Include the Following Segments:

1. Definition of problem statement or gap that currently exists
2. Company philosophy of how to solve the problem citing company core competencies
3. Analysis of the test philosophy chosen and the resources needed
4. Alternatives and their impact on the company and the initial problem statement
5. Request for approval of purchase proposal
6. Post-approval implementation plan including an initial vendor market survey and a decision as to
which vendors to invite to participate
7. “Paper evaluation” to narrow down vendors to a “short-list” of two to four vendors (see Sec. 19.3.4).
Note that the more vendors selected, the more support will be required
a. Benchmark with two to four short-listed vendors including estimated costs for this process
b. Roadmap presentation from vendors that successfully complete the benchmark
c. Selection of primary and secondary vendors
8. Negotiation of contract on final pricing, terms and conditions (T&Cs), and acceptance criteria
9. Placing of a conditional purchase order with the primary vendor for initial system(s) with a pro-
bation period for the vendor to deliver on commitments and meet acceptance criteria
a. Final acceptance and initiation of purchase contract for additional systems, as appropriate
There should be a well-defined, unbiased evaluation process that is clearly documented and well
understood by the evaluation team and the vendors that are invited to participate. The support of
upper management for the evaluation process and their commitment to endorse the decision that is
the outcome of the process is critical.

19.3.4 Building the Evaluation Criteria to Compare Vendors
and Get to a “Short List”

A “paper evaluation” using a list of criteria or “evaluation matrix” is an effective means for com-
paring various vendors and narrowing them down to a “short list.” An evaluation matrix is seldom
used to make the final decision, but rather, to remove unqualified vendors and select the top tier

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.