An Improved VLSI Test Economics Analysis System - Laboratory for ...

ogy incorporating structural, behavioral, qualitative and quantitative aspects of known DFTtechniques.The successor of TDES is TIGER (Testability Insertion Guidance ExpeRt [2]), whichis now an industrial tool. It handles gate level descriptions, and uses a more sophisticatedpartitioning process than TDES. It uses a similar weighting system to evaluate embedding,mainly in terms of area overhead, estimated test pattern generation (TPG) eort, and estimatedtest time.Brendan Davis proposed EVALUATE [3] which is a decision support tool mainly forthe manufacturing test strategy part of the overall test strategy in 1994. It also includesthe design to test strategy and the eld-service strategy. Since EVALUATE produces anindication of the likely number of defects that will `escape' to the eld for each dierentstrategy analyzed, it eectively provides a measure of the eld-service workload also.1995, Dislis et al. proposed test strategy planners called ECOtest and ECOvbs [4]. TheECOvbs applied the same principles of economics to board designs as ECOtest did to ASICdesigns. It fully calculated the economic and technical eects of test method and also oerssome design optimization and a range of dierent test strategy planning algorithms.All of above papers estimate test cost of well-designed circuits. However, many DFTmethods must be applied before detailed design. Models should not use the parameterswhich is dicult to obtain or estimate in the oor-planning stage. Kim [5] proposed a testcost prediction model which estimates the cost of IC testing in a manufacturing environment.This model predicts chip testing cost and quality of test using a set of circuit manufacturingparameters. Those parameters are available at the early stage of the design cycle. But, theirmodel did not consider the condition of DFT.In [6], another cost model called CMU Test Cost model was proposed. Then, this modelwas used with a range of parameters representing typical industrial conditions to nd athreshold volume. This volume indicates if we get benet from DFT. They found thatcost and benet of DFT is strongly aected by the volume. Similar result was obtained byWei [7]. This paper just found the relation among DFT related parameters, cost and volume.However, they did not describe how DFT methodologies aects these parameters.In our research group, the "Evaluation System for TEst Engineering methodologies (ES-4