l i a b l eh kC o m p u t i n gL a b o r a t o r y Test Economics for Homogeneous Manycore Systems Lin Huang† and Qiang Xu†‡ †CUhk REliable computing laboratory (CURE) Department of Computer Science & Engineering The Chinese University of Hong Kong ‡CAS-CUHK Shenzhen Institute of Advanced Integration Technology

Observations on Manufacturing Test Cost Manufacturing test is responsible for achieving sufficient high defect coverage As technology advances … Test patterns that target more kinds of errors become essential Accelerated testing methods (e.g., burn-in test) becomes difficult Manufacturing test cost – a great share of production cost In particular, burn-in cost can range from 5-40% of production cost If we are able to relax the coverage requirement, manufacturing cost can be dramatically reduced If we are able to relax the coverage requirement, manufacturing cost can be dramatically reduced

Manycore Processor Era Provides us An Opportunity The integration of a large number of cores on a single silicon die Increasingly popular in the industry yield-driven redundant Traditional yield-driven redundant cores aims to improve the manufacturing yield test cost-driven redundant We propose to introduce a few test cost-driven redundant cores in addition to yield-driven spares for test cost reduction If test cost reduction exceeds the manufacturing cost increment, the total production cost can be reduced If test cost reduction exceeds the manufacturing cost increment, the total production cost can be reduced

Manycore Processor Era Provides us An Opportunity If test cost reduction exceeds the manufacturing cost increment, the total production cost can be reduced If test cost reduction exceeds the manufacturing cost increment, the total production cost can be reduced Consider a 16-core processor To guarantee that all 16 cores work well provided they pass manufacturing test, we need … – Very high defect coverage to identify killer defects – Sufficient burn-in to weed out chips with latent defects Manufacturing test is responsible for 16 out of 20 cores (instead of all 20 cores) to work – Defect coverage requirement can be lowered – Burn-in test can be reduced or eliminated – Manufacturing cost increases

Agenda Background Test Economics with Partial/No Burn-In Test Economics with Partial Manufacturing Test Experimental Results Conclusion

Basics in Yield Modeling Defects on chip – Negative-binomial distribution Defect type Killer defects Latent defects Bathtub curve

Problem 1 [Partial Burn-In] Enable partial/no burn-in test only Given defect coverage requirement, we consider to introduce redundant cores into manycore system that functions if no less than cores are defect-free We fabricate cores on a chip Chips with all cores pass test are sold out Eventually we need to guarantee cores are defect-free at the end of infant morality Determine the number of burn-in driven spares and burn-in time such that … The production cost per sold chip is minimized Product quality constraint is met

The Impact of Partial Burn-In The reliability induced by latent defects follows Weibull distribution with decreasing failure rate Assume that all latent defects reveal themselves after full burn- in time

Product Quality and Chip Test Yield Product quality requirement The probability that a sold chip actually functions at the end of infant mortality should be higher than a threshold – no less than cores on a chip is defect-free at the end of infant mortality – all cores on a chip pass manufacturing test after (partial) burn-in Chip test yield

Product Quality and Chip Test Yield

Define – -out-of- cores are initially defect-free – cores in that set maintain defect-free after burn-in time We obtain

Cost Model Simple yet effective cost model – capture the key impact of introducing burn-in driven redundancy Manufacturing cost – normalize to the case that manufacturing cost of each core for manycore chips without redundancy is 1 unit ATE cost – ATE cost per fabricated core is unit Burn-in cost – normalize the cost of fully burn-in process as unit and assume it is proportional to the burn-in time

Case Study on Partial/No Burn-In Homogeneous manycore system that functions with no less than 32 defect-free cores Product quality requirement is set to 500DPPM

Problem 2 [Partial Burn-In & Relaxed Defect Coverage] Not only enable partial/no burn-in test but also relax the defect coverage for core tests We introduce test cost-driven spares and yield-driven ones We have totally identical cores on chip Chips containing no less than pass- test cores are shipped out Eventually we need to guarantee cores are defect-free at the end of infant morality

Problem 2 [Partial Burn-In & Relaxed Defect Coverage] Determine the number of test cost-driven spares, number of yield-driven spares, defect coverage for core test, and burn-in time such that … The production cost per sold chip is minimized Product quality constraint is met

The Impact of Test Decision Criterion Ideally a prefect manufacturing test is able to reject all bad cores while accept all defect-free ones and In reality … Test escapes False rejects

Product Quality with False Rejects Redefine – no less than cores on a chip is defect-free at the end of infant mortality – no less than cores among all cores on a chip pass manufacturing test after (partial) burn-in Similarly, we have

Product Quality with False Rejects Notations – -out-of- cores are initially defect-free – cores in that set maintain defect-free after burn-in time – among good cores on a chip, pass the test – among bad cores, pass the test We have

Cost Model Total production cost ATE cost depends on defect coverage

Experimental Setup Homogeneous manycore system that functions with no less than 32 defect-free cores (i.e., ) The best, and combination in terms of production cost is determined by exploring solution space System parameters,,,,,, Product quality requirement is set to 500DPPM

Tradeoff between Burn-In Cost and ATE Cost under Product Quality Constraint High defect density Low defect density

Comparison between Traditional and Proposed Strategy 22.28%

Comparison between Traditional and Proposed Strategy 25.26%

Comparison between Traditional and Proposed Strategy

Conclusion We propose to introduce spare cores into manycore system Burn-in test time can be shorten Defect coverage requirement can be relaxed Without sacrificing quality of the shipped products We develop novel analytical models to verify the effectiveness of the proposed strategy

Test Economics for Homogeneous Manycore Systems Thank you for your attention !