Stress Screening Chamber Selection and Implementation

Publisher: Accolade Engineering Solutions

Format: PDF
Date: 2008-11-26

View all
Accolade Engineering Solutions
White Papers

Overview:
This paper serves as a tutorial for an engineer implementing a new production stress screening program, and provides guidelines for equipment selection based on a given set of stress screen performance requirements, information to properly implement the stress screening system, and methods to calculate best case chamber performance. It begins with the study of screening requirements and facility constraints documented during the Highly Accelerated Life Test (HALT), followed by chamber design considerations for selection. The different forms of supply liquid nitrogen required by the stress screening system to perform the primary cooling function or to provide a boost capability to assist a mechanically refrigerated system are discussed, followed by chamber performance calculation. A comparison is drawn on potential chamber implementations showing capability and approximate cost of usage. Finally, it concludes that the HALT process provides a set of target stress screening parameters for the production level stress screen.

TABLE OF CONTENTS
1.	Introduction	2
2.	References	2
3.	Background	3
4.	Chamber Design Considerations for Selection	4
5.	LN2 Facilities	11
6.	Chamber Performance Calculation	14
7.	Chamber Use Model Comparisons	17
8.	Summary and Conclusion	22
9.	Appendix A	23
10.	Appendix B	24
11.	Appendix C	25
12.	Figures	4
12.1.	Product Response for the Low Airflow Case	4
12.2.	Product Response for the Proper Airflow Case	5
12.3.	Single Zone Chamber Layout	6
12.4.	Two Zone Air-to-Air Chamber	6
12.5.	Cascade Refrigeration Performance for Various Compressor Sizes	7
12.6.	LN2 Performance for Various Screening Temperatures	8
12.7.	Heating Performance for Various Heater Sizes	9
12.8.	Number of Thermal Cycles as a Function of Rate of Temperature Change	17
13.	Tables	9
13.1.	Chamber Technology Comparison	9
13.2.	LN2 Storage Options	11
13.3.	Screening Parameters	14
13.4.	Product and Fixturing	14
13.5.	Parameters for Screening Systems QRS-410 Chamber	14
13.6.	Load Values for Product and Fixturing	15
13.7.	Three Stress Screening Scenarios	17
13.8.	Base Parameters for Stress Screen Technology Comparison	18
13.9.	Case 1: Dual Cascade Single Zone Chamber	19
13.10.	Case 2: Single Cascade Dual Zone Chamber	20
13.11.	Case 3: LN2 Cooled Single Zone Chamber	21
13.12.	Three Stress Screening Scenarios with Results Compared	21
13.13.	Mechanical Refrigeration Coil Loads	23
13.14.	Chamber Liner and Box Loads	23
13.15.	System Factors for HALT/HASS Chambers	23
13.16.	Holding BTU Leakage for QRS400/410T Chambers	23
13.17.	Specific Heats of Common Materials	24
13.18.	Microbulk Model Specifications	25