Guidelines for Accelerated Reliability Testing of Surface ...

1 ASSOCIATION CONNECTING. ELECTRONICS INDUSTRIES. IPC-SM-785. Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments IPC-SM-785. November 1992 A guideline developed by IPC. 2215 Sanders Road, Northbrook, IL 60062-6135. Tel. Fax IPC-SM-785 November 1992. Table of Contents SCOPE .. 1 Creep Rupture 33. 1 Mechanical Shock 34. Document Organization .. 1 Failure Criteria for Solder Joint Fatigue Tests .. 34. APPLICABLE DOCUMENTS .. 2. Accelerated Life Test Planning .. 35. 2. Failure Mode 38. Joint Industry Standards .. 2. Reporting 41. 2. Other 2 Appendix A Step-by-Step Example .. 43. REQUIREMENTS Appendix B References .. 45. Terms and 3 Appendix C Bibliography .. 46. Reliability Concepts and 5. Reliability Assurance .. 6 Figures Damage/Failure Mechanisms .. 10 Figure 1 Flowchart for 4. Application 12 Figure 2 Generic Reliability bathtub'' curves comparing electronic components and Surface mount Surface MOUNT SOLDER ATTACHMENT solder attachment.

2 6. FATIGUE BEHAVIOR AND Reliability Figure 3 Generic cumulative failure probabilities for PREDICTION .. 15 electronic component and Surface mount General Fatigue Life Models .. 15 solder attachment .. 7. Solder Joint 15 Figure 4 Flow chart for Surface mount solder attachment Reliability assurance .. 8. Fatigue Behavior of Solder 16. Figure 5 Cumulative fatigue 10. Acceleration Factors/Acceleration Figure 6 SMT assembly thermo-mechanical Transform .. 19. deflections resulting from thermal gradients Statistical 20 in thermal shock .. 13. Figure 7 Thermal cycle/fatigue mechanisms DESIGN FOR SOLDER ATTACHMENT for 18. Reliability .. 22. Figure 8 Shear strengths of 60:40 SnPb solder as Primary Design Parameters .. 22 a function of temperature and strain rate .. 28. Secondary Design Parameters .. 23 Figure 9 Creep behavior of solder .. 34. MANUFACTURE/PROCESSES.

3 24 Figure 10 Example of circuit layout .. 36. Figure 11 Internal lead connection schemes for Process Control and Verification .. 24. odd lead numbers per 37. Consequences of 24. Material 27 Tables Accelerated Reliability Testing Table 1 Worst-Case Use Environments for Surface Mounted Electronics and Recommended Reliability Program/Strategy .. 30 Accelerated Testing .. 14. Generic Damage Mechanism 30 Table 2 Equivalent Mean Accelerated Test Cycles .. 21. Thermal Cycling .. 30 Table 3 Typical Values .. 29. Mechanical Cycling .. 32 Table 4 Properties of Printed Board 31. 32 Table 1A Results of Accelerated Reliability Test .. 43. iv September 1992 IPC-SM-785. Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments SCOPE cyclic loads during large temperature excursions or high This document provides Guidelines for Accelerated reliabil- frequency cycles at low temperatures.

4 Also discussed are ity Testing of Surface mount solder attachments and for the acceleration factors, the acceleration transforms, and evaluating and extrapolating the results of these Accelerated statistical considerations. Reliability tests towards actual use environments of elec- Section 5, Design for Solder Joint Reliability ''. tronic assemblies. Background and design information is This section details the various design parameters that provided for an understanding of the Accelerated test have a primary influence on solder attachment fatigue issues. Reliability . All aspects of the solder joint formation are Purpose The purpose of Accelerated Reliability test- addressed including component size, lead stiffness, coef- ing is to provide confidence that the design and the ficient of thermal expansion, solder joint uniformity, as manufacturing/assembly processes are capable of meeting well as solder composition, grain structure and the value the intended goals of product performance.

5 These guide- that conformal coating or compliant layers provide to the lines provide adequate commonality and validity for accel- attachment system. erated Reliability tests: Section 6, Manufacturing Processes''. To allow comparison of results from different test pro- This section provides the relationship between the assem- grams bly and attachment processes, including their control and verification, and the resultant defects or potential defects To provide the generic technical understanding of the underlying issues necessary to the design for adequate from the original processes or touch-up, rework or repair Reliability actions. Material properties of solder (including volume), components, printed boards, adhesives and conformal To permit the analytical prediction of Reliability based on coatings are discussed as to their interrelationships and a generic database and technical understanding the impact that these characteristics have on the manufac- To reduce cost and avoid time-consuming Testing of every turing processes.

6 Design iteration Section 7, Accelerated Reliability Testing ''. To establish practical alternatives to replace the exces- This section deals with the goals of Accelerated Testing to sively long test durations necessary to verify Reliability of produce a failure in the shortest time using techniques products subject to severe use environments or low fail- intended to simulate the use environment in order to ure tolerances establish the appropriate confidence level of product per- formance. Various types of stress cycling are reviewed Document Organization This document has been and correlated to damage mechanisms. Also discussed is organized to provide the reader with consistent information the need for developing a strategy which includes a test on the various aspects of Reliability and identifies the parameters that need to be addressed. Each section serves plan, sampling methodology, test vehicles, and failure a specific function in the Reliability description chain.

7 Mode analysis. Where appropriate, references are provided as to where Appendix A, Step-by-Step Example''. additional information may be obtained. This section shows illustrations of applying the principles Section 3, Requirements'' detailed in the information provided in this publication. This section provides an overview of the concepts of reli- Numerical examples are provided that highlight the rela- ability and all of the characteristics that need to be con- tionship of the various parameters. sidered in the validation of a product design. Included are Appendix B, References''. the definitions of the appropriate terms, as well as generic This section provides reference to published information models for fatigue life and failure probability, manufac- that has a bearing on solder joint Reliability and is refer- turing process flow, use environments, and Testing meth- enced in the body of the text of this document.

8 Details are odology. shown as to Title, Author, and Publisher. Section 4, Surface Mount Solder Attachment Fatigue Appendix C, Bibliography''. Behavior and Prediction'' This section provides references to additional published This section deals with the fatigue life models for solder information that could be of use to the practitioner. The joints including their behavior when subjected to multiple references are organized into three major topics 1.