Metallurgical Bond Evaluation Methods Diodes Metallurgical bond e

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Metallurgical Bond Evaluation Methods Diodes Metallurgical bond e

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MicroNote #030
Metallurgical Bond Evaluation Methods Diodes
Metallurgical bond evaluations diodes have been subject interest many years. stimulated additional evaluation tools methods over last decade that still evolving. This MicroNOTE will provide some added background information this topic. Metallurgical bonding requirements Category defined MIL-PRF-19500, Appendix paragraph A.3.19. Destructive Physical Analysis (DPA) procedures also exist determine when bonds acceptable. This involved MIL-STD-1580A revisions entitled "Destructive Physical Analysis Electronic, Electromagnetic, Electromechanical Parts", well method 2101 MIL-STD-750 diodes. some respects, there have been notable differences between them that have also resulted different dispositions DPAs. However with recent changes MIL-STD-1580B including section "Detailed Requirements Glass Bodied Diodes", these methods better support another. will review some previous possible conflicts they resolved. oldest method bond evaluation involving MIL-STD1580A provided cross-sectional analysis with minimum bond criteria available area. separately recognize three different metallurgical bond categories identified MIL-PRF-19500. This criterion have been misleading unless multiple cross-sections were also performed. MIL-STD-750, Method 2101 entitled "DPA Procedures Diodes". supports MIL-PRF-19500 recognizing three metallurgical bond categories their different requirements. Although cross sectioning still included design verification method 2101, intended exclusive disposition bond voids same manner MILSTD-1580A previously did. example, method 2101 also provides scribe-and-break procedure glass-axial-lead surface-mount diodes. also recognizes thermal impedance bond indicator, particularly Category where crosssectional analysis scribe-and-break methods definitive.
Kent Walters Russo
This latter Category example where "diffusion bond" provided only between outermost metallization layer elements being joined defined MIL-PRF-19500M, Appendix Category scribe-and-break method typically reveals strength bond regions showing pulled silicon interface. glass package envelope contacting causes silicon break undesired location, broken device further analyzed described below. "Silver button with braze" construction example specifically defined Method 2101 Category metallurgical bond. Bonding these products Microsemi achieved with braze preforms between plugs. preforms designed melt controlled manner during sealing/braze process. When evaluations were sometimes made with older MIL-STD-1580A, random voids individual cross-sectional planes could appear greater. However when entire removed actual bond measured, there been consistently greater than bonds Microsemi evaluations. This also been confirmed cross sectioning plane (see figures examples) well using additional scribe, break, procedure.
Figure (25% location through die)
Figure (50% location through die)
Figure
itself acceptance tool previously referenced older MIL-STD-1580A done only plane. Cross sectioning single plane useful, standalone method bond evaluation. This handicap also applies other assembly designs including solder-bond contacts defined Category diffused bonds Category III. MIL-STD-750 Method 2101 recognizes these limitations offers other methods confirming bond integrity. This includes scribe-and-break thermal impedance testing ensure thermal transfer qualities die-bond region described MIL-STD-750, Method 3101. These additional analytical tools also cross-referenced latest revision MIL-STD-1580B described earlier.
Figure (75% location through die)
Although requirement Method 2101 scribe break, Microsemi also evaluated each bond scraping digging through bond interfaces. these evaluations reveal bonding areas well beyond requirements Method 2101. demonstrate this, Microsemi evaluated devices that were cross-sectioned from JANS assembly lot. These cross-sectional photos sometimes exhibit bond-area voids single plane that exceed seen figures Microsemi then performed scribe, break, scrape, procedure additional samples evaluate device interfaces such figures taking photo worst interface (figure running imaginary line through various planes simulate cross-section photo, pitfalls cross-sectional analysis
Figure
Figure
There also many other considerations good quality bond analysis when using cross sectioning glass encapsulated voidless construction such those with Tungsten slugs Category bonds. example, scribe-and-break techniques practical bond analysis since silicon will often shatter with these voidless designs. During cross sectioning, particular care must taken prevent inducing voids from slug during initial grinding when micro fracturing silicon silicides occur from variations type abrasive, grinding direction, pressure, etc. Also care must taken prevent crack damage during cross sectioning. more details, refer Microsemi MicroNOTE entitled "Metallographic Cross-Sectioning Techniques Performance Glass Encapsulated Voidless Construction Diodes".
Figure

Metallurgical Bond Evaluation Methods Diodes Metallurgical bond e

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