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High Thermo-Mechanical Fatigue and Drop Shock Resistant Alloys



High Thermo-Mechanical Fatigue and Drop Shock Resistant Alloys
High-Ag, low-Ag: Which alloy fits best certain application? Here we present a report on the thermal and mechanical reliability of alloys.
Materials Tech

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Authored By:


Morgana Ribas, Ph.D., Suresh Telu, Ph.D., Prathap Augustine, Raghu R. Rangaraju, Anil Kumar, Divya Kosuri, Pritha Choudhury, Ph.D., Siuli Sarkar, Ph.D.
Alpha Assembly Solutions
Bangalore, KA, India

Rommel T. Bumagat, Garian Lim
Alpha Advanced Materials
14 Joo Koon Crescent, Singapore

Martin Sobczak
Alpha Advanced Materials
Suwanee, GA, USA

Summary


High-Ag, low-Ag, high-Ag plus additives: Which alloy fits best certain application? Here we present a comprehensive report on the thermal and mechanical reliability of alloys ranging from 0.3 to 3.8% Ag, with and without presence of additives such as Bi, Ni and Sb. CTBGA packages with 84 I/Os were assembled using Sn-1Ag-0.5Cu, Sn-0.3Ag-0.7Cu-X, Sn-1.2Ag-0.5Cu-0.05Ni, Sn-3Ag-0.5Cu, Sn-3.8Ag-0.7Cu-Sb-Bi-X and Sn-3.8Ag-0.8Cu-Bi-X spheres. Test vehicle assembly used Sn-3Ag-0.5Cu solder paste for all alloys, except for Sn-3.8Ag-0.8Cu-Bi-X BGAs, which were evaluated with both Sn-3Ag-0.5Cu and Sn-3.8Ag- 0.8Cu-Bi-X solder pastes. Single ball shear, drop shock and thermal cycling were used to evaluate these alloys performance for BGA packages applications. Our results expand the perspective over the usual belief that high-Ag Sn-Ag-Cu alloys result in better thermal cycling and lower drop shock performance than when using low-Ag alloys.

Alloying additions can be used to improve single ball shear, drop shock and thermal cycling properties. In order to obtain maximum performance and cost benefit, solder alloys need to be paired to the correct application. Based on the results shown, we recommend: i) Sn-0.3Ag-0.7Cu-X for applications that require maximum drop shock and reasonable thermal cycling performance. ii) Sn-3Ag-0.5Cu for applications requiring good drop shock and thermal cycling properties. iii) Sn-3.8Ag-0.8Cu-Bi-X for applications that require higher shear strength, drop shock and thermal cycling, including automotive under the hood, high efficiency LEDs and semiconductor packaging.

Conclusions


We have shown here a little broader perspective over the usual belief that higher drop shock performance is achieved using lower-Ag Sn-Ag-Cu alloys, whereas high thermal cycling results from higher-Ag content. By performing a very comprehensive study of six alloys with various degrees of Ag content and additives, we were able to draw the
following conclusions:

Given these results, we conclude that: i) Bi, Sb and other alloying additions can significantly increase single ball shear strength, ii) Sn-0.3Ag-0.7Cu-X and Sn-3.8Ag-0.8Cu-Bi-X presented the highest drop shock performance, which is attributed to additives that control atomic diffusion at the substrate interface and in the bulk solder, iii) Increasing Ag in the solder alloy (e.g., Sn-3Ag-0.5Cu) improves thermal cycling, but its performance can be further improved by combining higher-Ag content and performance additives as shown for Sn-3.8Ag-0.7Cu-Sb-Bi-X and Sn-3.8Ag- .8Cu-Bi-X alloys.

In order to obtain maximum performance and cost benefit, solder alloys need to be paired to the correct application. Among the low-Ag alloys, Sn-0.3Ag-0.7Cu-X (i.e., SACX Plus 0307) provides the best drop shock and thermal cycling performance. Sn-3Ag-0.5Cu provides good drop shock and thermal cycling properties. For applications that require higher thermal reliability performance, including shear strength and thermal cycling, Sn-3.8Ag-0.7Cu-Sb-Bi-X (i.e., Innolot or Maxrel) and Sn-3.8Ag-0.8Cu-Bi-X (i.e., Maxrel Plus) are recommended. In addition to that, Sn-3.8Ag-0.8Cu-Bi-X also delivers excellent drop shock (and vibration) performance, and is particularly recommended for applications such as automotive under the hood, high efficiency LEDs and semiconductor packaging.

Initially Published in the SMTA Proceedings

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