A review of lead-free solders for electronics applications

A review on thermal cycling and drop impact reliability of SAC solder joint in portable electronic products

An ‘aldol’ reaction is the reaction of one carbonyl compound, acting as a nucleophile in the form of its enol or enolate derivative, with another, acting as an electrophile. The two carbonyl compounds may or may not be the same. The general reaction is subject to either acid or base catalysis. The initial product is a β-hydroxycarbonyl compound. Under some conditions, this primary product undergoes dehydration, resulting in an α,β-unsaturated carbonyl compound. In this chapter, we summarize the aldol reaction from a historical perspective and point out the limitations of the reaction as it was generally used prior to about 15 years ago.1 Succeeding chapters treat the aldol reaction as it is usually practiced today, in a ‘directed’ manner, using ‘preformed’ enolates.2 As will be seen in the sequel, an understanding of the factors regulating the stereochemistry of the aldol reaction has been largely responsible for the rebirth of this venerable reaction in the last 15 years.3

1.5 – The Aldol Reaction: Acid and General Base Catalysis

Sn-Ag-Cu (SAC) alloy is currently recognized as the standard lead-free solder alloy for packaging of interconnects in the electronics industry, and high- Ag-content SAC alloys are the most popular choice. However, this choice has been encumbered by the fragility of the solder joints that has been observed in drop testing as well as the high cost of the Ag itself. Therefore, low-Ag-content SAC alloy was considered as a solution for both issues. However, this approach may compromise the thermal-cycling performance of the solders. Therefore, to enhance the thermal-cycling reliability of low-Ag-content SAC alloys without sacrificing their drop-impact performance, alloying elements such as Mn, Ce, Ti, Bi, In, Sb, Ni, Zn, Al, Fe, and Co were selected as additions to these alloys. However, research reports related to these modified SAC alloys are limited. To address this paucity, the present study reviews the effect of these minor alloying elements on the solder joint reliability of low-Ag-content SAC alloys in terms of thermal cycling and drop impact. Addition of Mn, Ce, Bi, and Ni to low-Ag-content SAC solder effectively improves the thermal-cycling reliability of joints without sacrificing the drop-impact performance. Taking into consideration the improvement in the bulk alloy microstructure and mechanical properties, wetting properties, and growth suppression of the interface intermetallic compound (IMC) layers, addition of Ti, In, Sb, Zn, Al, Fe, and Co to low-Ag-content SAC solder has the potential to improve the thermal-cycling reliability of joints without sacrificing the drop-impact performance. Consequently, further investigations of both thermal-cycling and drop reliability of these modified solder joints must be carried out in future work.

High-Reliability Low-Ag-Content Sn-Ag-Cu Solder Joints for Electronics Applications

A collection of 250 foliar endophytes of Picea glauca (white spruce) yielded several isolates that produced metabolites toxic to Choristoneura fumiferana (spruce budworm). Three of these strains were selected for further study based on their ability to be cultured and produce secondary metabolites under laboratory conditions. The culture filtrate of each was extracted and analyzed by LC-MS and LC-NMR, and the major metabolites were isolated and characterized. Structures were elucidated by spectroscopic analyses including 2D NMR and HRMS and by comparison to literature data. In some cases the extract was methylated in order to facilitate separation, but the original natural structure was determined by comparing the NMR data of the isolated methylated product with that of the stop-flow NMR of the underivatized extract (i.e., 2a, 2b, and 4). Two of these metabolites, 1 and 2a, are new structures, 3 and 4 are reported here for the first time as fungal metabolites, and 5−10 as known fungal metabolites from oth...

Characterization of polyketide metabolites from foliar endophytes of Picea glauca.

In this study, the reliabilities of low Ag SAC alloys doped with Mn or Ce (SACM or SACC) were evaluated under JEDEC drop, dynamic bending, thermal cycling, and cyclic bending test conditions against eutectic SnPb, SAC105, and SAC305 alloys. The Mn or Ce doped low cost SAC105 alloys achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for some test conditions. More significantly, being a slightly doped SAC105, both SACM and SACC matched SAC305 in thermal cycling performance. In other words, the low cost SACM and SACC achieved a better drop test performance than the low Ag SAC alloys plus the desired thermal cycling reliability of high Ag SAC alloys. The mechanism for high drop performance and high thermal cycling reliability can be attributed to a stabilized microstructure, with uniform distribution of fine IMC particles, presumably through the inclusion of Mn or Ce in the IMC. The cyclic bending results showed SAC305 being the best, and all lead-free alloys are equal or superior to SnPb. The reliability test results also showed that NiAu is a preferred surface finish for BGA packages over OSP.

Achieving high reliability low cost lead-free SAC solder joints via Mn or Ce doping

In this study, the reliabilities of low Ag SAC alloys doped with Mn or Ce (SACM or SACC) were evaluated under JEDEC drop, dynamic bending, thermal cycling, and cyclic bending test conditions against eutectic SnPb, SAC105, and SAC305 alloys. The Mn or Ce doped low cost SAC105 alloys achieved a higher drop test and dynamic bending test reliability than SAC105 and SAC305, and exceeded SnPb for some test conditions. More significantly, being a slightly doped SAC105, both SACM and SACC matched SAC305 in thermal cycling performance. In other words, the low cost SACM and SACC achieved a better drop test performance than the low Ag SAC alloys plus the desired thermal cycling reliability of high Ag SAC alloys. The mechanism for high drop performance and high thermal cycling reliability can be attributed to a stabilized microstructure, with uniform distribution of fine IMC paricles, presumably through the inclusion of Mn or Ce in the IMC. The cyclic bending results showed SAC305 being the best, and all lead-free alloys are equal or superior to SnPb. The reliability test results also showed that NiAu is a preferred surface finish for BGA packages over OSP.

Shock resistant and thermally reliable low Ag SAC solders doped with Mn Or Ce

Biomimetic syntheses of pretetramides. 3. Synthesis of 6-methylpretetramides using a preassembled D ring template.

In the study, a proprietary strain-controllable dynamic bending method was adopted to verify the memory package effects on the solder joint reliability in the PoP package, instead of electrical resistance monitoring in the JESD22-B111 using mechanical shock testing of package on board at a single shock pulse for handheld electronic device dropping simulation. Two test vehicles were designed for comparison. One is flip chip BGA as bottom package with memory package stacked on the top, another one is same flip chip BGA package. The PoP package with SnAgCu based interconnection on the bottom and top package underperformed same bottom flip chip BGA package in terms of solder joint life between package and PCB in the dynamic bending test, which illustrated the top memory package will affect adversely the solder joint reliability of bottom package.

J. Y.-C. Lee

Papers

Achieving high reliability low cost lead-free SAC solder joints via Mn or Ce doping

Shock resistant and thermally reliable low Ag SAC solders doped with Mn Or Ce

Biomimetic syntheses of pretetramides. 3. Synthesis of 6-methylpretetramides using a preassembled D ring template.

A Dynamic Bending Method for PoP Package Board Level Reliability Validation

Biomimetic Syntheses of Pretetramides. Part 2. A Synthetic Route Based on a Preformed D Ring.