Transmission electron microscopy studies of interfacial reactions and void formation in lead-free solders with minor elements

Electroless nickel (Ni–P) is a common surface finish used in the ball grid array (BGA) package and interfacial reactions between its surface finish and lead-free solders can form complex intermetallic compound (IMC) layers. The presence of minor elements in lead-free solders either intentionally added or due to impurity contamination during solder manufacturing, can affect the solder-joint performance. In this work, interfacial reactions between Ni–P surface finish and the Sn–Ag–Cu solders were modified by varying Ag and Cu contents and also by adding a small amount of minor elements such as phosphorus (P), indium (In), and germanium (Ge). A transmission electron microscope was used to determine the intermetallic layer phases, compositions, crystal structures, and void defects. Varying the solder alloy elements led to the modulation of voids formation.

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Effect of Multiple Reflows on the Interfacial Reactions and Mechanical Properties of an Sn-0.5Cu-Al(Si) Solder and a Cu Substrate

Materials ◽

10.3390/ma14092367 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2367

Author(s):

Junhyuk Son ◽

Dong-Yurl Yu ◽

Yun-Chan Kim ◽

Shin-Il Kim ◽

Min-Su Kim ◽

...

Keyword(s):

Mechanical Properties ◽

High Heat ◽

Interfacial Reactions ◽

Future Application ◽

Scanning Calorimetry ◽

Cross Sectional ◽

Automotive Electronic ◽

Transmission Electron ◽

Si Content ◽

Lead Free Solders

In this study, the interfacial reactions and mechanical properties of solder joints after multiple reflows were observed to evaluate the applicability of the developed materials for high-temperature soldering for automotive electronic components. The microstructural changes and mechanical properties of Sn-Cu solders regarding Al(Si) addition and the number of reflows were investigated to determine their reliability under high heat and strong vibrations. Using differential scanning calorimetry, the melting points were measured to be approximately 227, 230, and 231 °C for the SC07 solder, SC-0.01Al(Si), and SC-0.03Al(Si), respectively. The cross-sectional analysis results showed that the total intermetallic compounds (IMCs) of the SC-0.03Al(Si) solder grew the least after the as-reflow, as well as after 10 reflows. Electron probe microanalysis and transmission electron microscopy revealed that the Al-Cu and Cu-Al-Sn IMCs were present inside the solders, and their amounts increased with increasing Al(Si) content. In addition, the Cu6Sn5 IMCs inside the solder became more finely distributed with increasing Al(Si) content. The Sn-0.5Cu-0.03Al(Si) solder exhibited the highest shear strength at the beginning and after 10 reflows, and ductile fracturing was observed in all three solders. This study will facilitate the future application of lead-free solders, such as an Sn-Cu-Al(Si) solder, in automotive electrical components.

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Experimental wetting dynamics study of eutectic and lead-free solders varying flux, temperature and surface finish metallization

IEEE/CPMT/SEMI 29th International Electronics Manufacturing Technology Symposium (IEEE Cat. No.04CH37585) ◽

10.1109/iemt.2004.1321632 ◽

2004 ◽

Cited By ~ 1

Author(s):

Suk Chae Kang ◽

Chunho Kim ◽

J. Muncy ◽

M. Schmidt ◽

D. Baldwin

Keyword(s):

Surface Finish ◽

Lead Free ◽

Lead Free Solders ◽

Wetting Dynamics

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Interfacial reactions between Sn–8Zn–3Bi–xNi lead-free solders and Cu substrate during isothermal aging

Materials Chemistry and Physics ◽

10.1016/j.matchemphys.2010.05.028 ◽

2010 ◽

Vol 123 (2-3) ◽

pp. 629-633 ◽

Cited By ~ 13

Author(s):

Lijuan Liu ◽

Wei Zhou ◽

Baoling Li ◽

Ping Wu

Keyword(s):

Isothermal Aging ◽

Interfacial Reactions ◽

Lead Free ◽

Cu Substrate ◽

Lead Free Solders

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Interfacial reactions of Sn–58Bi and Sn–0.7Cu lead-free solders with Alloy 42 substrate

Microelectronics Reliability ◽

10.1016/j.microrel.2013.09.003 ◽

2014 ◽

Vol 54 (1) ◽

pp. 233-238 ◽

Cited By ~ 8

Author(s):

Yee-Wen Yen ◽

Ruo-Syun Syu ◽

Chih-Ming Chen ◽

Chien-Chung Jao ◽

Guan-Da Chen

Keyword(s):

Interfacial Reactions ◽

Lead Free ◽

Lead Free Solders

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The formation of intermetallic layer structure of SAC405/Cu and SAC405/ENImAg solder joint interfaces

Soldering & Surface Mount Technology ◽

10.1108/ssmt-03-2019-0009 ◽

2020 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Rabiatul Adawiyah Mohamed Anuar ◽

Saliza Azlina Osman

Keyword(s):

Shear Strength ◽

Surface Finish ◽

Printed Circuit Boards ◽

Solder Joints ◽

Layer Structure ◽

Ageing Time ◽

Intermetallic Layer ◽

Electroless Nickel ◽

Optical Microscope ◽

Content Type

Purpose The surface finish is an essential step in printed circuit boards design because it provides a solderable surface for electronic components. The purpose of this study to investigate the effects of different surface finishes during the soldering and ageing process. Design/methodology/approach The solder joints of Sn-4.0Ag-0.5Cu/Cu and Sn-4.0Ag-0.5Cu/electroless nickel/immersion silver (ENImAg) were investigated in terms of intermetallic (IMC) thickness, morphology and shear strength. The microstructure and compositions of solder joints are observed, and analyzed by using scanning electron microscopy (SEM-EDX) and optical microscope (OM). Findings Compounds of Cu6Sn5 and (Cu, Ni)6Sn5 IMC were formed in SAC405/Cu and SAC405/ENImAg, respectively, as-reflowed. When the sample was exposed to ageing, new layers of Cu3Sn and (Ni, Cu)3Sn5 were observed at the interface. Analogous growth in the thickness of the IMC layer and increased grains size commensurate with ageing time. The results equally revealed an increase in shear strength of SAC405/ENImAg because of the thin layer of IMC and surface finish used compared to SAC405/Cu. Hence, a ductile fracture was observed at the bulk solder. Overall, the ENImAg surface finish showed excellent performance of solder joints than that of bare Cu. Originality/value The novel surface finish (ENImAg) has been developed and optimized. This alternative lead-free surface finish solved the challenges in electroless nickel/immersion gold and reduced cost without affecting the performance.

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