Citation: Liang, K.; Wang, Y.; He, Z.
Experimental and Statistical Study of
the Fracture Mechanism of
Sn96.5Ag3Cu0.5 Solder Joints via Ball
Shear Test. Materials 2022, 15, 2455.
https://doi.org/10.3390/
ma15072455
Academic Editor: Alessandro Pirondi
Received: 27 February 2022
Accepted: 23 March 2022
Published: 26 March 2022
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Article
Experimental and Statistical Study of the Fracture Mechanism
of Sn96.5Ag3Cu0.5 Solder Joints via Ball Shear Test
Kun Liang
1,
*, Yuexing Wang
1,2
and Zhigang He
3
1
Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621999, China;
soceity@mail.nwpu.edu.cn
2
Microsystem and Terahertz Research Center, China Academy of Engineering Physics, Chengdu 610200, China
3
The Center of Metrology and Testing, China Academy of Engineering Physics, Mianyang 621999, China;
phyhezhigang@163.com
* Correspondence: liangkun_mtrc@caep.cn
Abstract:
Ball shear testing is an efficient approach to investigate the mechanical reliability of solder
joints at the structural level. In the present study, a series of low-speed ball shear tests were conducted
to study the deformation and fracture characteristics of Sn96.5Ag3Cu0.5 solder joints at continuous
speeds from 10
µ
m/s to 200
µ
m/s. In order to account for randomness, the quantity of tests was
repeated for each shear rate. The relationship between mechanical properties and shear speeds
was calculated in detail via effective statistical analysis. In addition, by utilizing SEM imaging and
ingredient analysis the interfacial effect and fracture mechanism of solder balls were obtained and
their fracture mode classified into two types, viz., bulk fracture and interface fracture. Furthermore,
by means of statistical analysis and approximate calculation it was proven that bulk fracture balls
have greater adhesive powers and reliability compared with interface fracture balls.
Keywords:
Sn96.5Ag3Cu0.5; ball shear test; statistical analysis; SEM image; fracture mechanism; reliability
1. Introduction
Due to human health and environmental concerns the use of lead-free solder materials,
especially Sn-based solder alloys, have been widely used in interconnecting structures
in the microelectronic packaging industry [
1
–
5
]. However, Sn-based materials exhibit
obvious viscoplasticity at room temperature due to their low melting point, such that room
temperature can be considered a ‘high’ temperature [
6
]. In addition, when compared with
traditional lead-containing solders the reliability and stability features of these lead-free
solder alloys under complex loadings, such as thermal cycling and mechanical stresses,
are not quite clear. Furthermore, given the trend toward the miniaturization of electronic de-
vices, the typical dimensions of solder joints has been decreased to several microlengths [
7
],
at which solder joints show obvious size effects and anisotropy [
8
,
9
]. Taking all these factors
into consideration, it is recognized that how to intuitively and rapidly estimate the strain
strength and reliability levels of these high density packaged lead-free solders represents
an important research direction.
In the context of in situ mechanical test approaches for solder joints, the most uni-
versal experimental method is ball shear testing. Its popularity is derived from its simple
testing procedure and explicit experimental mechanism [
10
,
11
]. Although a great deal of
research based on this experimental method has been conducted in the field of BGA solders,
these research works mainly focus on solder ball materials and manufacturing processes.
Their major task has been to distinguish the shear stress characteristics of tested solder
balls under various different conditions, including alloy element proportions [
2
,
12
–
15
],
manufacturing processes [
16
,
17
], solder ball dimensions [
18
,
19
], aging time [
18
,
20
], surface
finish materials [
1
,
21
,
22
], and more. These research efforts have provided effective support
Materials 2022, 15, 2455. https://doi.org/10.3390/ma15072455 https://www.mdpi.com/journal/materials
