Study on Optimization of Fatigue Test of Nanosilver Solder

Hui Yang

, Yang Zhang

and Ji hui Wu

School of mechanical and control engineering, Guilin University of Technology

Keywords: Nano silver paste, sintering, mechanical fatigue test, cycle life.

Abstract: Nanosilver solder paste due to its high melting point, low sintering temperature and good electrical/thermal

conductivity and mechanical reliability Sex, more and more attention by the electronic packaging industry.

And, as a new type of lead-free thermal interface Materials, nano-silver solder paste has the potential to

gradually replace traditional solder and conductive silver paste, used in high-temperature power electronics

In the device packaging, according to the isothermal mechanical fatigue test, a temperature-dependent

fatigue life prediction model is proposed, and the cycle life of the nanosilver solder paste lap joint at

different temperatures is accurately predicted.

1.NANO-SILVERSOLDER PASTE

SINTERING

At present, due to the low-temperature sintering

characteristics of nano-silver particles, nano-silver

has been widely used in the electronic field, such as

low-temperature connection process, inkjet printing

technology, metal-metal bonding, etc. . CP Wong et

al. applied the low-temperature sintering

characteristics of nanosilver to ECAS[1,2]. It was

found that the surface chemistry of nanosilver

particles played an important role in the low-

temperature sintering of nanosilver. The low-

temperature pyrolysis of surface organics can

achieve the nanosilver particles in the conductive

paste. Sintered below 200°C . Fuller et al. introduced

an ink-jet technology based on nano-silver and gold

solder pastes for the production of conductive metal

lines on a substrate. The solder paste has good flow

ability and low viscosity. The results of the study

show that when the sintering temperature is as low

as 300°C, a metal line with high conductivity can be

obtained In addition, nanosilver paste can also be

printed on flexible substrates Bell et al. prepared a

silver paste containing nano-scale and micro-scale

mixed silver particles, and evaluated the sintering

process with an operating temperature lower than

250°C by measuring the conductivity .

2. FAILURE FORM

Reliability of Solder Joints in Electronic Packaging

The failure of semiconductors and microelectronic

devices is often the result of factors such as thermal,

mechanical, electrical, and chemical, either alone or

in combination. Therefore, failures of electronic

devices can be classified into thermal/mechanical

failures, electro-failures, and electrochemical effects.

Since most of the failures in the package structure

are caused by the mechanical failure of the

connection material, the reliability of the electronic

package is mostly focused on the thermal

mechanical properties of the solder joints [3,4]

3.STUDY AND EXPERIENCCE

3.1 Experimental Method

The nano-silver solder paste lap joint structure

used was tested on a miniature uniaxial fatigue tester.

The test ambient temperature was provided by an

external heating furnace. The isothermal mechanical

fatigue study uses a symmetric cyclic displacement

control method to apply load to the joint. The

waveform uses triangular waves[5,6].The loading

conditions for isothermal fatigue test of sintered

nano-silver joints are shown in Table 1. The

displacement rate control in the test was 2.07×

−

mm/s. In the isothermal mechanical fatigue test,

joint damage continues to accumulate under cyclic

loading, and the ability of the joint to withstand

deformation gradually decreases. Therefore, under

the conditions of constant displacement amplitude,

the measured load response of the joint will be

continuously tested. reduce. Therefore, the decrease

of the bearing capacity in the joint fatigue cycle

indicates the joint fatigue resistance at different

temperatures and displacement amplitudes. In this

study, the number of cycles when the joint was

finally broken was used as the fatigue life.solomon

has suggested that the fatigue damage accumulation

proces of materials under reciprocating loads can use

load reduction factors[6].

To represent. Its definition is as follows:





=−



（3-1）

Among them,

p

is the loading stress range for

a cycle,The maximum loading stress range is

p

.According to the definition of load reduction

factor, it is believed that in the cyclic process, the

continuous action of the load causes the

accumulation of damage within the joint, the

carrying capacity of the material is continuously

declining, and the load factor gradually increases.

When 0, the material or structure is considered to be

completelydestroyed [7].

Table 3-1 Isothermal fatigue test loading conditions of

sintered nano-silver joints.

3.2 Effect of Temperature on Isothermal

Fatigue Behavior of Sintered

Nanosilver Joints

In order to study the effect of different ambient

temperature on the fatigue behavior of sintered

nano-silver joints, the displacement amplitude

Symmetrical cyclic fatigue tests at different

temperatures under 5.18×

−

mm conditions,Table

Figure 3-1 shows the stress response of the joint at

different temperatures as a function of the number of

cycles . As can be seen from the line, the peak stress

and cycle life that the joint .Under low temperature

conditions, the fracture of the joint suddenly occurs

after a certain number of cycles, and as the

temperature rises, the joint undergoes a continuous

decline in the carrying capacity of the joint

beforebreaking.

Fig.3-1 Fatigue test for displacement amplitude of 5.18×

−

mm at temperature of: (a) 25℃; (b) 125℃; (c)

225℃; (d) 275℃; (e) 325℃.

As can be seen from the figure, both the

increase in the amplitude of the displacement and

the increase in the ambient temperature Reduce the

cycle life of the joint.

4.EXPERIMENTAL RESULTS AND

ANALYSIS

In order to verify the predictive power of the

model, the determined model parameters are brought

into equation and the displacement amplitudes are

both5.18 ×

−

mm, the isothermal mechanical

fatigue life of the sintered nano-silver structures with

different test ambient temperaturesis

predicted[8] .The relationship between the predicted

lifetime and temperature is shown in 3-1 It can be

seen from the figure that the fatigue life prediction

model based on structural displacement has a good

prediction of jointfatigue life at different

temperatures.

Fig.4-1Fatigue life versus temperature for structure

displacement amplitude of 5.18×

−

Compare the measured lifetime and predicted

lifetime of sintered nano-silver bonding structures

obtained in the test From Fig. 4-2, it can be seen that

the proposed temperature-dependent fatigue life

prediction model based on structure displacement is

The test results are within the double dispersion

band. The predicted results of this model are in good

agreement with the experimental results, indicating

that the model It can be used to predict the fatigue

life of sintered nano-silver structures at different

temperatures.

Fig. 4-2 Comparison of predicted and fatigue life

5. CONCLUSIONS

At 325°C, microscopic cracks formed in the

grains of the joints are formed as a result of the

cyclic action.the expansion begins, resulting in a

progressive reduction of the load bearing capacity of

the sintered nanosilver joints from the beginning of

the Cycle [8]. Falling, so the load drop at high

temperatures is evident at lower

temperatures,especially at relatively high

displacement amplitude levels.

In this process, the micro-cracks in the joints

start to sprout gradually, absorbing a certain amount

of energy and keeping the joints at a certain stress

level. Subsequently, the fatigue cracks rapidly

expanded, and the load-bearing capacity of the joints

dropped to a level close to zero, resulting in

breakage of the joints. In general, the initiation and

propagation of cracks in the joints leads to a

decrease in the effective load-bearing area of the

joints. Therefore, the stress required to maintain

constant joint deformation also decreases. The

optimization prediction method can effectively

predict the mechanical fatigue life, and has

important guiding significance for the subsequent

research on the sintered nano-silver structure.

REFERENCES

1. Xing H., Keller S., Wu Y.F., et al.Gallium nitride

based transistors ， Journal of Physics: Condensed

Matter, 2001, 13: 7139~7157

2. Cyril B., Dominique P., Bruno A., et al., State of the

art of high temperature power electronics, Materials

Science and Engineering: B, 2011,

3. Tamor M.A.,Needs for high temperature electronics

for automobiles, Albuquerque,NW: Final Report on

Results of a Survey and Workshop on High-

Temperature.and.RadiationHardened,Electronics,

SAND89-097,A11~A16

4. Harry Kraus. Creep Analysis. New York, USA, 1980.

5. Pradeep L., Michael G. P., Edward B.

H,writing.Translated by Jia Ying, Zhang Dejun and

Liu Rujun, Effects of Temperature on

Microelectronics and System Reliability, Beijing:

National Defense Industry Press,2004

6. TU East, high temperature structural integrity

principle. Beijing: Science Press, 2003

7. Kang G.Z., Gao Q., Yang X.J., Avisco-plastic

constitutivemodelin corporated with cyclic hardening

for uniaxial/multiaxial ratcheting of SS304 stainless

steel at room temperature, Mechanics of Materials,

2002, 34(9):

8. Solomon H.D., Low cycle fatigue of 60/40 solder-

plastic strain limited vs displacement limited

testing,ElectronicPackaging-

Materials,Processes,St.Paul,Minnesota,Bloomington;

Minnesota, USA, 2007, 29~31

9. Guo Z., Sprecher A.F., Conrad H., Crack initiation

and growth during low,cycle fatigue of Pb-Sn solder

joints, Electronic Components and Technology

Conference, 2011,