Wire bonding method is one of the most important interconnection techniques in electronics packaging. It is used to make electrical contact between integrated circuits or other semiconductor devices and the circuit board during device fabrication.
To evaluate the reliability of this interconnection technique in particular applications, an integrated electromagnetic, thermal and structural analysis is necessary.
An EMS Magnetostatic simulation coupled to thermo-structural analysis is performed to study the failure behavior of a wire bonding connection. The model studied consists of a 300 µm thick wire connecting two copper layers on a common aluminum substrate.
The wire loop geometry is illustrated in Figure 2a - the height H is the distance from the top of the wire to the substrate; the bond length L is defined as the foot to foot distance (dimension presented in Table 1). The present example aims to determine the magnitude of wire deflection in its critical high temperature zone.
Dimensions | Aluminum substrate | Copper layer | Wire |
Length(mm) | 43 | 15 | 9 |
Height(mm) | 1 | 0.3 | 3 |
Width(mm) | 25 | 15 | 0.3 (Diameter) |
The Magnetostatic module of EMS, coupled to steady state thermal and structural analysis, is used to compute and visualize magnetic results, temperature distribution and mechanical deformation of the wire.
To perform an analysis using EMS, the following important steps need to be performed:
In our case study, the following properties of material are used (Table 2):
Part | Density (Kg/ |
Relative permeability | Electrical conductivity (S/m) |
Specific heat capacity (J/Kg. K) |
Thermal conductivity (W/m. K) |
Elastic Modulus (Pa) |
Poisson’s ratio | Thermal expansion coefficient (/K) |
Wire (Al-H11) | 2700 | 1 | 3.57 E+07 | 897 | 230 | 71.8 E+09 | 0.33 | 25.3 E-06 |
Alumina substrate |
3690 | 1 | 0 | 687 | 24.7 | Not required |
||
Copper layers | 8900 | 0.99 | 5.7 E+07 | 390 | 385 |
The wire is defined as a solid coil carrying a 10A DC current.
Initial temperature applied to both bonded feet of the wire is set to 300 K. The thermal convection inputs for the ambient air body:
-The initial (ambient) temperature of the simulation is set to 300 K
-Convection coefficient on the surrounding air is set to 10 W/m² K
Fixed boundary conditions are applied to both feet of the bonded wire and to the four faces of each DCB substrate, as shown in the figure 3:
A mesh Control was applied on the wire for a finer meshing, as it is the most important component in the analysis, for a better results accuracy in this part, (Figure 4).
The simulation results include: magnetic flux density, magnetic field intensity, applied current density, temperature and heat flux distribution, mechanical displacement, stress, etc.
EMS offers the possibility to visualize results as 3D plots and curves. The figure below illustrates the distribution, in a vector plot, of the applied current density between the two bonded feet of the wire.
The Table 3 contains the DC resistance of the simulated wire which is computed and generated by EMS in the results table.
Resistance (ohms) | |
Solid Coil | 4.8532 E-0.003 |
The Figure 6 shows the temperature distribution in the wire that achieves a maximum value of 340 K.
The maximum of temperature is located in the peak point of the wire due to the current concentration in this location. This high temperature zone will also experience the maximum mechanical deflection as shown in the Figure 7. Table 4 displays a comparison between EMS and reference results.
EMS | Reference [2] | |
Temperature (Kelvin) | 340 | 337 |
Figure 8 shows the displacement plot results generated by EMS, in the bonded wire, which correlate very well with the reference results.
This example presents an EMS numerical evaluation of the performance of a bonding wire case. It enables a better estimation of the fatigue the wire will sustain during its lifetime. The obtained results show a very good agreement with the reference [2] for both structural and thermal analysis.
[1]. https://www.we-online.com/web/en/wuerth_elektronik/start.php
[2]. Dagdelen, Turker. "Failure analysis of thick wire bonds. MS thesis". University of Waterloo, 2013.
[3]. Dagdelen, Turker, Eihab Abdel-Rahman, and Mustafa Yavuz. "Reliability Criteria for Thick Bonding Wire." Materials 11.4 (2018): 618.