# Evaluation and thermal ageing of power semiconductor die attachments based on porous film electrodeposition

Goulven Janod, Lucas Chachay, Jonathan Schoenleber, Yvan Avenas, Didier Bouvard, Rémi Daudin, Jean-Michel Missiaen, M.-P. Gigandet, J.-Y. Hihn, R. Khazaka

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Goulven Janod, Lucas Chachay, Jonathan Schoenleber, Yvan Avenas, Didier Bouvard, et al. Evaluation and thermal ageing of power semiconductor die attachments based on porous film electrodeposition. Microelectronics Reliability, 2025, 167, pp.115648. 10.1016/j.microrel.2025.115648. hal-04984517

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Submitted on 10 Mar 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Evaluation and thermal ageing of power semiconductor die
attachments based on porous film electrodeposition

G. Janod<sup>a,b</sup>, L. Chachay<sup>b</sup>, J. Schoenleber<sup>c</sup>, Y. Avenas<sup>a,*</sup>, D. Bouvard<sup>b</sup>, R. Daudin<sup>b</sup>, J-M. Missiaen<sup>b</sup>, M-P. Gigandet<sup>c</sup>, J-Y. Hihn<sup>c</sup>, R. Khazaka<sup>d</sup>

<sup>a</sup> Univ. Grenoble Alpes, CNRS, Grenoble INP, G2Elab, 38000 Grenoble, France

<sup>b</sup> Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMAP, 38000 Grenoble, France

<sup>c</sup> Univ. Franche-Comté, CNRS UTINAM UMR6213-Besançon, France

<sup>d</sup> Safran SA, Safran Tech, 1 rue des jeunes bois, Châteaufort, CS 80112, France

Abstract

Driven by applications in the field of electric mobility, power electronics face the challenge of operating at higher power densities. Power modules with double-side cooling appear as a promising solution, but they are difficult to manufacture. Electrodeposited copper allows flexibility in module design. This paper evaluates a die attachment method based on thermocompression of electrodeposited porous copper films. Films are fabricated using the DHBT (Dynamic Hydrogen Bubble Template) technique. A characterization study of this solution, including its behavior after thermal ageing, is carried out using thermal impedance and shear stress measurements.

# 1. Introduction

The trend in power electronics, and, particularly, in the transportation field, is the increase in power density. In this context, the wire-bonding connection has reached its limitations in terms of thermal management, reliability [1-2], and parasitic inductance [3]. Thus, power modules with double-side cooling, where semiconductor dies are sandwiched between two substrates [4-5], appear to be a promising technology. However, this technology faces several problems, as for example electric field management around the top faces of chips and quality of die attachments to increase the lifetime of power modules. Hence, technologies for connecting electrically and mechanically dies to substrates are still widely under development [6].

Concerning die attachment materials, an efficient technology is silver sintering, as it provides a relatively low temperature process (200 - 250°C) and melts at a much higher temperature (961°C). This process shows excellent thermal, mechanical and electrical properties [7]. For instance, Liu et al. [8] reported a shear strength of between 40 and 60 MPa for dies sintered at 250°C. However, it also presents several drawbacks, such as the cost of silver powders, the criticality of the material [9], and electromigration problems during operation [10]. For all these reasons,

new die attachment methods based on the use of copper are becoming increasingly popular today, even if the oxidation of this metal during process and operation is a limitation to their development. Sintering of copper pastes is therefore under the focus of intense research. Compared to sintered silver, sintered copper presents higher yield strength, lower plastic strain, and a coefficient of thermal expansion closer to that of the substrate, leading to a better thermal cycle reliability [11]. One important issue with paste sintering in double-side modules is that it requires very precise deposition to fit the different thicknesses between dies, interposers (used to manage the electric field close to the voltage terminations of the chip) and substrates [12]. To overcome that issue, another solution under development is the use of electrodeposited copper nanowires [13]. After the thermocompression process, shear strengths higher than 10 MPa can then be achieved based on the latter technology [14]. While this bonding technique is very promising, it requires the use of a sacrificial membrane.

This paper proposes a preliminary evaluation of a novel attachment technique based on thermocompression of porous electrodeposited copper. Fig. 1 shows an example of what could be achieved using an electro-chemical process: massive copper is first deposited on a substrate to replace the
interposer. Then, by controlling the current density and the acidity of the chemical bath, a 100 µm thick layer of porous copper is deposited on it by a method described later in the paper. This easily deformable porous deposit should allow for better manufacturability of double-side power modules, without the need for a sacrificial membrane.

The next section briefly describes the methodology. Then, various thermocompression parameters are tested and evaluated. Finally, thermal and mechanical characterizations after thermal ageing are proposed, and perspectives are highlighted.

<figure><img src="image_2.png" /><figcaption>Fig. 1. Electrodeposition of massive and porous copper to make power modules with double-side cooling.</figcaption></figure>

## 2. Test samples and characterization tools

### 2.1. Deposition technique of porous films

Porous copper films are deposited on DBC (Direct Bonding Copper) substrates with aluminum nitride (AlN) ceramic. The thicknesses of the different layers are 300 µm for copper and 1 mm for AlN. On each substrate, four diodes (ref. 5SLY 12E1200 – ABB – 6.3mm×6.3mm) are thermocompressed at the same time.

Electrochemical deposition is achieved using the DHBT (Dynamic Hydrogen Bubble Template) technique [15]. Two electrodes are placed in an acid copper bath. By controlling the applied current density, it is possible to achieve a double reduction at the cathode, with both copper ions transforming into metallic copper and $H^+$ ions forming into $H_2$ bubbles. In this way, copper is deposited around the hydrogen bubbles, as presented in Fig. 2a, and the film porosity is formed once they have escaped. By controlling the current flowing between the electrodes, it is possible to generate pores of different, controlled sizes. For instance, Fig. 2b shows top views of various films formed with different current densities. It can be seen that, globally, pore and ligament sizes decrease as current density increases. The microstructure is also

dependent on other parameters such as presence of additives and current modulation (DC current, pulsed current, etc.).

For this work, the deposition conditions are: 300 A/dm² DC current, duration 30s, $CuSO_4$ 0.4 mol/L, $H_2SO_4$ 1.5 mol/L. Note that this current density value is huge compared to classical copper electrodepositions but is required to obtain the double reduction and create the necessary porosity.

<figure><img src="image_3.png" /><figcaption>a. Schematic view [15]</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>b. Top view of DHBT films with different current densities</figcaption></figure>

<caption>Fig. 2. Presentation of the DHBT technique.</caption>

The microstructure of the film, observed by optical microscopy or tomography, is inhomogeneous along its thickness, as presented in Fig. 3. It can be seen in Figs. 3.a and 3.c that pore size is smaller close to the interface with copper metallization of the DBC substrate.
<figure><img src="image_5.png" /><figcaption>a. Porous copper film before thermocompression (cross-section perpendicular to the substrate)</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>b. Diode assembled after thermocompression (cross-section perpendicular to the substrate)</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>c. Tomography cross-sections of a film at different heights before thermocompression (cross-sections parallel to the substrate)</figcaption></figure>

<caption>Fig. 3. Description of porous films before and after thermocompression.</caption>

After deposition, the oxidation layer present on the films is removed in a reducing atmosphere (95% He, 5% H₂) at 500°C prior to the thermocompression step. However, this reduction could also be achieved by using a chemical process.

## 2.2. Thermocompression of porous films

The assembly is placed between the jaws of a thermocompression machine. A schematic diagram of this machine is shown in Fig. 4. The thermocompression parameters are presented in Tab. 1. The process is described hereafter.

The upper jaw is mobile and is first put in contact with the diodes, until a low load is applied (10% of full pressure, provided in Tab. 1). Given the low thickness of the copper films (≈20 µm after thermocompression), the jaws must be parallel to each other so that the load is uniformly distributed across

the 4 diodes. To this end, a ball-and-socket joint is positioned under the lower jaw. The whole assembly is then heated in a dynamic vacuum to prevent oxidation, after purging with hydrogenated argon. Throughout the test, pressure in the thermocompression machine is less than 10⁻¹ mbar. Then, when the required temperature has been reached and stabilized, full pressure is applied for the required time. Fig. 3.b shows a cross-section of the assembly after thermocompression.

<figure><img src="image_8.png" /><figcaption>Fig. 4. Schematic of the thermocompression setup.</figcaption></figure>

In Tab. 1, sample A is the reference. The other samples are fabricated to evaluate the influence of different parameters on the initial performance (the parameter varied in each test is shown in bold and italics).

A sample without porous copper film is also processed: the diodes are directly thermocompressed on the DBC, under the conditions presented in Tab. 1. This sample will be used to analyze the benefit of the porous film electrochemical deposition.

All samples are scanned by acoustic microscopy, and thermally and mechanically tested. These characterizations are detailed in the following paragraphs.

<table><caption>Table 1 Thermocompression parameters for the different samples</caption><thead><tr><th>Sample</th><th>Temperature (°C)</th><th>Duration (min)</th><th>Pressure (MPa)</th></tr></thead><tbody><tr><td>A (ref.)</td><td>300</td><td>30</td><td>20</td></tr><tr><td>B</td><td><strong>250</strong></td><td>30</td><td>20</td></tr><tr><td>C</td><td><strong>350</strong></td><td>30</td><td>20</td></tr><tr><td>D</td><td>300</td><td><strong>15</strong></td><td>20</td></tr><tr><td>E</td><td>300</td><td><strong>60</strong></td><td>20</td></tr><tr><td>F</td><td>300</td><td>30</td><td><strong>10</strong></td></tr><tr><td>G</td><td>300</td><td>30</td><td><strong>30</strong></td></tr></tbody></table>

## 2.3. Characterization tools

In order to analyze the quality of the physical contact between the substrates and the dies, Scanning
Acoustic Microscopy (SAM) images of the four diodes are obtained. This method will reveal any inhomogeneity in the contact surface and determine if delamination is present after thermocompression.

Then, to compare the different process parameters, thermal characterization of the attachment between diodes and substrates is carried out by injecting a high current (80 A) into the diodes for a short time (15 ms) and measuring the resulting junction temperature rise. This junction temperature is obtained by measuring the thermo-sensitive electrical parameter $V_f$ (threshold voltage of the diode under 10 mA current). The test is carried out using the Phase 12B thermal analyzer (Analysis Tech). Pulse duration was determined by the help of thermal simulations, which are not presented in this paper. A sample prepared for thermal characterization is shown in Fig. 5.

Eventually, shear strength tests are carried out on three of the four diodes for each sample with a Royce 600 machine. The head tool is positioned 20 µm above the substrate surface, while the displacement rate is fixed at 1mm/min. The last diode is used for microstructural analysis.

<figure><img src="image_9.png" /><figcaption>Fig. 5. Sample with 4 diodes before thermal characterization.</figcaption></figure>

# 3. Characterization results after fabrication

## 3.1. Preliminary characterizations

To analyze the effectiveness of the deposit of a porous film, Fig. 6 compares the SAM images of a thermocompressed assembly made with a porous film (sample A) and another made without any film. A dark SAM image corresponds to a densified zone and a delamination is characterized by a clearer area. Concerning the sample without film (blank sample), the image analysis shows that at least 60% of the contact is delaminated. This demonstrates the interest of the porous copper film on the surfaces to create an acceptable physical contact.

## 3.2. Effects of thermocompression parameters

Homogeneity of thermocompression on each substrate is confirmed by the thermal and mechanical test results shown in Fig. 7 and Fig. 8, respectively.

While some disparities can be observed between diodes of the same sample, the differences remain relatively low. Shear strength values higher than 25 MPa are obtained with the best thermocompression condition (300 °C, 30 minutes, 30 MPa), which corresponds to the lowest thermal impedance value.

<figure><img src="image_10.png" /><figcaption>Fig. 6. SAM observations after thermocompression.</figcaption></figure>

Figs. 7 and 8 are also useful to evaluate the impact of the main processing parameters on joint quality. Influence of temperature can be observed with the results of samples A (300°C), B (250°C) and C (350°C). Logically, thermal tests show a decrease in average thermal impedance, with a difference of less than 0.02 K/W. On the contrary, temperature greatly influences shear strength. However, at 350°C, dies could be damaged during the process. Samples A (30 minutes), D (15 minutes), and E (60 minutes) are used to evaluate the impact of thermocompression duration. While thermal tests do not yield decisive results, shear tests show a clear improvement, even if shear strength remains lower than 10 MPa with the chosen parameters. Finally, influence of pressure is assessed with samples A (20 MPa), F (10 MPa), and G (30 MPa). As expected, thermal and shear test results are better when this parameter is increased. Differences higher than 0.02 K/W are observed in the thermal tests. Shear strength is highly dependent on this parameter, with the best result close to 25 MPa in acceptable conditions for the dies.

Also, a sample with the Au-Sn solder was fabricated to make a comparison with the thermocompressed films. The average measured thermal impedance at 15 ms is 0.27 K/W, while shear strength is above 50 MPa.

To conclude, this section shows that thermocompression of porous electrodeposited films is effective to make die attachments. Thermal performance is better than that of the Au-Sn solder, but maximum shear strength remains lower irrespective of the fabrication parameters. Anyway, it appears necessary to apply a high pressure (> 30 MPa) since temperature is limited when attaching power semiconductor devices.

Since the joint is made with copper, ageing tests are necessary to evaluate the impact of oxidation
during high temperature storage. Thus, to complete the characterization work, the next section will deal with the ageing of die attachments made using this technique.

<figure><img src="image_11.png" /><figcaption>Fig. 7. Thermal test results – thermal impedance at 15 ms for each diode is marked by a black square, while the average value for each sample is given by a red line – for samples B to G, the figure only gives the modified parameters compared to the reference.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 8. Mechanical test results – the maximum shear strength for each diode is marked by a black square, while the average value for each sample is given by a red line – for samples B to G, the figure only gives the modified parameters compared to the reference.</figcaption></figure>

## 4. Ageing tests

For these tests, DHBT films were thermocompressed with the following parameters: 30°C - 30 minutes - 30MPa. Indeed, compared to the reference parameters of Tab. 1, pressure was increased to obtain a higher shear strength. First, thermal ageing was carried out in air at 200°C, then, in a second phase, tests were carried out under conditions closer to real applications, with the presence of dielectric gel around the chips. Finally, preliminary thermal cycling ageing tests were also carried out.

### 4.1. Thermal ageing in air

For these tests, 4 samples are placed in an oven with air at 200°C. Their performance is compared with that of the pristine sample. The first aged sample is removed from the oven after 200 h, and the others after 500 h, 700 h, and 1000 h, respectively. Each sample with 4 diodes is used for thermal impedance

measurements and shear strength tests. Shear tests are carried out on 3 diodes only, as one of the diodes is used for microscope observation. It should be noted that the tests are carried out on different chips each time, as the shear test is destructive.

Fig. 9 shows thermal impedance as a function of ageing time. Impedance increases before 200 h then stabilizes for subsequent measurements. Fig. 10, on the other hand, shows an almost stable shear strength value.

<figure><img src="image_13.png" /><figcaption>Fig. 9. Thermal test results after thermal ageing at 200°C in air. The average value for each sample is given by a red line.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 10. Mechanical test results after thermal ageing at 200°C in air. The average value for each sample is given by a red line.</figcaption></figure>

To understand thermal behavior after ageing, optical microscope measurements are carried out. The results are shown in Fig. 11. Appearance of oxide can be seen clearly at 200 h, which may explain the observed degradation in thermal performance. It can also be seen that oxidation is not homogeneous throughout the joint. This could account for the lack of change in shear strength: the joint would densify under the effect of temperature in certain zones, which would compensate for the degradation due to the appearance of oxide in other zones.
<figure><img src="image_15.png" /><figcaption>Fig. 11. Oxide appearance after ageing in air.</figcaption></figure>

Accordingly, oxidation of the copper joint is not detrimental from a mechanical point of view. This is consistent with other research results on sintered copper pastes, where the mechanical strength of the joint was increased during the first 100 thermal shock cycles and was maintained for 1000 cycles. The Cu₂O filled up the joint pores and densified the Cu joint, resulting in strengthening during the testing period [16].

Thus, copper oxidation appears to have a detrimental effect on the thermal properties of die

attachments. However, in a real application, components are encapsulated in insulating gel, which changes the conditions observed by the components as they age. It is therefore interesting to carry out ageing under dielectric gel to observe its effect.

## 4.2. Thermal ageing in dielectric gel at 200°C

Samples are fabricated to study the ageing of encapsulated components. The silicone gel is SYLGARD 527. For these tests, only one sample is characterized, so shear strength measurements are not possible. The sample is thus returned to the oven after each thermal impedance measurement. This makes it possible to follow the evolution of the thermal impedance of each diode as a function of time. Fig. 12 shows no clear trend, leading to conclude that ageing has no impact on thermal performance and that oxidation is negligible in this case.

<figure><img src="image_16.png" /><figcaption>Fig. 12. Thermal test results after thermal ageing (200°C) in dielectric gel. The average value for each sample is given by a red line.</figcaption></figure>

## 4.3. Thermal cycling

To conclude, thermal cycling tests are carried out under the following conditions:

- atmosphere: air,

- minimum temperature: -55°C

- maximum temperature: +175°C

- duration time at minimum and maximum temperatures: 10 min

- ramps: +/- 10°C/min.

Samples are fabricated on AMB (Active Metal Brazing) substrates with Si₃N₄, which are more resistant to thermal cycling than AlN-based DBC substrates. The results are shown in Figs. 13, 14 and 15. Fig. 13 shows that thermal impedance would appear to increase, but less quickly than in the case of ageing at 200°C in air. The oxidation phenomenon must be less significant in this case because temperature is globally lower. Fig. 14 shows that shear strength does not vary significantly during thermal cycling as in the case of thermal ageing. To confirm that, SAM images are presented in Fig. 15. It can be seen that no delamination is observed after 500h.
<figure><img src="image_17.png" /><figcaption>Fig. 13. Thermal test results after thermal cycling in air. The average value for each sample is given by a red line.</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>Fig. 14. Mechanical test results after thermal cycling in air. The average value for each sample is given by a red line.</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>Fig. 15. SAM images before and after thermal cycling in air.</figcaption></figure>

With these preliminary results, it seems that behavior of the joint under thermal cycling is good but that this should be confirmed by complementary tests of a longer duration.

## 5. Conclusion

This paper shows that the combination of the Dynamic Hydrogen Bubble Template (DHBT) and thermocompression methods allows the creation of effective die attachments. From a thermal point of view, it is difficult to compare the results with the literature since thermal impedance strongly depends on substrate properties. However, thermal impedance of the same assembly with an Au-Sn solder was evaluated, and a higher thermal impedance (≈0.27 K/W) was obtained, thus demonstrating the good thermal behavior of this novel attachment technique.

From the shear strength point of view, our process provides acceptable results for power electronics,

with thermocompression pressures higher than 20 MPa. However, the attachment remains weaker than that obtained by silver or copper paste sintering, even with far higher temperatures, pressures and durations during thermocompression. This is probably due to coarser microstructure in the porous film compared to that in sintered copper pastes.

Behavior of this attachment method after thermal ageing at 200°C under air was also evaluated. A slight thermal impedance increase was observed during the first 200 hours due to oxidation, followed by stabilization. Hence, thermal ageing tests under silicone gel were carried out to analyze the impact of the atmosphere. They showed that degradation ceased to occur in these conditions. Moreover, after 500 large amplitude thermal cycles, no delamination was detected in the joint, and the thermal and mechanical properties were only slightly affected.

In the future, many parameters must be tested to further improve joint quality, notably process parameters during porous film deposition (current shape, chemical additives, etc.). In fact, these parameters have a significant influence on the microstructure of the film and therefore on its densification during thermocompression. Other thermocompression parameters (atmosphere, surface nature, etc.) must also be studied. Furthermore, it will be important to analyze in more detail the thermocompression process. For instance, can electrodeposited copper films be easily deformed or are they more likely to break due to their brittleness? This is one of the numerous questions that should be answered in the interest of future research.

## Acknowledgements

The authors would like to thank the ANR agency for the financial support of the CopperPack (ANR-19-CE05-0011) project.

## References

[1] T. Y. Hung, S. Y. Chiang, C. J. Huang, C. C. Lee, et al., "Thermal-mechanical behavior of the bonding wire for a power module subjected to the power cycling test", *Microelectronics Reliability*, vol. 51, n° 9, p. 1819-1823.

[2] M. Ciappa, "Selected failure mechanisms of modern power modules," *Microelectronics reliability*, vol. 42, n°4-5, pp. 653-667, 2002.

[3] K. Xing, F. C. Lee, et al., "Extraction of parasitics within wire-bond IGBT modules", in *APEC '98 Thirteenth Annual Applied Power Electronics Conference and Exposition*, Anaheim, CA, USA: IEEE, 1998.

[4] C. Gillot, C. Schaeffer, C. Massit, et al., "Double-sided cooling for high power IGBT modules
using flip chip technology », *IEEE Transactions on Components and Packaging Technologies*, vol. 24, no 4, p. 698-704, dec. 2001.

[5] Liu, M., Coppola, A., Alvi, M., & Anwar, M. (2022). Comprehensive review and state of development of double-sided cooled package technology for automotive power modules. *IEEE Open Journal of Power Electronics*, 3, 271-289.

[6] M. Wang et al., « Reliability Improvement of a Double-Sided IGBT Module by Lowering Stress Gradient Using Molybdenum Buffers », IEEE J. Emerg. Sel. Topics Power Electron., vol. 7, no 3, p. 1637-1648, sept. 2019.

[7] H. Zhang et al., “Failure analysis and reliability evaluation of silver-sintered die attachment for high-temperature applications”, *Microelectronics Reliability*, vol. 94, pp. 46-55, 2019.

[8] Y. Liu, H. Zhang, L. Wang, X. Fan, G. Zhang, et F. Sun, « Effect of Sintering Pressure on the Porosity and the Shear Strength of the Pressure-Assisted Silver Sintering Bonding », *IEEE Transactions on Device and Materials Reliability*, vol. 18, no 2, p. 240-246, juin 2018.

[9] A. Leader, G. Gaustad, C. Babbitt, “The effect of critical material prices on the competitiveness of clean energy technologies,” *Mater Renew Sustain Energy*, vol. 8, n°2, p. 8, 2019.

[10] R. Khazaka et al., “Survey of High-Temperature Reliability of Power Electronics Packaging Components,” *IEEE Trans. Power Electron.*, vol. 30, no 5, p. 2456-2464, 2015.

[11] T. Furukawa et al., "High power density side-gate HiGT modules with sintered Cu having superior high-temperature reliability to sintered Ag," 2017 29th International Symposium on Power Semiconductor Devices and IC's (ISPSD), Sapporo, Japan, 2017, pp. 263-266.

[12] C. Ding, H. Liu, K. D. T. Ngo, R. Burgos, et G.-Q. Lu, « A Double-Side Cooled SiC MOSFET Power Module With Sintered-Silver Interposers: I-Design, Simulation, Fabrication, and Performance Characterization », IEEE Trans. Power Electron., vol. 36, no 10, p. 11672-11680, oct. 2021.

[13] V. Nguyen et al.; “Fabrication of bottom die substrate solderless interconnection based on nano copper wires,” 13th European Conference on Power Electronics and Applications, p. 1-9, sept. 2009.

[14] Z. Yu et al., “Cu-Cu Thermocompression Bonding with Cu-Nanowire Films for Power Semiconductor Die-Attach on DBC Substrates,” *IEEE 23rd Electronics Packaging Technology Conference (EPTC)*, déc. 2021.

[15] Y. Li et al., “Hydrogen bubble dynamic template synthesis of porous gold for nonenzymatic electrochemical detection of glucose,” *Electrochem. Commun.*, vol. 9, no 5, p. 981-988, may 2007.

[16] Y. Gao et al., “Reliability analysis of sintered Cu joints for SiC power devices under thermal shock condition,” *Microelectronics Reliability*, vol. 100-101, 2019.