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. 2025 Jul 25;17(15):2034.
doi: 10.3390/polym17152034.

Hygrothermal Stress Analysis of Epoxy Molding Compound in Fan-Out Panel-Level Package Based on Experimental Characterization and Structural Sensitivity

Yu-Chi Sung  1 , Chih-Ping Hu  1 , Sheng-Jye Hwang  1 , Ming-Hsien Shih  2 , Wen-Hsiang Liao  3 , Yong-Jie Zeng  3 , Cheng-Tse Tsai  4
Affiliations

Hygrothermal Stress Analysis of Epoxy Molding Compound in Fan-Out Panel-Level Package Based on Experimental Characterization and Structural Sensitivity

Yu-Chi Sung et al. Polymers (Basel). .

Abstract

As semiconductor devices demand higher input-output density and faster signal transmission, fan-out panel-level packaging has emerged as a promising solution for next-generation electronic systems. However, the hygroscopic nature of epoxy molding compounds raises critical reliability concerns under high-temperature and high-humidity conditions. This study investigates the hygrothermal stress of a single fan-out panel-level package unit through experimental characterization and numerical simulation. Thermal-mechanical analysis was conducted at 100 °C and 260 °C to evaluate the strain behavior of two commercial epoxy molding compounds in granule form after moisture saturation. The coefficient of moisture expansion was calculated by correlating strain variation with moisture uptake obtained under 85 °C and 85% relative humidity, corresponding to moisture sensitivity level 1 conditions. These values were directly considered into a moisture -thermal coupled finite element analysis. The simulation results under reflow conditions demonstrate accurate principal stress and failure location predictions, with stress concentrations primarily observed at the die corners. The results confirm that thermal effects influence stress development more than moisture effects. Finally, a structural sensitivity analysis of the single-package configuration showed that optimizing the thickness of the dies and epoxy molding compound can reduce maximum principal stress by up to 12.4%, providing design insights for improving package-level reliability.

Keywords: fan-out panel-level packaging; hygrothermal stress; moisture effect; reliability; structural sensitivity analysis.

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Conflict of interest statement

Authors Wen-Hsiang Liao and Yong-Jie Zeng were employed in Packaging Product Simulation and Design, Innolux Corporation, Tainan, Taiwan; author Cheng-Tse Tsai was employed at the Testing Center, Innolux Corporation, Tainan, Taiwan. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Process flowchart of molding-first and RDL-first fan-out process.
Figure 2
Figure 2
Schematic of moisture experiment procedures.
Figure 3
Figure 3
Schematic of thermal–mechanical analyzer (Q400 TMA).
Figure 4
Figure 4
Schematic of TMA experiment procedures.
Figure 5
Figure 5
Location of EMC and fixture in TMA.
Figure 6
Figure 6
Different testing conditions for TMA experiments.
Figure 7
Figure 7
(a) The strain variation at different testing conditions. (b) The strain variation with the two EMC materials.
Figure 8
Figure 8
Calculation procedure for coefficient of moisture expansion.
Figure 9
Figure 9
Coefficient of moisture expansion at different temperatures.
Figure 10
Figure 10
Analysis procedures of hygrothermal stress analysis.
Figure 11
Figure 11
Top view of single-package model.
Figure 12
Figure 12
Schematic of sectional view of quarter single-package model.
Figure 13
Figure 13
Temperature profile setting of MSL 1 testing conditions.
Figure 14
Figure 14
Initial concentration setting of package model.
Figure 15
Figure 15
Concentration setting during moisture diffusion process.
Figure 16
Figure 16
Moisture concentration results with different mesh sizes.
Figure 17
Figure 17
Moisture concentration results with different time steps.
Figure 18
Figure 18
Maximum principal stress results with different mesh sizes.
Figure 19
Figure 19
Interpretation method of maximum principal stress results.
Figure 20
Figure 20
Moisture diffusion results under MSL 1 testing conditions.
Figure 21
Figure 21
Thermal stress induced by temperature effect.
Figure 22
Figure 22
Moisture stress induced by humidity effect.
Figure 23
Figure 23
Hygrothermal stress induced by temperature and humidity effects.
Figure 24
Figure 24
Equivalent expansion coefficient at different temperatures.
Figure 25
Figure 25
Principal stress distribution induced by thermal effect under reflow conditions.
Figure 26
Figure 26
Principal stress distribution induced by thermal–moisture–vapor effects under reflow conditions.
Figure 27
Figure 27
Maximum stress distribution of (a) von-Mises stress and (b) maximum shear stress between die and EMC.
Figure 28
Figure 28
Cross-section schematic of single package.
Figure 29
Figure 29
Maximum stress value results from seven cases.
Figure 30
Figure 30
Maximum principal stress values with different die and overmold thicknesses.
Figure 31
Figure 31
Schematic of stress value locations.
Figure 32
Figure 32
Sensitivity analysis results.
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