Empirical Equations for Optimization Conditions in Thermal Compression Bonding of Copper Pillar Flip Chip Packages

Wu, Mei-Ling; Chiou, S. J.; Hwang, Yeong‐Maw

doi:10.1109/tcpmt.2018.2821443

Cited by 4 publications

(3 citation statements)

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“…Once the spring constant is obtained, the analytical model (7) for the harmonic motion of a misaligned chip during reflow is used to evaluate the self-alignment response of the reflowed chips. The value of the damping ratio, 𝜁 = 1 𝜔 0 𝜏 0 (15) for both the 320×256 and 640×512 FPAs is less than 1. This is a criterion for having oscillatory motion with amplitude which is gradually decreasing to 0, meaning self-alignment is taking place.…”

Section: Take Fig 14mentioning

confidence: 85%

“…Computational modeling of assembly processes has been used previously to assess and predict the formation of solder joints and other interconnects of electronic components. For example, Wu et al studied the deformation mechanisms of a single bump configuration that includes a copper pillar, a solder ball, and a copper to assess the thermal compression process parameters that affect the bonding results [15]. A finite element model of the bonding forming for 3-D flip-chip stacked gold stud bumps was developed to simulate the effect of the controlled bonding conditions [18].…”

Section: Introductionmentioning

confidence: 99%

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Modeling Insights Into the Assembly Challenges of Focal Plane Arrays

Stoyanov

Bailey

2023

IEEE Access

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Ongoing technological advances in photodetector material growth and processing, readout integrated circuits, and robust hybridization (packaging) methods for assembling high-resolution and smallpitch size pixel arrays are the main enabling factors for pushing the frontiers of high-performance Focal Plane Array (FPA) technologies for imaging systems. This paper details the development of analytical and numerical models and demonstrates their use to generate insights into the feasibility of two flip-chip assembly processes for packaging infrared (IR) detector chips. The modelling studies focus on the challenges of forming the indium interconnection arrays in the case of the FPA technologies using Group III-V compound semiconductor materials and ultra-fine pitch pixel array layouts. The accurate alignment of the IR detector chip onto the readout chip in the case of high-density pixel architectures is a critical requirement for the packaging process. To gain better understanding of this requirement, which has a clear implication for the quality and subsequent reliability performance of the FPA, compression and reflow bonding process models are developed using suitable modeling approaches and methods and then demonstrated for two distinctive focal plane array design configurations. The novelty of this work is in the developed modeling capabilities utilizing different computational methods, from large deformation and contact analysis finite element to energy-based and harmonic motion mechanics, to characterize and optimize the mechanical and dynamic non-linear behavior of the indium solder joints and their formation during FPA packaging. The feasibility of bonding techniques for different resolution FPAs and under flip-chip misalignment conditions is assessed. The modeling results pointed to a very strict, sub-micrometer flip-chip placement accuracy requirement for the assembly of FPAs with ultra-fine indium bump array resolution.INDEX TERMS IR detectors, Focal Plane Array, compression bonding simulation, reflow self-alignment modeling, indium joints, ultra-fine pitch flip chip assembly, compound semiconductors.

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Section: Take Fig 14mentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Modeling Insights Into the Assembly Challenges of Focal Plane Arrays

Stoyanov

Bailey

2023

IEEE Access

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“…In terms of materials, a copper pillar [41] and a copper ball [42]- [44] are ideal candidates for the vertical transition. Reference [41] analyzed the plastic deformation of a copper pillar in flip-chip package using finite element method, and demonstrated its more stable characteristic impedance (compared to the copper ball) due to its cylindrical geometry. Nevertheless, it was easier to handle the copper ball (than the copper pillar) because the direction or angle was no longer required for such.…”

Section: Introductionmentioning

confidence: 99%

Experimental Verification of Excavated Structure on Multi-Layered Substrates for Millimeter-Wave Signal Vertical Transition Using Copper Balls

Yoshida

Nishikawa

2020

IEEE Access

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This paper presents a vertical transition of millimeter-wave signal for interconnection between multi-layered substrates, which utilizes copper balls for vertical interconnection, as both for electrical connection and physical support. In particular, the copper balls were used to configure a quasi-coaxial transmission line at the vertical interconnection. The key idea was to create an excavated structure at the location of the copper balls to fix it, given that the copper balls slightly fluctuate during reflow soldering when simply placed on a flat surface. Such activity of the copper balls defines large variation in transmission characteristics at millimeter-wave band that produce low yield rate. Practically, with the proposed method of an excavated structure, the location error of the copper balls can be minimized, leading to high reproducibility in determining the copper balls location, and small variation of the transmission characteristics. To verify the method's effectiveness, a prototype having three vertically stacked multi-layered substrates with the excavated structure was fabricated. The excavation had a depth of 90 µm and diameter of 0.45 mm. The copper balls used had a 0.3-mm diameter. Five samples were fabricated and then evaluated by X-ray images and S-parameter measurements. Based on the results, the reflection characteristics of the measurement were less than −10 dB from dc to 97 GHz in the best-case scenario, whereas the variation in the S-parameters was comparatively small up to 70 GHz. Moreover, the X-ray images showed relatively small copper balls location error. These results indicate that the proposed excavated structure is effective for millimeter-wave vertical interconnections using copper balls, in small wireless terminal applications.

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