Diffusion behavior of Cu in Cu/electroless Ni and Cu/electroless Ni/Sn-37Pb solder joints in flip chip technology

2006 ◽  
Vol 35 (12) ◽  
pp. 2164-2171 ◽  
Author(s):  
Yu-Ching Hsu ◽  
Jenq-Gong Duh
Keyword(s):  
Flip Chip ◽  
Solder Joints ◽  
Diffusion Behavior ◽  
Chip Technology ◽  
Electroless Ni

High Productivity Thermo-Compression Flip Chip Bonding

2014 ◽  
Vol 2014 (1) ◽  
pp. 000100-000106
Author(s):  
Tom Colosimo ◽  
Horst Clauberg ◽  
Evan Galipeau ◽  
Matthew B. Wasserman ◽  
Michael Schmidt-Lange ◽  
...  
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Flip Chip ◽  
Solder Joints ◽  
Rapid Heating ◽  
Temperature Cycle ◽  
Temperature Uniformity ◽  
Heating Rates ◽  
Heating And Cooling ◽  
Chip Technology

Advancements in electronic packaging performance and cost have historically been driven by higher integration primarily provided by fab shrinks that has followed the well-known Moore's law. However, due to the tremendous and continuously increasing cost of building new fabs, the performance/cost improvements achieved via node shrinks are negated. This leaves packaging innovation as the vehicle to achieve future cost-performance improvements. This has initiated a More-than-Moore idea that has led to vigorous R&D in packaging. Advanced packages which employ ultra-fine pitch flip chip technology for chip-to-substrate, chip-to-chip, or chip-to-interposer for the first level interconnect have been developed as an answer to obtaining higher performance. However, the costs are too high as compared to traditional wire bonding. The status today is that the fundamental technical hurdles of manufacturing the new advanced packages have been solved, but cost reduction and yield improvements have to be addressed for large-scale adoption into high volume manufacturing. In traditional flip chip assembly silicon chips are tacked onto a substrate and then the solder joints are melted and mass reflowed in an oven. This mass reflow technique is troublesome as the pitch of the solder bumps become finer. This is due to the large differences in the thermal expansion coefficient of the die and the substrate, which creates stress at the solder joints and warpage of the package when the die and substrate are heated and cooled together. To mitigate and resolve this issue, thermo-compression bonders have been developed which locally reflow the solder without subjecting the entire substrate to the heating and cooling cycle. This requires that the bondhead undergo heating past the melting point of solder and then cooling down to a low enough temperature to pick the next die from the wafer that is mounted to tape. Machines in the market today can accomplish this temperature cycle in 7 to 15 seconds. This is substantially slower than the standard flip chip process which leads to high cost and is delaying the introduction of these new packages. This paper shows a flip chip bonder with a new heating and cooling concept that will radically improve the productivity of thermo-compression bonding. Data and productivity cycles from this new bond head with heating rates of over 200°C/sec and cooling of faster than 100°C/sec are revealed. Experimental results are shown of exceptional temperature accuracy across the die of 5°C throughout the cycle and better than 3°C at the final heating stage. The high speed thermo-compression bonds are analyzed and the efficacy of the new concept is proven. Excellent temperature uniformity while heating rapidly is an absolute necessity for enabling good solder joints in a fast process. Without good temperature uniformity, additional dwell times need to be incorporated to allow heat to flow to all of the joints, negating any benefits from rapid heating. Whereas the current state-of-that-art is often to program temperature in steps, this bonder can be commanded and accurately follows more complex temperature profiles with great accuracy. Examples of how this profiling can be used to enhance the uniformity and integrity of the joints with non-conductive pastes, film, and without underfill along with the associated productivity improvements will be shown. Tests that show portability across platforms that will lead to set up time and yield improvements and are identified and quantified. Additionally new ideas for materials and equipment development to further enhance productivity and yield are explored.

Interfacial Morphology and Shear Deformation of Flip Chip Solder Joints

2000 ◽  
Vol 15 (8) ◽  
pp. 1679-1687 ◽  
Author(s):  
J. W. Jang ◽  
C. Y. Liu ◽  
P. G. Kim ◽  
K. N. Tu ◽  
A. K. Mal ◽  
...  
Keyword(s):  
Shear Deformation ◽  
Dielectric Layer ◽  
Flip Chip ◽  
Solder Joints ◽  
Organic Substrate ◽  
Failure Behavior ◽  
Interfacial Morphology ◽  
Solder Interconnects ◽  
Solder Balls ◽  
Electroless Ni

We examined the interfacial morphology and shear deformation of flip chip solder joints on an organic substrate (chip-on-board). The large differences in the coefficients of thermal expansion between the board and the chip resulted in bending of the 1-cm2 chip with a curvature of 57 ± 12 cm. The corner bump pads on the chip registered a relative misalignment of 10 μm with respect to those on the board, resulting in shear deformation of the solder joints. The mechanical properties of these solder joints were tested on samples made by sandwiching two Si chips with electroless Ni(P) as the under-bump metallization and 25 solder interconnects. Joints were sheared to failure. Fracture was found to occur along the solder/Ni3Sn4 interface. In addition, cracking and peeling damages of the SiO2 dielectric layer were observed in the layer around the solder balls, indicating that damage to the dielectric layer may have occurred prior to the fracture of the solder joints due to a large normal stress. The failure behavior of the solder joints is characterized by an approximate stress analysis.

Solder reaction-assisted crystallization of electroless Ni–P under bump metallization in low cost flip chip technology

1999 ◽  
Vol 85 (12) ◽  
pp. 8456-8463 ◽  
Author(s):  
J. W. Jang ◽  
P. G. Kim ◽  
K. N. Tu ◽  
D. R. Frear ◽  
P. Thompson
Keyword(s):  
Flip Chip ◽  
Low Cost ◽  
Under Bump Metallization ◽  
Chip Technology ◽  
Solder Reaction ◽  
Electroless Ni

Predicting the Liquid Formation for the Solder Joints in Flip Chip Technology

2005 ◽  
Vol 128 (4) ◽  
pp. 331-338 ◽  
Author(s):  
Wen-Hwa Chen ◽  
Shu-Ru Lin ◽  
Kuo-Ning Chiang
Keyword(s):  
Surface Tension ◽  
Solder Joint ◽  
Flip Chip ◽  
Solder Joints ◽  
Geometric Method ◽  
External Loading ◽  
Surface Evolver ◽  
Eutectic Solder ◽  
Chip Technology ◽  
Interfacial Surface

An accurate and efficient analytical geometric method is presented for predicting the geometric parameters of the controlled collapse chip connection type solder joint using direct chip attach technology after a reflow process. By this method, the meridian of the solder joint is first discretized as a series of sufficiently fine fragmental arcs. After calculating the internal pressure inside the molten eutectic solder from the forces balance, the meridional and circumferential radii of curvature of each arc are then obtained from the Laplace-Young equation. As a result, the coordinates of each node of the arc and the solder joint geometry can be determined in turn. The factors that affect the final shape of the molten eutectic solder joints, including the solder volumes, external loading, pad size, surface tension of molten eutectic solder, and interfacial surface tension between the molten eutectic solder and the solid high-lead bump are considered herein. The results computed by the analytical geometric method are also compared with those obtained using the Surface Evolver program, the extended Heinrich’s model, and the experimental results. The results of the various approaches are mutually consistent.

Effect of electromigration on mechanical shear behavior of flip chip solder joints

2006 ◽  
Vol 21 (3) ◽  
pp. 698-702 ◽  
Author(s):  
Jae-Woong Nah ◽  
Fei Ren ◽  
Kyung-Wook Paik ◽  
K.N. Tu
Keyword(s):  
Flip Chip ◽  
Shear Failure ◽  
Solder Joints ◽  
Electron Flow ◽  
Shear Behavior ◽  
Cathode Side ◽  
Current Stressing ◽  
Large Growth ◽  
Electroless Ni ◽  
Solder Interface

Effect of electromigration on mechanical shear behavior of flip chip solder joints consisting of 97Pb3Sn and 37Pb63Sn composite solder joints was studied. The under bump metallurgy (UBM) on the chip side was TiW/Cu/electroplated Cu, and the bond pad on the board side was electroless Ni/Au. It was found that the mode of shear failure has changed after electromigration and the mode depends on the direction of electron flow during electromigration. The shear induced fracture occurs in the bulkof 97Pb3Sn solder without current stressing, however, after 10 h current stressing at 2.55 × 104 A/cm2 at 140 °C, it occurs alternately at the cathode interfaces between solder and intermetallic compounds (IMCs). In the downward electron flow, from the chip to substrate, the failure site was at the Cu–Sn IMC/solder interface near the Si chip. However, in the upward electron flow, from the substrate to chip, failure occurred at the Ni–Sn IMC/solder interface near the substrate. The failure mode has a strong correlation to microstructural change in the solder joint. During the electromigration, while Pb atoms moved to the anode side in the same direction as with the electron flow, Sn atoms diffused to the cathode side, opposite the electron flow. In addition, electromigration dissolves and drives Cu or Ni atoms from UBM or bond pad at the cathode side into the solder. These reactions resulted in the large growth of Sn-based IMC at the cathode sides. Therefore, mechanical shear failure occurs predominantly at the cathode interface.

Evaluation of electromigration in flip-chip solder joints

2011 ◽  
Vol 2011 (1) ◽  
pp. 000979-000984 ◽  
Author(s):  
Hyun-Kyu Lee ◽  
Yong-Chul Chu ◽  
Myung-Ho Chun ◽  
Sang-Ho Jeon ◽  
Jung-Ug Kwak ◽  
...  
Keyword(s):  
Electric Current ◽  
Flip Chip ◽  
Solder Joints ◽  
Cathode Side ◽  
Time To Failure ◽  
Chip Technology ◽  
Solder Bumps ◽  
Solder Balls ◽  
Initial Resistance ◽  
Reliability Issue

The flip-chip solder joint has become one of the most important technologies of high-density packaging in the microelectronics industry. But, electromigration has become a critical reliability issue in flip-chip technology. Because the dimensions of solder joints are expected to decrease and current density is expected to increase. This study is about electromigration of flip-chip solder joints, we evaluated many kinds of solder balls such as SnAgCu, SnCu and so on in flip chip package. The lifetime against electromigration was defined the fail from the value of resistance with electric current reaches 1.5 times of that of initial resistance with electric current for. In solder bumps with electric current, since the atoms composed of the solder bump and UBM move in the direction of electron flows, the IMC was accumulated on the anode side. Meanwhile, the IMC disappeared in the cathode side, and the voids were formed. In the solder bumps without electric current, the IMC gradually grew on both sides. SnAgCu had better lifetime than SnCu, and different time-to-failure caused by different crystallographic orientation of Sn. And various dopants in SnCu had a different EM lifetime each other.

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