Silver Flip-Chip Technology by Solid-State Bonding

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Pin J. Wang ◽  
Chin C. Lee
Keyword(s):  
Solid State ◽  
Flip Chip ◽  
New Technology ◽  
Bonding Process ◽  
Cu Substrate ◽  
Solid State Bonding ◽  
Chip Technology ◽  
Cu Substrates ◽  
One Step ◽  
Lead Free Solders

Silver flip-chip joints between silicon (Si) chips and copper (Cu) substrates were fabricated using a solid-state bonding process without any solder and without flux. The bonding process was performed at 250°C, compatible with typical reflow temperature for lead-free solders. During the bonding process, there was no molten phase involved. The Ag joints fabricated consisted of only pure Ag without any intermetallic compound (IMC). Thus, reliability issues associated with IMCs and IMC growth do not exist anymore. Silver has the highest electrical conductivity and highest thermal conductivity among all metals. It is also quite ductile and able to deform to release stresses caused by thermal expansion mismatch. Flip-chip joints of high aspect ratio can be accomplished because the joints stay in a solid state during the bonding process. It looks like that silver is the ultimate joining material for flip-chip as well as through-Si-via interconnect technologies. In this study, the solid-state bonding process was first developed using a pure Ag foil to bond a Si chip to a Cu substrate in one step. The bonding strength on two interfaces, Si/Ag and Ag/Cu, passes the MIL-STD-883G Method 2019.7. To demonstrate Ag flip-chip interconnects, Si chips were electroplated with Ag bumps, followed by the solid-state bonding process on Cu substrates. The flip-chip bumps are well bonded to the Cu substrate. It would take some time for this new technology to be probably accepted and utilized in production. On the other hand, the preliminary results in this study show that Ag flip-chip joints can indeed be fabricated at 250°C.

40 μm Silver Flip-Chip Interconnect Technology With Solid-State Bonding

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Chu-Hsuan Sha ◽  
Chin C. Lee
Keyword(s):  
Flip Chip ◽  
Bonding Process ◽  
Thermal Expansion Mismatch ◽  
Pure Silver ◽  
Bonding Pressure ◽  
Cu Substrate ◽  
Solid State Bonding ◽  
Cu Substrates ◽  
Lead Free Solders ◽  
Interconnect Technology

Formation of pure silver (Ag) flip-chip interconnect of silicon (Si) chips on copper (Cu) substrates is reported. Arrays of Ag columns, each 36 μm in height and 40 μm in diameter, are fabricated on 2-in. Si wafers which are first coated with chromium (Cr)/gold (Au) dual layers. The Si wafers are diced into 6 mm × 6 mm chips, each having 50 × 50 Ag columns. The Si chip with Ag columns is directly bonded to Cu substrate at 260 °C in 80 mTorr vacuum to inhibit oxidation. The static bonding pressure is as low as 680 psi (4.69 MPa), corresponding to a load of 0.021 oz (0.60 g) per column. During bonding, the Ag columns deform and conform to the Cu substrate. They are well bonded to the Cu. No molten phase is involved in the bonding process. The joints consist of pure Ag only. The ductile Ag joints are able to accommodate the thermal expansion mismatch between Si and Cu. It is well known that in nearly all soldering processes used in electronic industries, intermetallic compound (IMC) formation is essential to make a solder joint. In the pure Ag interconnect, no IMCs exist. Thus, reliability issues associated with IMCs are eliminated. Compared to tin-based lead-free solders, pure Ag joints have superior electrical and thermal properties.

40 μm Copper–Silver Composite Flip-Chip Interconnect Technology Using Solid-State Bonding

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Chu-Hsuan Sha ◽  
Wen P. Lin ◽  
Chin C. Lee
Keyword(s):  
Solid State ◽  
Flip Chip ◽  
Thermal Expansion Mismatch ◽  
Conduction Electrons ◽  
Solid State Bonding ◽  
Cu Substrates ◽  
Atomic Distance ◽  
Free Solder ◽  
Interconnect Technology ◽  
Silver Composite

Copper–silver (Cu–Ag) composite flip-chip interconnect between silicon (Si) chips and Cu substrates is demonstrated. Array of Cu–Ag columns, each 28 μm in height and 40 μm in diameter, is electroplated on 2-in. Si wafers coated with chromium (Cr)/gold (Au) dual layer. The Si wafers are diced into 6 mm × 6 mm chips, each containing 50 × 50 Cu–Ag columns. The Si chip with Cu–Ag columns is bonded to Cu substrates at 260 °C in 80 mTorr vacuum. A bonding force of only 1.8 kg is applied, corresponding to 0.71 g per Cu–Ag column. During bonding, Ag atoms in Cu–Ag columns deform and their surfaces conform to and mate with the surface of Cu substrate. Solid-state bonding incurs when Ag atoms in Cu–Ag columns and Cu atoms in Cu substrates are brought within atomic distance so that they share conduction electrons. The Cu–Ag columns are indeed bonded to the Cu. No molten phase is involved in the bonding. The joint consists of 60% Cu section and 40% Ag section. The ductile Ag is able to accommodate the thermal expansion mismatch between Si and Cu. The Cu–Ag joints do not contain any intermetallic compound (IMC). This interconnect technology avoids all reliability issues associated with IMC growth in conventional soldering processes. Compared to tin-based lead-free solder joints, Cu–Ag composite joints have superior electrical and thermal properties.

40 μm Ag/Au Flip-Chip Joints by Solid-State Bonding at 200°C

2013 ◽  
Vol 10 (3) ◽  
pp. 120-127
Author(s):  
Wen P. Lin ◽  
Chu-Hsuan Sha ◽  
Chin C. Lee
Keyword(s):  
Solid State ◽  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Bonding Interface ◽  
Breaking Force ◽  
Sem Images ◽  
Cross Sectional ◽  
Cu Substrate ◽  
Solid State Bonding ◽  
State Process

In this research, 40 μm silver/gold (Ag/Au) composite flip-chip interconnect joints between silicon (Si) chips and copper (Cu) substrates were demonstrated. The bonding was achieved by a solid-state process at a low temperature of 200°C for 5 min with the pressure applied at 250–400 psi (1.7–2.7 MPa), corresponding to 0.22–0.35 g of force per joint. To begin with, an array of 50 × 50 30 μm Ag/10 μm Au columns with 40 μm in diameter and 100 μm in pitch was fabricated by photolitho-graphic and electroplating processes on silicon (Si) chips which were first coated with chromium (Cr) and Au films. The columns on the chip were then bonded to a Cu substrate by solid-state bonding. Cross-sectional scanning electron microscopy (SEM) images show that the exposed Ag/Au columns were well bonded to the Cu substrate. No joint breakage was observed despite the large coefficient of thermal expansion (CTE) mismatch between Si and Cu. A pull test was conducted. The breaking force and fracture strength are 6.5–7.3 kg and 2,940–3,310 psi (20.2–22.8 MPa), respectively. The breaking force is 2.5× of the criterion specified in MIL-STD-883E. Fracture modes were examined. Three modes were classified by fracture interfaces as Si-glue, Si/Cr/Au/Ag, and Au-Cu bonding interface. Of all joints evaluated, 27% of them break on the Au-Cu substrate bonding interface. Accordingly, the bonding interface is least likely to break among interfaces of the joint structure.

Fe/Ni diffusion behavior in the shear-extrusion solid state bonding process

2021 ◽  
Vol 67 ◽  
pp. 35-45
Author(s):  
Shuangjie Zhang ◽  
Wei Wang ◽  
Shibo Ma ◽  
Qiang Li
Keyword(s):  
Solid State ◽  
Bonding Process ◽  
Diffusion Behavior ◽  
Solid State Bonding

Solder Joint Reliability of Sn-Cu and Sn-Ag-Cu Lead-Free Solder Alloys Solidified on Copper Substrates with Different Surface Roughnesses

2015 ◽  
Vol 830-831 ◽  
pp. 265-269
Author(s):  
Satyanarayan ◽  
K.N. Prabhu
Keyword(s):  
Solder Joint ◽  
Solder Matrix ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Alloys ◽  
Cu Substrate ◽  
Cu Substrates ◽  
Free Solder ◽  
Substrate Surfaces ◽  
Lead Free Solders

In the present work, the bond strength of Sn-0.7Cu, Sn-0.3Ag-0.7Cu, Sn-2.5Ag-0.5Cu and Sn-3Ag-0.5Cu lead free solders solidified on Cu substrates was experimentally determined. The bond shear test was used to assess the integrity of Sn–Cu and Sn–Ag–Cu lead-free solder alloy drops solidified on smooth and rough Cu substrate surfaces. The increase in the surface roughness of Cu substrates improved the wettability of solders. The wettability was not affected by the Ag content of solders. Solder bonds on smooth surfaces yielded higher shear strength compared to rough surfaces. Fractured surfaces revealed the occurrence of ductile mode of failure on smooth Cu surfaces and a transition ridge on rough Cu surfaces. Though rough Cu substrate improved the wettability of solder alloys, solder bonds were sheared at a lower force leading to decreased shear energy density compared to the smooth Cu surface. A smooth surface finish and the presence of minor amounts of Ag in the alloy improved the integrity of the solder joint. Smoother surface is preferable as it favors failure in the solder matrix.

A Study on High Temperature Oxidation of Titanium Alloys in Solid State Bonding Process

2007 ◽  
Vol 544-545 ◽  
pp. 183-186 ◽  
Author(s):  
Ho Sung Lee ◽  
Jong Hoon Yoon ◽  
Yeong Moo Yi
Keyword(s):  
Solid State ◽  
High Temperature Oxidation ◽  
Oxidation Behavior ◽  
Surface Oxidation ◽  
Bonding Process ◽  
Bonding Interface ◽  
Temperature Oxidation ◽  
Solid State Bonding ◽  
Bonding Condition ◽  
State Diffusion

The surface oxidation behavior was investigated over a range of solid state bonding condition of the Ti-6Al-4V ELI alloy. Since the oxides at the bonding interface may prevent the materials from complete bonding, it is important to understand the oxidation behavior at solid state bonding condition. The activation energy of oxidation of Ti-6Al-4V ELI is estimated to be 318 KJ/mol in an environment of solid state bonding process. For Ti-6Al-4V ELI alloy, strucutral integrity of bonding interface without oxides have been obtained at 850°C applying pressure of 3MPa for 1 hour. Solid state diffusion bonding of Ti-15V-3Cr-3Sn-3Al alloy was also obtained under a pressure of 6MPa for 3 hours at 925°C.

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