Packaging and Assembly Challenges for 2.5D/3D Devices

2016 ◽  
Vol 2016 (DPC) ◽  
pp. 001161-001191 ◽  
Author(s):  
Gerald Beyer ◽  
Kenneth Rebibis ◽  
Arnita Podpod ◽  
Francisco Cadacio ◽  
Teng Wang ◽  
...  
Keyword(s):  
Flip Chip ◽  
Mechanical Stability ◽  
Coefficient Of Thermal Expansion ◽  
Wafer Level ◽  
Large Area ◽  
Molding Process ◽  
Process Step ◽  
Joint Formation ◽  
Bonding Force ◽  
Underfill Material

The continuous development of 2.5D/3D packaging and stack assembly technologies has enabled different ways of producing advanced packages for the said devices. Advancement in D2D, D2W and W2W bonding have allowed these devices to be a step closer to being fully manufactured in volume. Thermo-compression bonding (TCB) process in combination with a pre-applied underfill material (WLUF/NUF) have been developed and investigated for assembling 2.5D and 3D devices with fine pitch (10μm - 40 μm) μbumps. This assembly step though developed, is not without challenges. There is a need to select the right underfill material based on its mechanical and chemical properties which could contribute to issues such as die warping, voiding and non-wetting of μbumps. These materials should also be able to withstand several thermal steps within the entire stack assembly process and is able to pass reliability testing. During the TCB process, bonding forces have a profound impact on the joint formation behavior on the μbumps. A low bonding force could produce a joint formation with a lot of underfill filler entrapment and an incomplete reaction of the solder. A higher bonding force leads to more solder squeezing-out, leaving a thin and completely reacted intermetallic compound (IMC) layer in the joints. The D2D, D2W and W2W assembled chips can then be packaged into a standard flip chip component using laminate BGA substrates. But even with this volume manufacturing process, the introduction of 2.5D/3D stack devices brings another set of challenges to an existing assembly infrastructure. Challenges such as the handling of the stacked devices, the CTE mismatches of an entirely new set of materials and the constant scaling in FC bump (Cu Pillar or C4) pitches in an existing infrastructure remain. The limitations of organic BGA packages in terms of CTE mismatches and costs gave rise to Fan-out Wafer Level Packages (FOWLP) or a technique also known as wafer reconstruction. However, there are certain tradeoffs particularly in the molding process step of fully D2W stacked or reconstructed 300 mm wafers. Molding such a large area of stacked chips with very narrow gaps of around 50μm to 300μm is a major challenge especially in trying to maintain the flatness of the wafer for succeeding wafer level processing steps. The large warpage of over molded (D2W or reconstructed) wafers is due to the coefficient of thermal expansion (CTE) mismatch between silicon and the reconstruction material. Therefore careful selection of materials and design of reconstructed structures is needed. Other techniques to keep the D2W or reconstructed assemblies are being developed and evaluated. Also by selecting an FOWLP or reconstructed wafer type of package, the integration of temporary bonding materials (TBMs) in TCB and wafer molding becomes a challenge. In order to produce the reconstructed wafer or the thinned D2W assembly, thermal and mechanical stability is required for such a material. In summary, the combination of advance stacking techniques and materials within certain 2.5D/3D integration flows could produce a low-cost and reliable 3D package. But these combinations will pose a number of challenges that needs to be addressed. This paper will discuss the different integration flows, stacking and packaging assembly techniques (and their challenges) that could make volume manufacturing possible for 2.5D/3D devices in the future.

Reduction of Thermal Stress - Part II: Passivation Thickness Optimization of FLATPV Surface Bump Design

2017 ◽  
Vol 2017 (1) ◽  
pp. 000508-000512
Author(s):  
Raj Sekar Sethu ◽  
Salil Hari Kulkarni ◽  
How Ung Ha ◽  
Kok Heng Soon
Keyword(s):  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Passivation Layer ◽  
Fracture Rate ◽  
Thickness Optimization ◽  
Wafer Level ◽  
Passivation Layers ◽  
Solder Balls ◽  
Interaction Stress ◽  
Underfill Material

Abstract Surface undulations on semiconductor devices can increase chip package interaction stress that leads to possible passivation cracking. This is especially so for flip chip interconnects which have solder balls that are in contact with the passivation layer. The solder balls have a larger Coefficient of Thermal Expansion (CTE) compared to the passivation layers and this can lead to increase in fracture rate especially during reflow cooling. The other factor is the underfill material. The flat passivation design can reduce the chip package interaction for underfill material but it needed to be evaluated numerically for wafer level stress before being touted as a solution towards reducing passivation cracks. In Part II of this series of papers, the flat passivation layer thicknesses were numerically simulated and modified using response surface methodology design of experiments (RSM DOE) techniques. The optimized passivation layer thickness showed decreased stress which was validated using a simulation confirmation run.

A Heterogeneous Array of Off-Chip Interconnects for Optimum Mechanical and Electrical Performance

2007 ◽  
Vol 129 (4) ◽  
pp. 460-468 ◽  
Author(s):  
Karan Kacker ◽  
Thomas Sokol ◽  
Wansuk Yun ◽  
Madhavan Swaminathan ◽  
Suresh K. Sitaraman
Keyword(s):  
Flip Chip ◽  
Dielectric Material ◽  
Coefficient Of Thermal Expansion ◽  
Semiconductor Industry ◽  
Organic Substrate ◽  
Electrical Performance ◽  
Integrative Approach ◽  
Wafer Level ◽  
Target Values ◽  
Low K

Demand for off-chip bandwidth has continued to increase. It is projected by the Semiconductor Industry Association in their International Technology Roadmap for Semiconductors that by the year 2015, the chip-to-substrate area-array input-output interconnects will require a pitch of 80 μm. Compliant off-chip interconnects show great potential to address these needs. G-Helix is a lithography-based electroplated compliant interconnect that can be fabricated at the wafer level. G-Helix interconnects exhibit excellent compliance in all three orthogonal directions, and can accommodate the coefficient of thermal expansion (CTE) mismatch between the silicon die and the organic substrate without requiring an underfill. Also, these compliant interconnects are less likely to crack or delaminate the low-k dielectric material in current and future integrated circuits. The interconnects are potentially cost effective because they can be fabricated in batch at the wafer level and using conventional wafer fabrication infrastructure. In this paper, we present an integrative approach, which uses interconnects with varying compliance and thus varying electrical performance from the center to the edge of the die. Using such a varying geometry from the center to the edge of the die, the system performance can be tailored by balancing electrical requirements against thermomechanical reliability concerns. The test vehicle design to assess the reliability and electrical performance of the interconnects is also presented. Preliminary fabrication results for the integrative approach are presented and show the viability of the fabrication procedure. The results from reliability experiments of helix interconnects assembled on an organic substrate are also presented. Initial results from the thermal cycling experiments are promising. Results from mechanical characterization experiments are also presented and show that the out-of-plane compliance exceeds target values recommended by industry experts. Finally, through finite element analysis simulations, it is demonstrated that the die stresses induced by the compliant interconnects are an order of magnitude lower than the die stresses in flip chip on board (FCOB) assemblies, and hence the compliant interconnects are not likely to crack or delaminate low-k dielectric material.

Underfill Assessments and Validations for Low-k FCBGA

2006 ◽  
Author(s):  
Nicholas Kao ◽  
Jeng Yuan Lai ◽  
Jase Jiang ◽  
Yu Po Wang ◽  
C. S. Hsiao
Keyword(s):  
Finite Element ◽  
High Speed ◽  
Flip Chip ◽  
Failure Modes ◽  
Solder Bump ◽  
Material Selection ◽  
Coefficient Of Thermal Expansion ◽  
Electrical Performance ◽  
Low K ◽  
Underfill Material

With the trend of electronic consumer product toward more functionality, high performance and miniaturization, IC chip is required to deliver more I/Os signals and better electrical characteristics under same package form factor. Thus, Flip Chip BGA (FCBGA) package was developed to meet those requirements offering better electrical performance, more I/O pins accommodation and high transmission speed. For high-speed application, the low dielectric constant (low-k) material that can effectively reduce the signal delays is extensively used in IC chips. However, the low-k material possesses fragile mechanical property and high coefficient of thermal expansion (CTE) compared with silicon chip, which raises the reliability concerns of low-k material integrated into IC chip. The typical reliability failure modes are low-k layer delamination and bump crack under temperature loading during assembly and reliability test. Delamination is occurred in the interface between low-k dielectric layers and underfill material at chip corner. Bump crack is at Under Bump Metallization (UBM) corner. Thus, the adequate underfill material selection becomes very important for both solder bump and low-k chips [1]. This paper mainly characterized FCBGA underfill materials to guide the adequate candidates to prevent failures on low-k chip and solder bump. Firstly, test vehicle was a FCBGA package with heat spreader and was investigated the thermal stress by finite element models. In order to analyze localized low-k structures, sub-modeling technique is used for underfill characterizations. Then, the proper underfill candidates picked from modeling results were experimentally validated by reliability tests. Finally, various low-k FCBGA package structures were also studied with same finite element technique.

Advances in Temporary Bonding and Debonding Technologies for use with Wafer-Level System-in-Package (WLSiP) and Fan-Out Wafer-Level Packaging (FOWLP) Processes

2018 ◽  
Vol 2018 (1) ◽  
pp. 000051-000056 ◽  
Author(s):  
Michelle Fowler ◽  
John P. Massey ◽  
Matthew Koch ◽  
Kevin Edwards ◽  
Tanja Braun ◽  
...  
Keyword(s):  
Coefficient Of Thermal Expansion ◽  
Active Area ◽  
Vertical Deformation ◽  
Level System ◽  
Wafer Level ◽  
Molding Process ◽  
Bonding Material ◽  
Wafer Level Packaging ◽  
Temporary Bonding ◽  
Mechanical Release

Abstract Today's complex fan-out wafer-level packaging (FOWLP) processes include the use of redistribution layers (RDL) and reconstituted wafers with epoxy mold compound (EMC) for use in heterogeneous integration [1]. Wafer-level system-in-package (WLSiP) uses fan-out wafer-level packaging (FOWLP) to build the system-in-package (SiP) by attaching know-good die (KGD) in a chip-first process to a tape laminated temporary carrier. If the dies are attached in a die-up configuration (active area facing up) and then over-molded with EMC, contact pads on the embedded die are exposed during the backside grind process. During the RDL build, the temporary carrier supplies mechanical support for the thinned substrate. In a die-down configuration with the active area facing down (eWLB), the temporary carrier is removed after the molding process thus exposing the contact pads for RDL build and solder ball mount. The ideal chip attachment scheme should minimize lateral movement of the die during over-mold (die shift) and also minimize vertical deformation of the bonding material. Thermal release tape provides a convenient way to attach die to a carrier prior to over-molding with EMC. However, not all bonding materials are suitable for presentation in tape form, so the material used in the tape may not be the optimal choice. An alternative method is to directly apply temporary bonding material to the carrier substrate. This enables the use of bonding materials with higher melt viscosity and improved thermal stability, resulting in less vertical deformation during die placement, and reduced die shift during over-molding. The bonding material will ideally have high adhesion to the EMC wafer to prevent delamination in the bond line during downstream processing. Stack stress and warpage is a major concern which causes handling and alignment problems during processing. The bonding material and carrier will need to be specifically suited to minimize the effects of stress in the compound wafer. Such material must balance rigidity with warp to prevent lateral die shift and deformation induced by coefficient of thermal expansion (CTE) mismatch between the carrier and EMC material [2]. Bonding materials must also have enough adhesion to the EMC material to overcome such stress without bond failure for an associated debond path (such as laser or mechanical release). In this experiment, we will examine a thermoplastic bonding material in combination with different release materials, addressing die shift, and deformation after EMC processing. Successful pairs will then undergo carrier release using either mechanical release or laser ablation release technology.

Design and fabrication of MEMS-type compliant overhang flip-chip interconnect for RF applications

2015 ◽  
Vol 2015 (DPC) ◽  
pp. 002082-002094
Author(s):  
Pingye Xu ◽  
Michael C. Hamilton
Keyword(s):  
Solder Ball ◽  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Organic Substrate ◽  
Process Temperature ◽  
High Yield ◽  
Wafer Level ◽  
Micro Fabrication ◽  
Compliant Interconnect ◽  
Sac Solder

With the increase of I/O density and scaling of interconnects, conventional solder ball interconnects are required to be made smaller. As a result, the reliability of the conventional solder ball flip-chip interconnects worsens. One method to mitigate this issue is by using underfill. However, underfill undermines the reworkability of the solder joints and is challenging to apply when the gap between chip and substrate is small. Another approach to enhance the reliability is to use taller solder ball interconnects, which is however usually more costly. Instead of using conventional solder ball interconnects, compliant interconnects have also been researched in the past few decades to mitigate the reliability issue. The use of compliant structures can compensate for the coefficient of thermal expansion (CTE) mismatch between a Si chip and an organic substrate. In this work, we present the design and fabrication of MEMS-type compliant overhang flip-chip interconnects. The structures are placed at the end of a coplanar waveguide (CPW) as interconnects between CPWs to research their performance at radio frequency (RF). A micro-fabrication process was adopted to build the interconnects. The CPWs are fabricated using conventional e-beam deposition followed by photolithography and then copper electroplating. The compliant overhangs were fabricated on top of a dome of reflowed photoresist on the CPWs to form a curved shape. The reflow and hard bake of the photoresist requires a process temperature of above 220 °C, which is similar to the reflow temperature of a Sn-Ag-Cu (SAC) solder. Therefore we believe our process is compatible with SAC solder processing infrastructures in terms of process temperature. The fabricated structures show high yield and uniformity. Due to the use of a micro-fabrication based process, the structures have the potential to be scaled and be compatible to wafer level packaging. The CPWs were then flip-chip bonded with the compliant interconnect as transitions. The RF performance of the interconnects up to 50 GHz will be presented.

2nd Level Reliability Improvement on WLCSP

2010 ◽  
Vol 2010 (1) ◽  
pp. 000333-000338
Author(s):  
Seungwook Park ◽  
Jupyo Hong ◽  
Changbae Lee ◽  
Sunhee Moon ◽  
Jinsoo Kim ◽  
...  
Keyword(s):  
Solder Ball ◽  
Coefficient Of Thermal Expansion ◽  
Drop Test ◽  
Wafer Level ◽  
Molding Process ◽  
Property Variation ◽  
Chip Scale Package ◽  
Low Modulus ◽  
Market Needs ◽  
Reliability Issue

Recently the package market is demanding the smaller package size and the lower impedance electrical path with a short interconnection. The wafer level chip scale package is one of them, which has the solution of the market needs above. However, WLCSP technology is still not fully accepted on the large device size that is larger than 5mm × 5mm. It needs to overcome 2nd level reliability issue on both solder joint and drop reliability test. To improve 2nd level reliability, we need to apply the longer stand–off design such as Cu –post and double solder ball instead of single solder ball, and low modulus material on polymer layer under the solder pad for releasing thermal stress which result in the solder joints crack due to CTEs (Coefficient of Thermal Expansion) mismatch between organic PCB and WLCSP. In this paper, the double ball structure is introduced as one of them can provide the longer stand off. In addition of improving 2nd level reliability and drop test it may need to apply different solder ball component properties to increase Thermal cycling and drop test. The WLCSP structured a double solder ball showed a better 2nd level reliability result. This paper describes the molding process for double ball process and 2nd level reliability by solder property variation.

Warpage Analysis of Wafers With Film Coating

2001 ◽  
Author(s):  
Hai Ding ◽  
I. Charles Ume ◽  
Cheng Zhang
Keyword(s):  
Young’S Modulus ◽  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Young's Modulus ◽  
Film Coating ◽  
Wafer Level ◽  
Element Analysis ◽  
Low Temperature Storage ◽  
Shadow Moire ◽  
Shadow Moiré

Abstract Wafer-level packaging (WLP) is one of the trends of electronic packaging in the 21st century. Since 1994, many companies have released WLP licenses. One of the common concerns among these various approaches is wafer warpage. Warpage of wafer tends to introduces crack or delamination during dicing and low temperature storage process. After wafer dicing, warpage could reduce the quality of each package in the long run. Many documented works indicated that in the design and implementation of WLP, some key parameters have to be carefully considered and closely controlled to ensure higher packaging quality with the minimum warpage. For the case of wafer-level flip chip, the key parameters are Young’s modulus, thickness, and coefficient of thermal expansion (CTE) of underfill. In this research, an experimental design and statistical methods have been used to identify the model structure and parameters that are critical to the warpage of wafers. Regression models were identified based on the data obtained from finite element analysis (FEA) that is verified by shadow Moiré experiments. According to the models, the CTE, the coupling of Young’s modulus and CTE, and the coupling of thickness and CTE of underfill primarily determine wafer warpage. Further FEA and shadow Moiré experiments indicate that the models are capable of predicting of wafer warpage in the process of WLP.

Development of No Flow Underfills for Lead-Free Flip Chip Applications

2006 ◽  
Author(s):  
Kaustubh Nagarkar ◽  
Tan Zhang ◽  
David Esler ◽  
David Simon ◽  
Paul Gillespie ◽  
...  
Keyword(s):  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Stencil Printing ◽  
Significant Research ◽  
Flip Chip Packaging ◽  
Chip Carrier ◽  
Packaging Industry ◽  
The Impact ◽  
Semiconductor Packaging ◽  
Underfill Material

Flip chip packaging is one of the fastest growing segments in electronics packaging technology. The semiconductor packaging industry is continuing to migrate towards Pb-free electronics assembly. Therefore, the development of compatible materials for Pb-free flip chip packaging is critical to this transition [1]. Flip chip devices are commonly underfilled to compensate for the mismatch in the Coefficient of Thermal Expansion (CTE) between the die and the chip carrier. The No Flow Underfill (NFU) process is a type that can increase the throughput of the flip chip assembly process and reduce manufacturing costs. Significant research has been performed to develop NFUs for eutectic applications. However, further research is required for the development of NFUs that are compatible with the Pb-free solders and the high temperature reflow process associated with these solders. In this paper, the challenges associated with the development of 'filled' underfill formulations for assembly with the 95.5Sn/3.8Ag/0.7Cu bumped flip chip devices are discussed. The effects of process variables that affect voiding in the underfill layer have been presented. The impact on voiding due to stencil printing of the underfill has been discussed. The impact on assembly reliability due to the underfill material properties has also been reported.

Development of Novel Filler Technology for No-Flow and Wafer Level Underfill Materials

2005 ◽  
Vol 127 (2) ◽  
pp. 77-85 ◽  
Author(s):  
Slawomir Rubinsztajn ◽  
Donald Buckley ◽  
John Campbell ◽  
David Esler ◽  
Eric Fiveland ◽  
...  
Keyword(s):  
Cost Reduction ◽  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Organic Substrate ◽  
Operating Speed ◽  
Wafer Level ◽  
Package Design ◽  
Chip Technology ◽  
Package Size ◽  
Package Reliability

Flip chip technology is one of the fastest growing segments of electronic packaging with growth being driven by the demands such as cost reduction, increase of input/output density, package size reduction and higher operating speed requirements. Unfortunately, flip chip package design has a significant drawback related to the mismatch of coefficient of thermal expansion (CTE) between the silicon die and the organic substrate, which leads to premature failures of the package. Package reliability can be improved by the application of an underfill. In this paper, we report the development of novel underfill materials utilizing nano-filler technology, which provides a previously unobtainable balance of low CTE and good solder joint formation.

Warpage Analysis of Underfilled Wafers

2004 ◽  
Vol 126 (2) ◽  
pp. 265-270 ◽  
Author(s):  
Hai Ding ◽  
I. Charles Ume ◽  
Cheng Zhang
Keyword(s):  
Young’S Modulus ◽  
Electronic Packaging ◽  
Flip Chip ◽  
Coefficient Of Thermal Expansion ◽  
Young's Modulus ◽  
Wafer Level ◽  
Element Analysis ◽  
Low Temperature Storage ◽  
Shadow Moire ◽  
Shadow Moiré

Wafer-level packaging (WLP) is one of the future trends in electronic packaging. Since 1994, many companies have released various WLP licenses. One of the common concerns of WLP is wafer warpage. Warpage of wafers tends to introduce cracking or delamination during dicing and low temperature storage processes. After wafer dicing, warpage could affect the quality of the dies and shorten the life of each packaged product. Many documented works indicated that in the design and implementation of multilayer structured electronic packaging products, some key parameters must be carefully considered and closely controlled to ensure the best packaging quality with the minimum warpage. During the wafer-level flip chip assembly process, the application of underfill on the whole wafer is a critical step. In this step, the key underfill parameters that affect wafer warpage are Young’s modulus, thickness, and coefficient of thermal expansion (CTE). In this paper, an experimental design and statistical methods were used to identify the model structure and parameters that are critical to the warpage of wafers. Bilinear regression models were identified based on the data obtained from finite element analysis (FEA) that was verified by shadow moire´ experiments. In FEA, the underfilled wafer structure is simplified to consisting of two layers of linear elastic materials. According to the models, the CTE, the coupling of Young’s modulus and CTE, and the coupling of thickness and CTE primarily determine wafer warpage. Further FEA and shadow moire´ experiments indicate that the models are capable of predicting wafer warpage in the WLP processes.

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