For wafer level packaging (WLP) applications, BCB, polyimides, epoxies, and PBO are the predominant spin-on dielectric materials used for repassivation, redistribution, and stress buffering. Each of these materials has their respective strengths and weaknesses in process and in reliability. Asahi Glass Co., LTD has developed a new spin-on dielectric polymer (ALX) designed for WLP applications that provides a unique set of material properties coupled with a low curing temperature. We have previously presented process evaluation and optimization data on ALX polymer material, which showed an application process similar to BCB with wide process latitude. In this paper we present the results of a study done to evaluate the performance of ALX polymers in WLP test structures fabricated at RTI International. Typical solder bumped repassivation and bump-onpolymer test structures have been fabricated using ALX and BCB and evaluated through bump shear tests. We have also evaluated the adhesion of ALX to typical materials encountered in WLP structures through shear testing free-standing polymer structures.

“Real 3D” integration 3DIC Integration in its true definition [1] has a long history. As early as 1985, Richard P. Feynman expressed this vision [2]: “Another direction of improvement of computing power is to make physical machines three dimensional instead of all on a surface of a chip. That can be done in stages instead of all at once you can have several layers and then add many more layers as time goes on” [2].

Mechanical properties are typically used as a first-order comparison of different thin film microelectronic polymers. Tensile testing is commonly used to determine such mechanical properties (i.e. Young's modulus, % elongation, tensile strength). Having accurate values generated under known, standardized test conditions is therefore an important consideration. We have found that the method of sample preparation and fixturing during test, gage length (length of the sample under test), testing system, and test methodology can have a significant impact on the mechanical property measurements that are derived from tensile testing. This study focuses on low curing temperature (~ 200°C) polymers and the determination of their mechanical properties using a uniform testing approach to eliminate sample preparation and testing variations. We find the values for Young's modulus and % elongation when done by different manufacturers, using different test systems and methodologies, can vary significantly from those reported herein.

EXECUTIVE OVERVIEW Redistribution technology was developed out of necessity to allow fan-in area array packaging (bumping) to take hold when very few chips were being designed for area array. In the intervening years it has been instrumental in developing many of the newer packaging technologies such as wafer-level packaging (WLP), fan-out packaging, and TSV-based interposers and chip stacks.

As IC scaling continues to shrink transistors, the increased number of circuits per chip requires more I/O per unit area (Rent's rule). High I/O count, the need for smaller form factors and the need for better electrical performance drove the technological change towards die being interconnected (assembled) by area array techniques. This review will examine this evolution from die wire bonded on lead frames to flip chip die in wafer level or area array packages and discuss emerging technologies such as copper pillar bumps, fan out packaging, integrated passives, and 3D integration..

We present the results of study on the manufacturability and reliability of ALX211 polymer in wafer level packaging processes and structures. Previously, we studied the processing windows of ALX211 polymer, where process parameters were studied in lab conditions. The typical manufacturing environment differs from the laboratory environment in that delays between processing steps are typical and unavoidable. Determining the impact of these delays on the stability of the process is critical for determining how the material will perform in a manufacturing line. In this paper, we present new data on the impact of hold times between the main process sequences for the ALX211 process and show that the process is stable with hold times up to 24 hours between process steps. In addition, we present reliability results comparing the performance of polyimide, BCB, and ALX211 as evaluated in a bump-on-polymer test structure. Results of bump shear tests after process completion and after exposure to multiple reflow cycles are presented, as well as results of board level temperature cycling testing.

In this paper we present the results of a study done to compare the new Asahi Glass ALX polymers with other microelectronic polymers in typical WLP structures. We present property data on ALX-211, including spin speed curves and resolution plots, planarization, thermal stability and stress data and adhesion as evaluated using polymer bump shear testing. We have examined the processing of ALX-211 and developed a standard process flow for these materials. We have used ALX-211 in a typical bump-on-polymer process flow, with eutectic Sn/Pb solder bumps, and compared its performance to that of BCB through solder bump shear testing.

In this paper we present the results of a study done to compare and contrast BCB and ALX polymers in typical WLP structures fabricated at RTI. Based on initial studies of the materials vendor, Asahi Glass Corp, AGC, we have examined the processing parameter space of ALX-211, in order to develop scalable manufacturing processes for these films. We present process flow and photo property data on ALX-211, including spin speed curves and resolution plots. We also present data on the planarization capability of AL polymer, the adhesion of ALX-211 to metals and inorganic dielectric materials as evaluated using polymer bump shear structures. We have incorporated the ALX-211 polymer into a typical bump-on-polymer process flow, with eutectic Sn/Pb solder bumps, to compare its performance to that of BCB through solder bump shear testing.

Fluorene arylene copolymers are a class of aromatic macromolecules that have an alternating backbone structure consisting of a 9,9-dialkylfluorene together with one (or more) additional aromatic group(s). Fluorene when combined with chromophoric and/or charge transporting aromatic monomers to form polyfluorenes have received a great deal of attention over the last several years as the emissive layer in polymeric light emitting diodes. The emission of green, red, or blue light can be controlled by the choice of the aryl backbone segments and alkyl side groups in the polymer. More recently, polyfluorenes have been designed and evaluated As the organic semiconducting layer in polymeric field effect transistors (pFETs). This work has led to a class of polymeric semiconductors with an excellent combination of charge mobility, environmental stability, and processability. These polymers have also been shown to have optoelectronic properties. The high optical density, high charge carrier mobility, and the potential to tune the absorption spectra makes this class of materials an ideal candidate for further study in the area of organic photovoltaics. This paper reviews the synthesis and characterization of polyfluorenes, focusing on the optimization of electronic properties for the conversion of light into electric current.

Organic and polymer semiconductors are being explored by numerous research and development organizations as a means to create unique, low cost electronic devices. Though it is clear that these materials cannot match the performance of inorganic crystalline semiconductors (i.e. silicon) they have an advantage in that they can be fabricated into thin, mechanically robust films on a variety of low cost substrates by low cost processing techniques such as printing. This paper will review the area of organic and polymer semiconductors for use in thin film transistors. Examples of materials that have been explored and their critical properties will be covered.

Several wafer level chip scale package (WLCSP) technologies have been developed which generate fully packaged and tested chips on the wafer prior to dicing. Many of these technologies are based on simple peripheral pad redistribution technology followed by attachment of 0.3-0.5 mm solder balls. The larger standoff generated by these solder balls result in better reliability for the WLCSP's when underfill is not used than for equivalent flip chip parts. Rambus/sup TM/ RDRAM and integrated passives are two applications that should see wide acceptance of WLCSP packages.

The toughness of CYCLOTENE (TM) divinylsiloxane-bisbenzocyclobutene (BCB) based polymer resins from The Dow Chemical Company, is enhanced by incorporation of a second component in the polymer matrix. Thin films of modified BCB resin have significantly improved elongation at break. Excellent properties of BCB resin such as low dielectric constant and dissipation factor, low moisture up-take and higher than 350 degreesC glass transition temperature are maintained in this modified BCB material. Isothermal TGA of BCB resin with 20 wt. % additive demonstrates thermal stability of less than 1 % weight loss per hr at 325 degreesC. Residual stress of modified BCB resin thin film on a silicon wafer is about the same as BCB resin. A transmission electron micrography (TEM) study of BCB film with up to 18 wt. % of additive does not show discrete domains of the second component. At 20 % loading, some domains with approximately 0.1 mum diameter are observed. As the amount of additive increases, the size of the domains increases. Modified BCB resin formulations are photo-definable with good resolution and film retention.

With the demand for higher interconnect density increasing, the ability of polymeric insulation to resist current flow and protect circuits from corrosion is becoming more and more important. BCB polymer is being used commercially on many high density devices which must function in non-hermetic environments. It was therefore of interest to quantify the change in resistance and leakage current (under temp-humidity-bias), of BCB encapsulated circuits by conducting surface insulation resistance (SIR) and triple track testing (TTT). SIR of all the Cyclotene samples ranged from 7.5/spl times/10/sup 8/ to 8.8/spl times/10/sup 9/ /spl Omega/. TTT reveals stable resistance of all samples past 500 hours. Leakage current measurements of /spl les/4/spl times/10/sup -11/ amperes were observed. The BCB samples show results equal to or better than the Dow Corning vulcanized rubber control, indicating excellent circuit protection capability.

Multilevel high-density substrates require wirebonding to bondpads which are located over thick polymer dielectric layers. We have studied the ability to thermosonically wirebond gold onto Cu/Ni/Au surface metallurgy consisting of 2 mu m Cu representing the bondpad followed by 1 to 4 mu m electroless Ni and I pm electroless Au over 5 - 20 mu m of BCB (CYCLOTENE(TM)) dielectric. Results suggest that backcooling during sputter roughening of the BCB is important to promoting adhesion between the sputtered Ti sublayer and BCB. At BCB thicknesses of 0 to 10 mu m and any Ni thicknesses in the range elf 1 to 4 mu m, the bonds passed pull testing exhibiting a strength of 9 grams and a clean tensile failure of the bond wire. Bonding over 15 to 20 mu m of underlying BCB required higher bonding power and dwell times but reliable bonds could be made with reasonable bonding parameters if 3 or 4 mu m of Ni was present to stiffen the pad. Without sufficient Ni thickness the bondpads ripped from the substrate during bond pull testing revealing cohesive fracture damage to the BCB under the pad.