Showing papers by "Paul S. Ho published in 1998"

Analysis and modeling verification for thermal-mechanical deformation in flip-chip packages

Abstract: Plastic flip-chip packaging provides a high-performance and low-cost approach for development of electronic packages The underfill material plays a key role in enhancing shear fatigue reliability of the solder bump interconnection between the chip and the substrate However, it raises another reliability concern for delamination at the chip/underfill and the underfill/substrate interfaces This paper focuses on the driving force of the delamination by investigating the stress distribution at the chip/underfill and the underfill/substrate interfaces An in-situ moire interferometry technique was used to measure the thermal deformation in the interface areas of an underfilled flip-chip-on-board package Finite element analysis (FEA) and an analytical solution based on the built-up-bar (BUB) theory were performed to examine the localized stress distribution under thermal loading The correlation between the experimental and modeling results is discussed The use of BUB analysis to examine the effect of material properties on stress and deformation of multilayered packages is also discussed

Structure–property correlation for thin films of semi‐interpenetrating polyimide networks. I. Miscibility, curing, and morphology studies

Abstract: Three different semi-interpenetrating polymer network (semi-IPN) polyimide systems were prepared through blending in solution by using 2 different polyimides, BPDA–PDA and PMDA–ODA (E), and 2 different oligomers, bismaleimide (MDAB) and phenylthynyl-terminated BPDA–PDA (BPDA–PDA–PEPA) oligomers. The oligomers are used as crosslinkers to modify the morphology of polyimides. The results show that both MDAB and PEPA are miscible with BPDA–PDA, but MDAB is immiscible with PMDA–ODA (E). Fourier transform infrared spectrum, dynamic mechanical thermal analysis data, and calculated crosslinking density indicate that there are crosslinking networks in these semi-IPN polyimide systems. In addition, the density and wide-angle X-ray diffraction results confirm that the molecular ordering and packing order are reduced by the addition of oligomers for these semi-IPN polyimide systems. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 261–272, 1998

The effect of crosslinking on thermal and mechanical properties of perfluorocyclobutane aromatic ether polymers

Abstract: As the minimum features in semiconductor devices decrease, it is a new trend to incorporate copper and polymers with dielectric constant less than 3.0 to enhance the performance of the devices. Two fluorinated polymers, poly(biphenyl perfluorocyclobutyl ether) (BPFCB) and poly(1,1,1-triphenyl ethane perfluorocyclobutyl ether) (PFCB), are newly developed polymers with dielectric constants below 3.0. These two polymers have a similar backbone structure, but PFCB has the capability of crosslinking. To know the implications of these two polymers in the semiconductor industry, properties that are important for the integral reliability of Integral Circuits (IC), such as thermal and mechanical properties, should be understood. This comparative study shows that the crosslinking in perfluorocyclobutane aromatic ether polymer can reduce vertical thermal expansion and increase glass transition temperature (T g ) while water absorption, crystalline-like phase, and dielectric constant are slightly increased.

Electromigration study of Al/low dielectric constant polymer and Al/SiO2 dioxide line structures

Abstract: Electromigration reliability is a key concern for implementation of low dielectric constant (low κ) materials for on-chip interconnects. To address this problem, we have carried out a comparative study of electromigration performance for Al(0.5 wt% Cu) line structures formed with tetraethylorthosilicate (TEOS)-based SiO2 and a low κ polymeric dielectric, poly(arylene ether) (PAE). The test structures consisted of 800 μm long single-level line structures with adjacent extrusion monitor lines. Resistometric measurements were performed to measure electromigration lifetime. To supplement lifetime measurements, x-ray diffraction and transmission electron microscopy were used to measure overall grain size and grain orientation distributions, and electron backscattering diffraction was applied to determine local grain orientation and grain boundary characteristics. In addition, scanning electron microscopy was used to examine void morphology. Microstructural analysis has revealed a larger grain size and enhanced...

Structure–property correlation for thin films of semi‐interpenetrating polyimide networks. II. Anisotropy in optical, electrical, thermal, and mechanical properties

Abstract: Three different semi-IPN polyimide systems were prepared through blending in solution by using two different polyimides, such as poly (p-phenylenebiphenyl tetracarbonyimide) (BPDA–PDA) and poly (4,4′-oxydiphylene pyromellitimide) [PMDA–ODA(E)], and two different oligomers, such as bismaleimide (MDAB) and phenylthynyl-terminated BPDA–PDA (BPDA–PDA–PEPA) oligomers. These crosslinkable oligomers are used to modify the morphology of polyimides and, therefore, change the anisotropic properties of the resulting semi-IPN polyimide systems. The results show that the crosslinkable oligomers can disrupt the in-plane molecular arrangement which gives rise to an increase in lateral CTE and vertical CTE and a decrease in birefringence and the Young's modulus. The dielectric constant and water absorption increase with increasing MDAB content but decrease with increasing PEPA content. An empirical correlation between density and volume expansion is observed, indicating a correlation between the volume expansion and free volume expansion and free volume in the semi-IPN polyimide systems. The in-plane modulus decreases but the vertical moduli increases with increasing content of crosslinkable oligomers. In addition, the vertical modulus is affected by the free volume at low stress levels and can be enhanced by crosslinks or by a crystallinelike phase at higher stress levels. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 273–285, 1998

Study of the thermal properties of polymeric dielectric materials by photothermal technique

Abstract: In this paper, we present some results of the newly developed on-wafer photothermal measurement. To study thermal anisotropy, the out-of-plane thermal diffusivity measured from this technique is compared with the in-plane thermal diffusivity by measured by ISTS [1]. In addition to the thermal properties, the agreement with mechanical [2] and optical properties are also shown. The significance of different thermal performance between low K dielectric medium materials and SiO 2 suggests that greater attention should be paid to thermal properties for integrated devices with low K materials.

Electromigration study of Al/low k dielectric line structures

Abstract: Electromigration reliability is a key concern for implementation of low dielectric constant (k) materials for on-chip interconnects. To address this problem, we have carried out a comparative study of electromigration performance for Al(0.5 wt% Cu) line structures formed with TEOS-based SiO2 and a low k polymeric material, poly(arylene ether) (PAE). The test structures consist of 800 µm long single-level ines. Resistometric measurements were performed to determine electromigration lifetime. To supplement lifetime measurements, TEM was used to measure overall grain size and electron back-scatter diffraction (EBSD) was employed to determine the local grain orientation and grain boundary characteristics in the line structure. In addition, SEM was used to examine void morphology. Microstructural analysis revealed a larger grain size and an enhanced (111) texture in PAE-passivated lines compared to TEOS-passivated lines. The differences can be attributed to a high-emperature process used to cure the PAE dielectric. The overall results obtained in this study show reasonably good electromigration performance for low k dielectric interconnects.

Dielectric Anisotropy of Organic Interlayer Dielectrics Confined in Submicron

Abstract: Dielectric anisotropy was studied using two fluorinated polymers(fluorinated polyirnide and fluorinated poly(aryl ether)), which are promising candidate as interlayer dielectrics(LLD). From the measurement of the optical anisotropy, the fluorinated polyimide has larger birefringence than fluorinated poly(aryl ether) because the fluorinated polyimide is a rigid rod-like polymer, while the fluorinated poly(arly ether) has an ether linkage to allow the flexibility. The large optical birefringence in the fluorinated polyimide may indicate the large dielectric anisotropy. The dielectric anisotropy of more flexible fluorinated poly(arly ether) was very similar to the expected anisotropy from optical birefringence, but the fluorinated polyimide with rigid rod-like chains has much smaller dielectric anisotropy than expected in the spin-coated film. From the FTLR spectra of the rigid rod-like polymer, the olecular orientation of the rod-like polymer confined in the submicron gaps is shown to be different from that of the blanket film spin-coated on the substrate. This change of the molecular orientation in the confined submicron gap is responsible for the change of the dielectric anisotropy.

Stress relaxation and void formation in passivated Al(Cu) line structures

Abstract: Relaxation of hydrostatic stresses in passivated Al lines can lead to void formation. We have investigated the long-term stress relaxation behavior of passivated Al(1 wt. % Cu) lines with 3, 1, and 0.5 μm linewidths up to 20 days using a bending beam technique. The results revealed two distinct kinetic regimes for stress relaxation: one due to plastic flow which occurs during an initial short period of annealing, and the other due to stress-induced voiding during long-term annealing. At 250 °C anneal, stress relaxation was dominated by the short-term process, in contrast to the 200 and 150 °C anneals where a clear transition from the short-term to the long-term relaxation was observed. Void density for different linewidths has been measured by TEM and SEM as a function of aging time and temperature. A good correlation between stress relaxation rate and void density was observed for 1, and 0.5 μm lines but not for the 3 μm lines. One micron wide lines show most voiding, whereas 3 and 0.5 μm wide lines show less voiding. This can be attributed to the differences in grain structure where the 1 μm wide lines show a near bamboo structure with some embedded polycrystalline clusters while the 0.5 μm wide lines show an almost perfect bamboo structure. The lower void density for the 0.5 μm wide line suggests that bamboo grain structure reduce the mass transport for voiding and retard void formation. A lower incidence of voiding in 3 μm wide lines can be attributed to a low stress driving force for void formation.

Experimental Investigation on Interfacial Adhesion in Microelectronic Assemblies

Abstract: In this paper, we report recent studies on interface adhesion in flip-chip packaging. The adhesion energies of underfill interfaces found in typical flip-chip packaging pplications are characterized and presented using a racture-mechanics approach. The effects of underfill formulations and changes in polymer top-layer on PCB and chip passivation are also evaluated. The effects of underfill organosilane content, ubstrate surface chemistry and morphology, and underfill filler content are discussed in terms of fundamental mechanisms of adhesion.