Double-Layer No-Flow Underfill Process for Flip-Chip Applications

©2003 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or distribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.No-flow underfill technology shows potential advances over the conventional underfill technology toward a low-cost flop-chip underfill process. However, due to the filler entrapment in between solder bumps and contact pads on board, no-flow underfills are mostly unfilled or filled with very low filler loading. The high coefficient of thermal expansion (CTE) of the polymer material has significantly lowered the reliability of flip chip assembly and has limited its application to large chip assemblies. This paper presents a double-layer no-flow underfill process approach to incorporate silica filler into a no-flow underfill. Two layers of underfills are applied on to the substrate before chip placement. The bottom underfill layer facing the substrate is fluxed and unfilled; the upper layer facing the chip is filled with silica fillers. The total filler loading of the mixture is estimated to be around 55 wt%. The material properties of each layer of underfills, the underfill mixture, and a control unfilled underfill are characterized using differential scanning calorimeter (DCS), thermo-mechanical analyzer (TMA), dynamic mechanical analyzer (DMA), and a stress rheometer. FB250 daisy-chained test chips are assembled on FR-4 boards using the novel approach. A 100% assembly yield of solder Interconnect is achieved with the double-layer no-flow underfill while in the single-layer no-flow underfill process, no solder joint yield is observed. Scanning electronic microscope (SEM) and optical microscope are used to investigate the cross-section of both assemblies. A US provisional patent has been filed for this invention

Wubeizi Ointment Suppresses Keloid Formation through Modulation of the mTOR Pathway

Background. Wubeizi (Rhus chinensis Mill.) ointment has been shown as an effective treatment for keloids. However, the protective mechanisms of Wubeizi ointment are not fully understood. The mammalian target of rapamycin (mTOR) has been demonstrated to be associated with keloid pathogenesis. In the present study, we investigated if Wubeizi ointment suppressed keloid formation through the modulation of key molecules of the rapamycin (mTOR) pathway including phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (Akt). Methods. A keloid mouse model and human keloid-derived fibroblasts were developed and treated with Galla chinensis. Immunohistochemistry, western blot, and reverse transcription-PCR were used to detect PI3K, PTEN, Akt, and mTOR in keloid tissues and keloid fibroblasts. The apoptosis and proliferation rate of keloid fibroblasts was, respectively, analyzed by flow cytometry according to the MTT assay. Statistical analysis was done using SPSS version 20.0. For two variable comparisons, a two independent samples t-test was used. For multiple variable comparisons, data were analyzed by one-way analysis of variance (ANOVA) followed by pairwise q-tests. Results. Our in vivo and in vitro studies showed that Wubeizi ointment suppressed keloid formation through inhibition of fibroblast proliferation and promotion of fibroblast apoptosis. The underlying basis involves downregulation of p-Akt and p-mTOR as well as upregulation of PTEN. Conclusion. These findings may contribute to a better understanding of the mechanisms of Wubeizi ointment for treating keloids