Development of Low Stress No-Flow Underfill for Flip-Chip Application
No-Flow Underfill (NUF) technology has been studied in the various ways about cure properties, self fluxing performance, and filler loading. Due to the filler entrapment between solder bump and contact pad on board, no-flow underfills are mostly no filler loading 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 using NUF, and has limited its application to large chip assemblies. However, high-end flip-chip packages are heading towards a high pin count and large chip size with lead free issue and low-k’s. [1] It is expected to develop a low stress underfill because of flip-chip such as low-k chip package has a brittle structure. This paper presents a novel approach to develop for low stress NUF. We have realized flip-chip bonding with a high filler loading of NUF using a local reflow flip-chip bonding assembly process. We have evaluated a deformation of flip-chip package using Shadow Moiré Technique during 260 reflow. This technique is one of the warpage measurement techniques that use a shadow of grating glass. Warpage of IC is decreasing during the reflow process after cooling it recovers initial warpage level. The effects of resin, filler size, filler loading level, fillet size is investigated Filler size, loading level, and fillet size is roughly the same result as reference. As a result, NUF is optimized for lead free soldering process with low stress. Introduction The development trend of flip chip package is the use of Cu/low-k interconnection for higher performance and the use of lead free solder bump for environmental request. Due to low-k materials such as black diamond and SiLK possess weaker mechanical property. [2] It is easy to destruction the low-k layer by package stress such as package warpage. Underfill is one of the factors of package warpage. Lower stress underfill will be optimized the new package. Other side lead free solder bumps possess higher modulus than eutectic solder bump. It is very fragile. The bump cracking was caused by different thermal expansion between substrate (around 15ppm/deg.C) and silicon die (3ppm/deg.C) during thermal cycling test. The bump protection is same as reduction of package stress. This is other development drive of underfill. Capillary underfill (CUF) is currently a leading technology. NUF is one of alternative technology that typically has no filler. Figure 1 shows the process flow of NUF. Previous work has been done to make eutectic solder joint using local reflow flip chip assembly process with filler loaded NUF. [3] This paper presents two approaches that is optimization for lead free solder of NUF and investigation of low stress NUF. Experiment 1. No-Flow Underfills (NUF) NUF were prepared by epoxy-based formulation. Nine NUF were investigated. It contained epoxy resin, hardener, and filler. Table.1 lists the ingredients of each formulation and properties in this study. NUFs were cured at each condition as post curing after reflow. 165deg.C for 90min was required as post curing for NUF-D. Other NUF was cured at 150deg.C for 30min as post curing. Figure 1. Assembly Process Using NUF Table 1. Ingredient of Formulation and properties 2. Test Vehicle The substrate consisted of High Tg FR4 with 0.73 mm thickness and gold plated pad. The test die consisted of daisy chained lead free (Sn / Ag 3.5 / Cu 0.5) solder bump with 9.6 mm x 9.6 mm x 0.72 mm size. 240 bumps were arranged peripheral position. NUF-A NUF-B NUF-C NUF-D NUF-E Base resin Epoxy Epoxy Epoxy Epoxy Epoxy Hardener A B C D E Soft Modifier NO NO NO NO NO Filler loading level [wt%] 50 50 55 65 50 Filler average size [um] 2 2 2 2 2 Viscosity [Pa.s] 150 85 60 55 65 Tg ( DMA ) [C] 190 145 80 90 140 CTE [ppm/C] 40 35 30 25 35 Gelling speed at 150C [sec.] 20 40 120 900 80 NUF-F NUF-G NUF-H NUF-I Base resin Epoxy Epoxy Epoxy Epoxy Hardener B B B B Soft Modifier NO NO LOW HIGH Filler loading level [wt%] 0 50 50 50 Filler average size [um] 0.5 2 2 Viscosity [Pa.s] 12 80 95 110 Tg ( DMA ) [C] 145 145 145 145 CTE [ppm/C] 70 40 35 35 Gelling speed at 150C [sec.] 40 40 40 40
Emerging challenges of underfill for flip chip application
The emerging challenges of underfill technology development for future generations of flip chip applications are reviewed, including capillary underfill materials, underfill processes, and alternative underfill technology. The driving trends of silicon technologies such as copper damascene, low-k dielectrics, low power consumption, and packaging technologies, including shrinking flip chip bump pitch, diameter and gap height, lead-free interconnection, thin die, small form factor and low profile packaging continue to demand innovations in underfill materials, processes, and integration approaches for the technologies.
MT and the Swiss language service providers: an analysis and training perspective
Switzerland is perceived as a highly multilingual country, with four national languages and a solid translation tradition in official, administrative and corporate settings, now even extended to include English. A research case study was set up to investigate the understanding and use of translation and language technologies by Swiss language service providers. This paper highlights some findings, particularly focusing upon the issue of translation automation processes in multilingual documentation production, with a view not only to spot preconceptions or knowledge gaps about MT, but also to 
suggest some training principles. We will argue that training activities ought to present MT systems as 
key aiding components of translator workbenches and, their output, as a valid linguistic resource for further human refining, if necessary. Moreover, in line with the idea that MT can be part and parcel of multilingual content production cycles, we will look at the interaction of MT with controlled language, CAT tools and terminology work. In sum, we will make explicit the usefulness of MT against the 
widespread prejudice that investing in MT does not return any benefits given the ‘low and hilarious quality of its output’, as quoted by most of the interviewees of our case study.