The use of chip scale packages (CSPs) is rapidly expanding, particularly in portable electronic products. Many CSP designs will meet the thermal cycle or thermal shock requirements for these applications. However, mechanical shock and bending requirements often necessitate the use of underfills to increase the mechanical strength of the CSP-to-board connection. This paper examines the assembly process with capillary and fluxing underfills. Issues of solder paste versus flux only, solder flux residue cleaning and reworkability are investigated with the capillary flow underfills. Fluxing underfills eliminate the issues of flux-underfill compatibility, but require placement into a predispensed underfill. Voiding during placement is discussed.To evaluate the relative performance of the underfills, a drop test was performed and the results are presented. All of the underfills significantly (5-6x) improved the reliability in the drop test compared to nonunderfilled parts. Test vehicles were also subjected to liquid-to-liquid thermal shock testing. The use of underfill improved the thermal shock performance by 5x.Index Terms-Chip scale packages, drop test, underfill.
Fluxing underfill eliminates process steps in the assembly of flip chip-on-laminate (FCOL) when compared to conventional capillary flow underfill processing. In the fluxing underfill process, the underfill is dispensed onto the board prior to die placement. During placement, the underfill flows in a "squeeze flow" process until the solder balls contact the pads on the board. The material properties, the dispense pattern and resulting shape, solder mask design pattern, placement force, placement speed, and hold time all impact the placement process and the potential for void formation. A design of experiments was used to optimize the placement process to minimize placement-induced voids. The major factor identified was board design, followed by placement acceleration.During the reflow cycle, the fluxing underfill provides the fluxing action required for good wetting and then cures by the end of the reflow cycle. With small, homogeneous circuit boards it is relatively easy to develop a reflow profile to achieve good solder wetting. However, with complex SMT assemblies involving components with significant thermal mass this is more challenging. To get the large thermal mass components to temperature, the small flip chip die will be at higher temperatures for longer periods of time. Use of predictive software tools to optimize the reflow profile and minimize temperature differences across the board is required. A series of experiments were performed using these tools to optimize the reflow profile of a complex FCOL/SMT assembly. The profile obtained was used to successfully assemble flip chip die with fluxing underfill.In liquid-to-liquid thermal shock testing ( 40 C to +125 C, 5 min hold times and 1 min transition), the characteristic life of the assembly was 1083 cycles and the first failure occurred at 992 cycles.
The paper presents an analysis of ambient temperature influence on measurement accuracy of the smart electricity meter for different values of load current, voltage and frequency. The research scope was covered by the operating temperature range from-40°C to +70°C, which is consistent with the requirements of applicable standards and legal regulations. A meter used in the conducted tests was Iskra MT372 model, which is currently being installed at final customers. Streszczenie. W artykule przedstawiono analizę wpływu temperatury otoczenia na dokładność pomiarów inteligentnego licznika energii elektrycznej dla różnych wartości prądu obciążenia, napięcia i częstotliwości. Badania swoim zakresem objęły temperatury od-40ºC do +70ºC, co jest zgodne z wymaganiami stawianymi inteligentnym licznikom zarówno przez normy, jak i regulacje prawne. W badaniach wykorzystano obecnie instalowany u odbiorców licznik typu Iskra MT372. (Wpływ temperatury na dokładność inteligentnego licznika energii elektrycznej).
The NASA-developed polyimide, is the frontrunner in the race to develop a matrix resin for composites intended for high temperature applications. The properties of PMR-15 depend on the polymer structure. Variations in the structure such as molecular weight, molecular weight distribution and crosslink density, will affect the ultimate mechanical and thermal properties of the material. The polymerization of PMR-15 is complex. Competing reactions in the initial imidization stage, e.g. anhydride formation, can lead to variations in the structure of the oligomers which will affect processing characteristics. This study examines the structure of the prepolymers produced by the thermal imidization of the monomer mixture under different time/temperature conditions. Techniques used include NMR, FTIR, GPC, mass spectrometry and dynamic mechanical spectroscopy. The polymer structures are complex with imide, amide, anhydride, ester, amine and salt all being detected in varying amounts depending on the thermal treatment. Differences in prepolymer molecular weight and molecular weight distribution are also observed. Variations are also seen in prepolymer viscosity and also in volatile evolution at elevated temperatures. Such differences could have a profound effect on processing characteristics.
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