Using standalone SAC solder joints in BGA and CSP assemblies does not provide the level of thermal fatigue resistance required by automotive, aerospace, military and semiconductor manufacturers.
To ensure that these assembled components are able to withstand long periods of exposure in harsh environments, capillary underfilling using ALPHA HiTech CU21-3240, from MacDermid Alpha Electronics Solutions, is the solution.
Typically, rework on the components is not used in these applications. Non-reworkable underfills such as ALPHA HiTech CU21-3240 allow a higher filler content in the formulation to lower the Coefficient Thermal Expansion [α] and increase the Glass Transition Temperature [Tg], enabling increased strengthening for BGA and CSP components assembled with SAC solder joints. Thus, increasing the viscosity and Thixotropic Index of the material. Due to these characteristics the flow rate will be slow, but this can be significantly increased with heat applied at the substrate level during the dispensing process.
Fig 1. Radar Chart on ALPHA HiTech CU21-3240 Capillary Underfill
The high filler content of ALPHA HiTech CU21-3240 requires a preheat temperature of 70 – 100°C at substrate level to increase the flow rate to cover the footprint beneath the component effectively during the dispensing process. A faster flow is achievable with higher temperatures.
Table 1. Flow Rate Performance at various temperatures
The Transition Glass of ALPHA HiTech CU21-3240 is high at 165°C, and both the α1 and α2 are low, 31 ppm and 105 ppm respectively. The cured material in a subjected thermal cycling -40 + 125°C test [TCT], with the temperature comfortably lower than Tg, will always be with the α1 value. Lower expansion properties are generally deemed able to provide better thermal cycle passes for SAC type solder joints. In automotive applications the following are the thermal cycle test requirements:
- In Cabin: -40/105°C, 15-30 minutes dwell, 1000 – 2000 cycles requirement
- Advanced Driver Assistance Systems [ADAS]: -40 + 125°C, 15-30 minutes dwell, pass up to 3000 cycles requirement
ALPHA HiTech CU21-3240 enables the reinforcement effect to generate a thermal cycle test pass of up to 5000 cycles on assembled CVBGA360 [10-mm X 10-mm body size, 0.25-mm SAC 305 solder sphere, 0.4 mm pitch] with SAC305 solder joints, equalling exceptional thermal fatigue resistance.
ALPHA HiTech CU21-3240 underfill is part of the range of ALPHA HiTech materials including underfills, edgebonds, encapsulants and adhesives from MacDermid Alpha Electronics Solutions.
MacDermid Alpha Electronics Solutions enables electronics interconnection through the innovative specialty chemicals and materials from our Alpha, Compugraphics, Electrolube, Kester, and MacDermid Enthone brands. We serve all global regions and all steps of device manufacturing within every segment of the electronics supply chain. The experts in our Semiconductor Solutions, Circuitry Solutions, and Assembly Solutions divisions collaborate with OEMs and fabricators in the implementation of new technologies that redefine what is possible in device design. Our world class technical service is constantly at hand to ensure optimized outcomes in yield and productivity. Our solutions can increase throughput, reduce carbon footprints, lower total cost of ownership, and enable electronics innovation.
To learn more about ALPHA HiTech CU21-3240 and our range of high reliability materials for harsh-end use environments please visit the newly launched MacDermid Alpha website.
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