Whitepapers

Working with LED manufacturers reveals a common problem: how to effectively add phosphor to the silicone encapsulant without having it settle or incur processing problems like curing too soon, deairing and bubbles. A study was done to evaluate two silicone encapsulation materials for their ability to maintain phosphor in solution for ease of manufacturing...

Working with LED manufacturers reveals a common problem: how to effectively add phosphor to the silicone encapsulant without having it settle or incur processing problems like curing too soon, deairing and bubbles. A study was done to evaluate two silicone encapsulation materials for their ability to maintain phosphor in solution for ease of manufacturing and production of white light emitting diodes. The phosphor dispersions were evaluated over a large temperature range, -40 to 150°C, to attempt to understand the material in the most broad and general way. This temperature range was subsequently divided into storage, -40°C to –20°C, dispensing, 15°C to 35°C, and curing, > 40°C, recognizing these portions of the range have unique requirements for production applications.

Silicone adhesives and coatings have been used for over five decades in the Aerospace industry. Silicone's ability to maintain its elasticity and low modulus over a broad temperature range, -130ºC to 260°C, provides excellent utility in space, where spacecraft are often exposed to these extreme temperatures. A major drawback is...

Silicone adhesives and coatings have been used for over five decades in the Aerospace industry. Silicone's ability to maintain its elasticity and low modulus over a broad temperature range, -130ºC to 260°C, provides excellent utility in space, where spacecraft are often exposed to these extreme temperatures. A major drawback is silicone compounds with high vapor pressure can outgas from the polymer matrix and cause subsequent contamination of expensive equipment and devices. The National Aeronautics & Space Administration (NASA) and the European Space Agency (ESA) recommend testing low outgassing materials per ASTM E 595 prior to use in space which require a maximum Total Mass Loss (TML) of 1% and Collected Volatile Condensable Material (CVCM) of 0.1%. Although a standard for many years, many in the industry question whether these specifications are low enough. This paper characterizes Ultra Low Outgassing™ silicone materials with TML and CVCM one-tenth the standard ASTM E 595 specifications. ASTM E 1559 results are also examined to compare the outgassing behavior of different silicone material

This study evaluates twenty-one samples for their change in optical transmission due to a 680-6800J/cm2 dose of UV radiation. Samples were made from UV curing acrylate, epoxy and silicone chemistries. All samples were prepared and exposed the same way so that comparisons between the samples would be meaningful. Given the same dosage...

This study evaluates twenty-one samples for their change in optical transmission due to a 680-6800J/cm2 dose of UV radiation. Samples were made from UV curing acrylate, epoxy and silicone chemistries. All samples were prepared and exposed the same way so that comparisons between the samples would be meaningful. Given the same dosage of UV, silicones perform better than UV curing acrylates, which perform better than epoxies.

The problem of ice build-up in an engine or on the leading edges of a plane is a significant problem in the aircraft industry. Ice build up can affect many aspects of flying such as lift, drag, and thrust. Under the direction of Pratt & Whitney in 2004, the Department of the...

The problem of ice build-up in an engine or on the leading edges of a plane is a significant problem in the aircraft industry. Ice build up can affect many aspects of flying such as lift, drag, and thrust. Under the direction of Pratt & Whitney in 2004, the Department of the Army, Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory (CRREL) in Hanover, NH, U.S, performed adhesion strength tests designed to measure the adhesion strength of ice to several different commercially available ice-phobic coatings. The results show that the silicone material, R-2180, dropped the adhesion strength by a factor of 40 over bare steel and aluminum surfaces. These results were the lowest mean failure stress that CRREL has ever seen at 37 kPa while Teflon was previously the lowest tested value measured at 238 kPa.

Reworking electronic packages is an integral process related to diagnostics and salvaging valuable materials. It is a meticulous and time-consuming procedure that requires some knowledge of the package material composition to determine compatible cleaning solutions and processes. Silicone adhesives are being used more frequently due to their ability to minimize shear stress during temperature...

Reworking electronic packages is an integral process related to diagnostics and salvaging valuable materials. It is a meticulous and time-consuming procedure that requires some knowledge of the package material composition to determine compatible cleaning solutions and processes. Silicone adhesives are being used more frequently due to their ability to minimize shear stress during temperature cycling. A common method for removing silicone adhesive is by swelling in solvent and removing by mechanical methods taking care not to damage fragile materials and leave minimal residue. Silicone digesters (emulsifiers) are another means of removing cured silicone. They are comprised of weak acids or bases and remove silicone by breaking the siloxane bonds that make up the polymer matrix. They are able to penetrate into areas that are difficult, or impossible to reach, greatly reducing the risk of causing damage due to mechanical removal. The purpose of this study is to evaluate the rate of silicone removal by solvents and silicone digesters on silicones bonded to copper and aluminum. The removal rate was determined by developing a rating system based on time intervals where silicone was observed to delaminate or dissolve. Silicone adhesives and Thermal Interface Materials (TIMs) were used in the evaluation of two commonly used solvents and two commercially available silicone digesters. Copper and aluminum panels were evaluated by using a ~ 0.5 mm thick layer of silicone to bond 2 panels together. The samples were placed in cleaning solution for 24 hours at 40 degree Celsius and evaluated at specific intervals for any changes in appearance of silicone. Based on the performance of combinations of silicone, substrate and cleaner, the engineer can chose which method is best for reworking based on their own assembly configuration and materials.