Encapsulant electrical performance

Of all the commercially available organic and inorganic polymeric materials, RTV silicone elastomer has proved to he one of the most effective encapsulants used for mechanical and moisture protection of the Integrated Circuitry (1C) devices. A general overview of the RTV silicone elastomer and its commercial preparation and cure mechanism are described. Improved electrical performance of the RTV silicone encapsulant, by immobilizing the contaminant ions, such as Na, K" , Cl , with the addition of the heterocyclic poly-ethers as the contaminant ion scavengers seems to have a potential application as the contaminant ionic migration preventor in the electronic applications. 

The electrical performance of the encapsulant is greatly dependent on its purity. Ionic impurities, such as sodium, potassium and chlorides, are harmful contaminants in the encapsulant. It has long been shown that ionic materials. 

Encapsulating available knowledge into parametric models for electrical performance at radio frequencies (RF) enables the designer to predict insertion loss, return loss (reflection), and insertion phase and delay of the MEMS switch without time-consuming full-wave analysis in the same environment as used for the initial electromechanical analysis. 

Properties of nanofillers recently developed nano materials are reported to display greater mechanical strength, greater thermal conductivity and improved electrical performance when compared to materials of normal particle sizes. Nano dimensional materials are being studied as fillers in polymer matrices in a variety of formulations for electrically conductive adhesives, thermally conductive adhesives, encapsulants, printed circuit boards, coatings, catalysts, underfills for flip-chip-attached devices and wafer-level connections. ... 

The abiHty of a given material to perform as an electronic embedding encapsulant depends largely on its properties. Ultrapure chemical properties with a low level of mobile ions such as sodium, potassium, and chloride are essential. Furthermore, the material s electrical, mechanical, and rheological properties are critical. 

Figure 5. Triple-track resistor electrical testing performance of crown ethers in commercial RTV silicon encapsulants. Conditions bias, 180 V relative humidity, 96% temperature, 100°C.

High performance silicone gels have been shown to have excellent electrical characteristics. With their superior jelly-like (near zero modulus) intrinsically soft, physical property and ultra-high chemical purity, silicone gels are becoming very attractive encapsulants. They are chosen to... 

Figure 4 shows the performance of encapsulated devices under the standard bias pressure cooker device test. The conditions of this test are as follows 100% relative humidity, 15 psig, 250°F, and electrical bias. In this test, the encapsulant based on stable bromine CEN took more than 1000 hours to achieve 50% cumulative failure while the encapsulant based on the standard high purity resins took about 700 hours. 

Figure 6 shows the performance of encapsulated devices under the highly accelerated stress test which utilizes the following conditions 145°C, 85% relative humidity, 37 psig, and electrical bias. The bias on this test is cycled specifically, the bias is initially off to allow for full moisture penetration and then turned on. These cycles are repeated throughout the test. The stable bromine CEN compound took 2500 hours to reach 50% failure rate, compared to the standard resin compound at 1900 hours. 

The electrical properties of polymers are important in many applications [1]. The most widespread electrical application of polymers is the insulation of cables. In recent years, high-performance polymers have become important in the electronics industry as encapsulants for electronic components, as interlayer dielectrics, and as printed wiring board materials. The dielectric constant (or permittivity) and the dissipation factor (or power factor or electrical loss tangent) tan 8, which are dimensionless quantities, are the key electrical properties. 

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