Silver Sintering Technology in Semiconductor Packaging
Due to its excellent electrical and thermal conductivity, Ag sintering is emerging as a proven and reliable bonding technology for high-power-density applications. This technology is particularly useful for IGBTs and MOSFETs, applications with wide band-gap materials, and devices that require lead-free bonding materials or high performance. First generation Ag sintering paste often requires pressure-assisted sintering and can only be sintered in air. Today Ag sintering products can be sintered in nitrogen atmosphere without pressure.
In comparison to electrically conductive adhesives and inks, silver particles used in Ag sintering pastes tend to be smaller in size, ranging from tens of nanometers to a few microns. Due to their higher surface areas, these finer Ag particles allow faster diffusion during sintering.
Ag sintering paste consists of Ag powders and a liquid carrier which evaporates during sintering, resulting in 100% silver content after sintering. This system tends to show consistency in high electrical and thermal conductivity, and high adhesion on Ag and Au surfaces. However it is harder to bond to copper and aluminum surfaces. The so-called semi-sintering die attach adhesives contain curable resins. While these materials can bond to copper and aluminum surfaces, their electrical and thermal conductivity tend to be inconsistent as the resins may prevent silver particles from sintering.
Though Ag sintering pastes tend to show high thermal conductivity, it is quite tricky to measure their thermal conductivity. Sample dimensions and preparation method, the atmosphere, pressure, and heating profile during sintering can greatly affect sample density after sintering. Therefore it is no surprise that the thermal conductivity numbers reported by different material suppliers can hardly be compared with each other.
After years of product development efforts, Yongoo has successfully developed Y-Bond S280 series of Ag sintering paste. These products are 100% Ag systems, can be sintered without pressure and some can be sintered in nitrogen atmosphere. After sintering, they demonstrate higher adhesion strengths than competitions.
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