smt培訓(xùn)資料05(參考版)
2025-02-27 06:34本頁面
【正文】 Reflow soldering for FinePitch Components Critical factors in reflowing soldering ? 1 The heat transfer from a heating source. ? 2. The heat absorption rate and uniformity by assembly. ? 3. The solderability of the metals to be joined. ? 4. The melting point of the solder. ? 5. The heat tolerance of the material on the assembly. ? 6. The flux chemistry and the cleanliness of the metals to joined. Dynamics of the Reflow Process ? Phase One Solvent Evaporation ? Phase Two Flux Activation (Oxide Reduction) ? Phase Three Solder Melt ? Phase Four Complete Solder Melt ? Phase Five Cool Down Temperature and time profile Tin/Lead solder oxide growth rates thickness vs time Increasing Flux Rate Probability of IC package crack Temperature and time profile The Heat Sources ? 1. Infrared (including IR and IR mixed with convection. ? 2. Vapor phase ? 3. Convection hot gas ? 4. Laser ? 5. Thermosonic ? Infrared reflow – The infrared heat transfer is done by emitting light from the infrared region of the spectrum. IR emission is that having wavelength of microns to 1000 microns – micron , short IR – micron , medium IR – longer than micron, long wave IR ? The IR emitter temperature determines the emitted wavelength of IR radiation ? The higher the temperature , the shorter the emitted wavelength. ? The temperature of the PCBA is a function of the absorbitivity of the assembly. ? The absorbitivity is IR wavelength and material mass dependent if
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