smt概要(文件)
【正文】 g OperationnJoint shapenLayout of the conductor patternnProcess parametersnMaterials used381Effect of Flux on Wetting391SolderabilityThe ability of a material to be wetted with solder, the formation of a uniform, smooth, unbroken, adherent coat of solder on the base metal. n Wettabilityn Resistance to soldering heatn Resistance of metallisation to dissolution401Intermetallic Compound411Solder Paste Storage Handling Considerationsu Stabilize paste to room temperature after refrigeration for a least 58 hours prior to useWhy? If paste is not returned to room temperature the viscosity will be higher than specification and stencilling will be poor. Water condensation inside the paste will occur.421Solder Paste Storage Handling Considerationsu Stir for 30 seconds, 2 revolutions per second with appropriate plastic spatula before useWhy? Some settling (flux separation) can occur, gentle stirring with plastic spatula (to avoid plastic jar scrapings) can only help.431Solder Paste Storage Handling Considerationsu Discard any paste remaining on the stencil at day’s end and never mix fresh and used paste together in a same jar.Why? Paste will lose some solvent during use resulting in higher viscosity。相反如印刷壓力不足，也無法達(dá)到良好印刷效果，可能會造成漏印虛印等等現(xiàn)象。m261關(guān)於印刷速度關(guān)於印刷速度 (Printer speed) 印刷速度如太快，會發(fā)生虛印、漏印或錫膏量不足 (錫膏印刷時下降未完全 )。 ，錫膏表面產(chǎn)生硬塊，將表面硬塊除去方可使用。
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