SMT step by step―Step 3: Solder Materials

摘要

The fundamental rule of soldering is unchanged — create a bond using flux to remove oxides and prepare surfaces to be joined with a low-melting alloy. Lead-free soldering principles also are the same as leaded; however, the physical properties of these solders are different — wetting behavior is slower and the cosmetics sometimes differ. Achieving good solder joints using lead-free alloys has required manufacturers to revisit each process for optimization. In addition to higher heat needed to melt some lead-free solders, different fluxes must be used to reduce surface tension to promote good spread and wick-ing. Lead-free solder joint cosmetics also differ slightly from leaded, requiring training to recognize the difference between an acceptable joint and a poor one.