When do you pre - tin MOS devices leads ?

• A. During testing
• B. Before final assembly
• C. Not at all
• D. After final assembly

Answer: (B)

Pre-tinning MOS device leads is done to ensure a solderable, oxide-free surface for reliable joints during assembly. By applying a tin coating to the leads beforehand, the solder wets the leads consistently in the later mounting process (reflow or wave soldering), producing a solid fillet and reducing the chance of cold joints or poor wetting. This preparation helps prevent oxidation on the lead surfaces and makes the joining process smoother and more repeatable. If you waited until testing or after final assembly, you wouldn’t have the leads prepared for a quality solder joint, and you could risk damage to components or weaker connections. So, the proper time to pre-tin is before final assembly.