What is Immersion Tin?

Immersion Tin is a method using a chemical process to apply a very thin tin layer over the copper layer. This method is a lead-free alternative that makes a consistently flat tin surface that solders well and is cost-efficient. This tin layer’s appearance is usually mostly white, so it is also commonly referred to as White Tin and is applied to the copper using an electroless chemical bath. This tin surface finish can protect the copper surface underneath from oxidation throughout the PCB’s intended shelf life.

However, one problematic aspect of this finish is the strong affinity of tin and copper for one another, which allows the diffusion of one metal into another. This process can cause the formation of “tin whiskers”, which are small strands of diffuse tin that can cause shorts and reduce the quality of solder joints, negatively impacting the shelf life and the performance of the PCB.See below figure 1

  Figure 1: Example of an Immersion Tin Surface Finish

Pros

• Lead-free

• High Reliability 

• Flat Surface/Planar 

• Cost-Effective 

• Can Substitute for Reflowed Solder

• Top Choice for Press Fit Pin Insertion

• Re-workable

Cons

• Not Good for PTH 

• Process Uses Thiourea, a Known Carcinogen 

• Not Good for Multiple Reflow/Assembly Processes

• Tin Whiskers

• Could Damage Solder Mask 

• Easy to Cause Handling Damage

• Difficult to Measure Thickness 
  
  Introduction for the surface choices
  Back to the Technology Data