TIN PLATING : 

HOW TO INCREASE SOLDERABILITY SHELF LIFE ?


Normally we do tin plating for soldering and contact purpose .Here I am writing about tin plating on copper and copper alloys only . When we do soldering After tin plating , Soldering will be very nice . Then we assessed the tin plating part is good . Same parts we pack & supply or keep in store for some weeks or months . After that customer found that tin plated component got discolour and soldering not getting proper . Then they start blaming to platers for faulty tin plating . In this situation parts manufacturer and plater both will be in problem.

 When plater did the tin plating that time soldering was good but after some time soldering failed . It means soldering shelf life of components is very less .

REASONS OF PROBLEM 

 Normally this problem occur due to copper diffusion and  intermetallic layer formation between tin and copper , which can grow to reach the surface of tin coating and this  will reduce the solderability shelf life . 

NICKEL UNDERCOAT IS THE SOLUTION 

Copper diffusion and Intermetallic layer formation between tin and copper is very fast . To enhance the solderability shelf life of components nickel undercoat between copper and tin is must . Intermetallic layer formation between tin and nickel  is slow compare to tin and copper .

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TIN PLATING :

EFFECTS OF BRIGHTENERS & ADDITIVES 

When we do tin plating in sulphuric acid bath , we have to add brighteners and additives for bright finish otherwise we don't get brighteness and proper adhesion . Normally brighteners and additive constituent approximately 3.5 to 4 percent of plating bath . Brighteners and additives are organic chemicals and after  plating some layers of brighteners and additives will be present on the coated surface , this layer is not going to remove 100 % in the water rinse . To remove this layer we have to give alkaline dip, hot water etc  otherwise after some time light brownish or blackish film will be form on the coated surface or cause solderability problem .

                       



     TIN PLATING

Tin  plating  come maximum from electronics industry. In electronic industry Tin plating is more preferable because of its solderability  properties and costing of tin plating is less compare to  silver plating and  less hazardous compare to  tin/lead plating . Tin coating is non- toxic , ductile and corrosion resistant .

Tin plating have two types of finish in the terms of appearance :

 1. Matt  - Matt finish tin coating can get in alkaline tin plating solution .

 2. Bright - Bright finish tin coating can get in acid (sulphuric acid or Sulphonic acid ) base   bath along with brighteners and additives .

Conductivity of tin  =  9.17×10⁶           Siemens per metre

Tin  plating process :

1.  Pretreatment  process ( Depend on base metal like copper, aluminium, brass,steel etc)

2. Undercoat coating like copper , Nickel ( optional)

3. Tin plating

4. Passivation

Quality Control :

1. Physical appearance Inspection

2. Adhesion Test by Adhesive tape

3. Thickness test by thickness tester

4. Solderability test