Surface Finishes types for Soldering
Since the invention of the printed circuit board, there has been a parallel interest in developing a means of protecting the copper surfaces from hostile environment and in maintaining solder ability of those surfaces during storage and throughout the life of the assembly.
HASL - Hot Air Solder Leveling - with eutectic tin/lead is still the number one in number of square feet PCB's produced, but a number of newer surface protections exists to day.
GPV(Su Zhou) offers the following surface finishes:
Hot Air Solder Leveling with eutectic tin/lead, 63% tin and 37% lead in a vertical process. It is suitable for wave soldering and SMT reflow of low and medium pitch components.
Hot Air Solder Leveling (Leadfree) is a new surface treatment, exclude harmful element Pb, It is suitable for wave soldering and SMT reflow of low and medium pitch components.
Electroless Nickel/gold, this process deposits a uniform electroless nickel/gold coating over exposed copper surfaces as well as in plated through holes. The thickness of the nickel layer is minimum 4 micron, the thickness of the gold layer is maximum 0.2 micron. The flatness is excellent.
It is suitable for wave soldering, SMT reflow of fine pitch components and wirebonding. With careful design it is also suitable as a contacting surface.
Immersion tin, this process deposits a uniform pure tin coating with a nominal thickness of minimum 1.0 micron, the flatness is excellent and it is suitable for wave soldering and SMT reflow of fine pitch components. Immersion tin is not suitable as a contacting surface or as a bonding surface.
A comparison of attributes for different surface finishes are shown in the table below.
|
Finish Attribute |
HASL |
Immersion tin |
Electroless |
Organic solder preserv. |
Organic |
|
Fine line / Fine pitch |
0 |
+ |
+ |
+ |
+ |
|
Multiple solder processes |
+ |
+ |
+ |
0 |
+ |