Printed circuit board surface finish

Printed circuit board surface finish

The circuit board surface is responsible for raising the wetting ability of the contact areas for soldering; non-chemical surfaces serve simultaneously as protection against oxidation of the covered copper and improve shelf life characteristics. 

The circuit board surfaces vary in shelf life, typical application field and price, but are normally specified by the process, product or desired location for the application.

Available surfaces

Surface
Hal SnPb										>5µm	ca.12 months	5
HAL lead-free										>5µm	ca. 12 months	5
Chemical tin										>1µm	ca. 6 months	5
Chemical silver										0.2 - 0.3µm	ca. 12 Monate	5
Chemical gold ENIG										3-6µm Ni 0.05-0.1µm Au	ca. 12 months	5
ENEPIG										3-8µm Ni 0.05-0.15µm Pd 0.05-0.1µm Au	ca. 12 months	-
Galvanic softgold										4 - 6µm Ni >1µm Au	ca. 12 months	-
Galvanic hardgold										4 - 6µm Ni 0.1 - 2µm* Au	ca. 12 months on request	-

HAL SnPb

HAL SnPb (lead-tin) is nowadays allowed only in certain technology fields such as medicine and space travel. HAL is suitable for standard SMD, but shows weaknesses in fine pitch applications. A chemical surface is preferable for finepitch.

• Advantages:

• Good solderability               

   

• 
  

• Good reflow properties

Disadvantages:

• Pads are non-planar

• Not RoHS-compliant

   

Chemical tin

The surface chemical tin is for manufacturing reasons rarely requested any more! Due to the rapid oxidation of the copper, the shelf life is highly dependent on temperature and packaging. Fingerprints on the surface should be avoided at all.

Advantages:

• Absolutely flat

• Good for fine pitch

• Good for SMD

• Good for press-fit

Disadvantages:

• Extra charge

• Critical manufacturing process

• Faster oxidation, thus:

• Limited storability