Finishing of the PCB is important and necessary for the soldering process. Finishing provide and increase the wettability in the assembly process, also serve as protection against oxidation of the copper and prolong the shelf life or useful life of the circuit.
There are different types of finishing, all available in CIPSA:
Immersion Tin: Pure tin deposition by dipping a thickness of between 1.0 µm to 1.3 µm. Finishing Lead Free, It complies with RoHS normative. It can be stored up to 1 year. Excellent flatness, recommended for SMD complex, Fine Pitch BGA, PressFit and Multisolder (up to 3). The main advantage is that can be ‘reworked’ or ‘refreshed’ due to oxidation or storage expiration. The problem it has is the growth of the intermetallic (IMC) during storage, which requires giving thicknesses greater than 1 µm of Tin. It is the most generalized finishing with the minimum risk assumed.
Immersion silver plating: Immersion silver deposition of a thickness between 0.15 µm to 0.35 µm. Finishing Lead Free, It complies with RoHS normative. It can be stored up to 1 year. Excellent flatness, recommended for SMD complex, Fine Pitch BGA, PressFit and Multisolder (up to 3). The advantage is the low thermal aggression (‘thermal stress’) during the production process and excellent resistance to external agents such as temperature and humidity. The disadvantage is the difficulty that has reprocessing.
HAL Sn/Pb: It is done for those applications that are still exempt from the RoHS Directive. The deposition thickness is irregular, 1 µm to 10 µm. Not recommended for SMD soldering of some complexity for its lack of flatness and uniformity. The advantage is their long storage (24 months) and reducing the cost of tin in the soldering process.
HAL-LF: Same as above, but without Lead. It complies with RoHS normative. The deposition thickness is irregular, 1 µm to 10 µm. Not recommended for SMD soldering of some complexity for its lack of flatness and uniformity. Its storage period is lower (approx. 18 months).
ENiG (Immersion Ni/Au): Electroless deposition of nickel on copper between 4-7 µm and Gold on nickel from 0.06 µm to 0.12 µm. Finishing Lead Free, it is RoHS compliant. Storage up to two years. Excellent flatness, recommended for multisolders (over than 3), for aluminium wire bonding, gold wire bonding, switching & spring contacts. The ‘only’ inconvenience is the highest cost.
Hard Gold: Plated deposition of nickel from 4 to 7 µm, and over, from 0.10 µm to 2.0 µm of gold.
OSP (Organic Copper Coating): Electroless deposition of a thin organic layer of solderable component no more than 0.15 microns. It complies with RoHS normative. Finishing with excellent flatness, recommended for 1 single soldering processes that will be performed immediately. The storage time is short (6 months).