1. Tin-lead hot air leveling
Application: The current application is limited to products exempted from the RoHS Directive and military products, such as communication products of the single board (Line card) and backplane (Back plane) for the device pin centre distance ≥ 0.5mm PCBA
Cost: Medium.
Compatibility with lead-free: not compatible, but can be used as a surface treatment for line cards for telecommunication products.
Shelf life: 12 months.
Solderability (wettability): High.
Disadvantages.
Not suitable for devices with pin centres <0.5mm, as they are prone to bridging.
Not suitable for use where high coplanarity is required, e.g. for medium to high pin count BGAs, as the HASL process has a large variation in plating thickness and poor pad to pad coplanarity.
Due to the relatively large relative thickness of the plating, the drilled hole diameter (DHS) must be compensated for to obtain the desired finished metallisation hole diameter (FHS), typically FHS = DHS - 4 to 6 mil.
Supplier resources: Medium, but with fewer customers using leaded processes, PCB manufacturers are gradually reducing HASL production lines and resources will become increasingly scarce.
2. Lead-free hot air leveling
Application: alternative to SnPb HASL, suitable for PCBA with device pin centre distance ≥0.5mm.
Cost: Medium to high.
Compatibility with Pb-free: compatible.
Shelf life: 12 months.
Solderability (wettability): high.
Disadvantages.
Not suitable for devices with pin centres <0.5mm apart, as they are prone to bridging.
Not suitable for use where high coplanarity is required, e.g. BGAs with medium to high pin counts have poor pad to pad coplanarity due to the relatively large variation in plating thickness in the HASL process.
Due to the relatively large relative thickness of the plating, the drilled hole diameter (DHS) must be compensated in order to obtain the desired finished metallisation hole diameter (FHS), typically FHS = DHS - 4 to 6 mil.
Due to the high peak surface finish temperatures, thermally stable dielectric materials must be used.
Supplier resources: currently limited, but will increase with the development of using lead-free processes.
3. Plain organic protective coatings
Applications: The most widely used surface treatment. Recommended for the surface treatment of fine pitch devices (<0.63mm) and devices with relatively high requirements for solder tray coplanarity due to its flat surface and high solder joint strength.
Cost: low.
Compatibility with lead-free: compatible.
Shelf life: 3 months.
Solderability (wettability): low.
Disadvantages.
Requires special processes in the PCB factory.
Not suitable for mixed assembly processes (cartridge components mixed with mounted components) for single boards.
Poor thermal stability. After the first reflow soldering, the rest of the soldering operation must be completed within the period specified by the OSP manufacturer (generally 24h).
Not very suitable for veneers with EMI ground areas, mounting holes, test pads. Also less suitable for veneers with crimp holes.
Supplier resources: more.
4. High temperature organic protective coating
Applications: Used as a replacement for OSP- -stand, suitable for more than 3 soldering operations. Recommended for installations with a large number of fine-pitch devices (<0.63mm) and for products with a high requirement for coplanarity.
Cost: low.
Compatibility with lead-free: compatible.
Shelf life: 3 months.
Solderability (wettability): low.
Disadvantages.
Requires special processes at the PCB factory.
After the initial reflow soldering, the rest of the soldering operation must be completed within the period specified by the OSP manufacturer. Usually required within 24h.
Less suitable for veneers with EMI ground areas, mounting holes, test pads. Also less suitable for veneers with crimp holes.
Supplier resources: more.
5. Nickel/gold plating (soldering)
Applications: mainly used for / non-soldering electroplated nickel and gold selective plating use.
Cost: High.
Compatibility with lead-free: compatible.
Shelf life: 12 months.
Solderability (wettability): High.
Disadvantages.
Risk of embrittlement of solder joints/soldering seams.
Features (wires, pads) have exposed copper on the sides and cannot be completely wrapped or covered.
Plating is completed prior to soldermask. Solder resist is applied directly to the gold side, therefore the strength of the adhesive surface finish of the resist layer will be somewhat compromised.
Supplier resources: Medium.
6. Non-soldering electroplated nickel/gold (hard gold)
Application: For use on gold fingers, rail mounting edges and other wear-resistant requirements.
Cost: Medium, but high when used as a selective plating.
Compatibility with lead-free: compatible.
Shelf life: 12 months.
Solderability (wettability): low.
Disadvantages: non-solderable.
Can be applied after a soldermask process, but this process may lead to soldermask peeling in fine pitch devices.
Supplier resources: Multiple.
