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What PCB surface finishes are offered in Seeed Fusion?

Seeed Fusion's standard PCB service offers four surface finish options from the popular HASL to high-quality ENIG finishes to suit different applications. A surface finish is applied to the exposed copper pads to protect them and prevent oxidation, which would strongly inhibit the contact pad's ability to bond with molten solder.

HASL - Hot Air Solder Levelling

For HASL finishes, the boards are dipped in a bath of molten solder and then passed through a conveyor of hot air knives that brush the excess solder off. Essentially, the copper pads are pre-tinned with the thinnest layer of solder possible, and the tinning protects the bare copper underneath. This gives the boards good shelf-life and the existing layer of solder makes the molten joints much easier to join. The HASL surface finish is the simplest and most common surface finish and is sufficient for most projects. However, it is not ideal for fine-pitch components since the thin layer of solder still leaves a rounded surface and the components will not lie completely flat against the surface of the pad. 

A lead-free variant is also available for RoHS compliance products. Please note that higher soldering temperatures are required for lead-free solder.

ENIG - Electroless Nickel / Immersion Gold

In the ENIG plating process, the copper pads are protected by a coating of nickel, and then the nickel is protected with a fine layer of gold particles. This offers superior corrosion resistance compared to HASL due to the high corrosion resistance of gold. In addition, the excellent surface planarity of the nickel/gold finish allows components to be soldered flat onto the pad, making it ideal for BGA pads and other fine-pitch components. The disadvantages include the higher cost of the gold solution and soldering is not as easy compared to HASL since there is no pre-tinned surface. Solderability is still good, however.

Hard Gold

Similar to ENIG, the pads are plated with nickel but then with a much thicker layer of gold. Hard gold is common for gold fingers or other hard wear areas which require durability and excellent resistance to corrosion. Like ENIG, solderability is poor and the cost is even higher since a thicker layer of gold is applied. If you select the Hard Gold option, we will plate the entire board with Hard Gold. For small batches and prototyping orders, a different plating process is used compared to large batch processing lines. With this process, it is much more difficult and labor intensive to apply more than one surface finish on the boards, therefore, dual surface finish boards are currently not available at Seeed Fusion.

eg.The default thickness of gold on the finished board is 1-2mil. If you have other request for the thickness of the gold on finished board.Please indicate the request in the file.

The following options are only available in the Seeed Fusion Advanced PCB service.

OSP - Organic Solderability Preservative

A thin layer of a water-soluble organic compound is applied to the surface of the boards, which then selectively adheres to the copper surfaces, forming an almost undetectable protective layer. This makes it ideal for fine-pitched devices but the shelf life is relatively short - up to one year, so it is more suited to batch assembly rather than prototyping. It is also clear in color, making it difficult to inspect the coverage of the compound. It is the most environmentally friendly of all the available finishes.

Immersion Tin

Tin is deposited onto the surface of the copper via a displacement reaction which removes some of the surface copper in the process. The resulting finish has excellent planarity and the reliability is comparable to ENIG. The thickness of the tin layer is also much easier to control, but the process involves the use of a carcinogen and the boards must be handled carefully to avoid contamination.

Immersion Silver

Similar to immersion tin, immersion silver produces exceptionally flat surfaces, has great solderability and can serve as an ENIG alternative but it also has a poor shelf life and does not respond well to handling. The immersion silver process however, does not use highly toxic chemicals and does not affect the final diameter of plated holes. Due to a high friction coefficient, immersion silver surface finishes are not suited for pin insertion or press-fit machines.

Hard Gold + ENIG

A process in which only some pads are plated in Hard Gold and the rest are plated using the ENIG surface finish. Great for boards requiring Gold Fingers.

Currently, no longer available at most Chinese small batch/prototyping manufacturers due to the extra labor involved. Please inquire for large batch processing.

Last modified 2018/08/11

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