Surface Treatment – PCB DFM 12

12.1 Hot Air Solder Leveling (HASL)

12.1.1 Process Requirements

[103] The PCB is covered with molten tin-silver alloy and the excess is blown off using hot air. The
resulting alloy coating on the exposed copper surfaces must be between 1 m to 25 m.

12.1.2 Range of Applications

[104] Using HASL, it is difficult to control the thickness of the coating and preserve the precise shape of
the copper pads. It is not recommended for PCBs with fine pitch components since the copper pads of fine
pitch components typically need to be flatter. In addition, the thermal shock of the HASL process may cause
the PCB to warp. Therefore ultra-thin PCBs with a thickness of less than 0.7 mm are not recommended to
undergo this type of surface treatment.

12.2.1 Process Requirements

[105] Electroless Nickel Immersion Gold (ENIG) is a surface treatment involving plating the copper pads
with nickel then immersion gold to help prevent it from oxidation. PCB copper metal surfaces treated with
ENIG must have a nickel coating thickness of 2.5 m-5.0 m, and the immersion gold (99.9% pure gold) layer
thickness must be 0.08 m-0.23 m.

12.2.2 Range of Applications

[106] Due to the resulting flat surface, this process is suitable for PCBs with fine pitch components.
12.2.3 Organic Solderability Preservatives (OSP)
[107] This process covers the exposed copper pads with a thin coat of an organic compound. Currently, the
only recommended organic formula is Enthone’s Entek Plus Cu-106A, which results in a thickness of
0.2 m-0.5 m. Because of the incredibly flat coating, it is especially popular with PCBs with fine pitch

Seeed Studio Fusion is a place to order custom PCB boards offering 4 kinds of surface finish including HASL, HASL Lead Free, ENIG, Hard Gold.

More Chapters:
1. Brief Introduction
2. Seeed Fusion PCB Specification
3. Panelization and Bridge Design
4. Component Layout Considerations
5. PCB Hole design
6. Solder Mask Design
7. Copper Trace Design
8. Silkscreen Design
9. PCB Lamination Structure
10. PCB Dimensions Specification
11. Fiducial Mark Design
13. Files for Manufacture Requirements
14. Appendix 

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August 2017