What is OSP?

Purpose of OSP

Organic Solderability Preservative (OSP): OSP is a layer of organic membrane growing on a clean bare copper surface to protect the copper surface from rusting (oxidation or vulcanization) in normal environments. However, this protecting film must be removed easily and quickly by fluxes at high temperatures in the subsequent soldering process, so that the exposed clean copper surface can bond with the molten tin solder to form a firm soldered dot. This organic film that can protect the copper against rusting is called Organic Solderability Preservative (OSP).

  • Function of OSP:
    Heat resistance

Development history of OSP

1st generation: Brenzotriazole (BTA).
2nd generation: Imidazoles (IA).
3rd generation: Benzimidazoles (BIA).
4th generation: Substituted Benzimidazoles (SBA).
5th generation: Aryl Phonylimidazoles for lead-free soldering.

Features of the latest generation:

  1. Non-stick effect on gold surface
  2. Pyrolysis temperature up to 354.7 °C and resistant enough for 3 lead-free soldering operations
  3. Pushed away easily by no-clean fluxes
  4. Thickness reduced up to 0.2–0.3μm
  5. Testable after OSP

Note: Lead-free soldering requires higher temperature (higher than 30 °C on average) and longer operation time (fusion welding time 60 sec at 200 °C or above; for wave soldering, 60 sec at the heat absorption phase of 200 °C or higher up to the peak temperature of 265 °C). The current OSP is resistant enough for 3 lead-free soldering operations.

Type of OSP

1-3-1. Gold resistance series

This is suitable for gold finger (G/F) and selective Ni/Au + OSP board. Special attention must be paid to the control of the copper ions in the OSP bath solution. The disadvantage is that the a deep etching is formed on the cooper surface during the pre-dip process, leading to a significant color difference on the surface of the film.

1-3-2. Non-gold resistance series

The non-gold resistance series is used in normal situations to avoid color difference or other adverse reactions brought about by the bad copper surface material coming from the previous station.

1-3-3. Electrically testable after OSP

OSP is an organic membrane without resistance and does not affect the electrical test.

1-3-4. Electrically untestable after OSP

OSP is an organic membrane with resistance. The value of the resistance affects the normal conduction between the test device and copper surface.

Comparison of different surface treatment process propertiesosp 2

Comparison of OSP advantages and disadvantagesosp 3

Physical and chemical properties of OSP and operation parameters by brand (1):osp 4

Physical and chemical properties of OSP and operation parameters by brand (2):osp 5

OSP copper/gold board operation conditions by brand:osp 1 1

OSP heat resistance by brand:osp 6


1.As the development of the technology is constantly evolving, the newly developed OSP chemical agents (made in Taiwan and China) have reached a world-class level and the market has become a “red ocean” of competition.

2.The aforementioned operation and control parameters of the solutions may vary slightly depending on the requirements and equipment limitations of the customer.

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