The circuit board surface is responsible for raising the wetting ability of the contact areas for soldering; non-chemical surfaces serve simultaneously as protection against oxidation of the covered copper and improve shelf life characteristics.
The circuit board surfaces vary in shelf life, typical application field and price, but are normally specified by the process, product or desired location for the application.
| Surface |  RoHS-compliant |  Soldering |  Bonding aluminium wire |  Bonding gold wire |  BGA |  Flex-/Rigid-Flex |  Pressfit |  PCI contacts |  Sliding contact |  Thickness |  Shelf life |  Reflow Cycles | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Surface | Hal SnPb | RoHS-compliant | Soldering |  | Bonding aluminium wire | Bonding gold wire | BGA | Flex-/Rigid-Flex | Pressfit | | PCI contacts | Sliding contact | Thickness | >5µm | Shelf life | ca.12 months | Reflow Cycles | 5** | |||||||
| Surface | HAL lead-free | RoHS-compliant | | Soldering | | Bonding aluminium wire | Bonding gold wire | BGA | Flex-/Rigid-Flex | Pressfit | | PCI contacts | Sliding contact | Thickness | acc. to IPC-6012* | Shelf life | ca. 12 months | Reflow Cycles | 5** | ||||||
| Surface | Chemical tin | RoHS-compliant | | Soldering | | Bonding aluminium wire | Bonding gold wire | BGA | Flex-/Rigid-Flex | Pressfit | | PCI contacts | Sliding contact | Thickness | >1µm | Shelf life | ca. 6 months | Reflow Cycles | 5** | ||||||
| Surface | Chemical silver | RoHS-compliant | | Soldering | | Bonding aluminium wire | | Bonding gold wire | BGA | Flex-/Rigid-Flex | Pressfit | | PCI contacts | Sliding contact | Thickness | 0.2 - 0.3µm | Shelf life | ca. 12 Monate | Reflow Cycles | 5** | |||||
| Surface | Chemical gold ENIG | RoHS-compliant | | Soldering | | Bonding aluminium wire | | Bonding gold wire | BGA | | Flex-/Rigid-Flex | | Pressfit | | PCI contacts | Sliding contact | Thickness | 3-6µm Ni 0.05-0.1µm Au | Shelf life | ca. 12 months | Reflow Cycles | 5** | |||
| Surface | ENEPIG | RoHS-compliant | | Soldering | | Bonding aluminium wire | | Bonding gold wire | | BGA | | Flex-/Rigid-Flex | Pressfit | | PCI contacts | Sliding contact | Thickness | 3-8µm Ni 0.05-0.15µm Pd 0.05-0.1µm Au | Shelf life | ca. 12 months | Reflow Cycles | - | |||
| Surface | Galvanic softgold | RoHS-compliant | | Soldering | | Bonding aluminium wire | Bonding gold wire | | BGA | Flex-/Rigid-Flex | Pressfit | PCI contacts | Sliding contact | Thickness | 4 - 6µm Ni >1µm Au | Shelf life | ca. 12 months | Reflow Cycles | - | ||||||
| Surface | Galvanic hardgold | RoHS-compliant | | Soldering | Bonding aluminium wire | Bonding gold wire | BGA | Flex-/Rigid-Flex | Pressfit | PCI contacts | | Sliding contact | | Thickness | 4 - 6µm Ni 0.8 - 2µm Au | Shelf life | ca. 12 months on request | Reflow Cycles | - |
* IPC-6012: Fully covered and solderable | ** not reliable empirical values
HAL SnPb (lead-tin) is nowadays allowed only in certain technology fields such as medicine and space travel. HAL is suitable for standard SMD, but shows weaknesses in fine pitch applications. A chemical surface is preferable for finepitch (see also HAL vs. chemical gold).
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HAL (Hot Air Levelling) is a well-proven method to apply tin as circuit board surface. Every assembler should be able to process circuit boards with HAL surfaces without any problem. HAL is suitable for standard SMD, but exhibits some weaknesses for finepitch applications, for which a chemical surface should be preferred (see also HAL vs. immersion gold).
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The surface chemical tin is for manufacturing reasons rarely requested any more! Due to the rapid oxidation of the copper, the shelf life is highly dependent on temperature and packaging. Fingerprints on the surface should be avoided at all.
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This circuit board surface is very similar to chemical tin, with better properties for oxidation and contact applications. The surface is very flat and therefore suited very well for finepitch.
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Just as with chemical tin and chemical silver, chemical gold is an extremely flat circuit board surface, and has very good oxidation properties. It is perfectly suited for finepitch and bonding (aluminium wire) applications. Due to popular demand, Multi-CB can offer chemical gold in pooling service (cheaper price). Chemical gold is also called ENIG (Electroless Nickel Immersion Gold).
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ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) is extremely planar and has very good oxidation properties. It is ideally suited for soldering applications and aluminum wire bonding / gold wire bonding.
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