Surfaces

From traditional Hot Air Leveling (HAL) to a wide variety of lead-free PCB surfaces, such as chemically Ni / Au, chemically tin, HAL lead-free and OSP coating to carbon printing – we have the right surface technology for every imaginable application.

Hot-tinned surface

Hot Air Leveling (HAL) / Leading

Widely used surface (in the leaded version) for printed circuit board technology.
Since December 2004 also in lead-free design, based on a tin-copper-nickel alloy.

Advantages
— excellent soldering properties/multi-solderable
— optimum edge protection
— low cost
— long shelf life

Disadvantages
— irregular tinning on SMD pads
— strong tin accumulation at fine pitch

Conclusion
Only conditionally usable with fine pitch printed circuit boards.

Gold surface

In printed circuit board technology, different gold surfaces are used for different applications. Here one distinguishes mainly between:

chemical nickel / gold surface
Application: Aluminum wire bonding and / or multiple soldering with flat pad surface.

Reductive gold surface
Application: Gold wire bonding (single case application)

galvanic nickel / hard gold surface
Application: mechanical contact (wear resistance) with simultaneous solderability.

galvanic nickel / bondgold surface
Application: Gold wire bonding (main application)

In the following list, the gold surfaces mentioned above are to be assigned to the typical fields of application. More detailed information about advantages, properties, etc. can be found in the respective subtopics. Of course, an overlap of application areas can not be ruled out and is required for special applications.

Chemically nickel / gold surface

Universal surface for printed circuit board technology.

Advantages:
— excellent soldering and bonding properties (aluminum wire bonding)
— flat pad surface
— uniform layer thicknesses
— optimum edge protection

Characteristics:
Nickel:
Nickel / phosphorus with 6 – 9% phosphorus
Hardness: 550 HV = 48 Rockwell
Density: 7.9 g / cm²
Melting point: 890 ° C
Specific resistance: 75 μΩ / cm
Thermal expansion coefficient: 13.8 μm / ° C
Corrosion resistance: approx. 250 h according to ASTM B117
suitable according to MIL-C-26074 E and AM52404A

Gold:
Fine gold: 99.99%
Hardness 60-80 HV
suitable according to MIL-G-45204 B Amendment 2, type III
Chemically nickel / palladium / gold

Chemically nickel / palladium / gold

Advantages:
— excellent soldering and bonding properties (gold wire bonding)
— flat pad surface
— uniform layer thicknesses
— optimum edge protection

Reductive gold surface

Surface for printed circuit board technology for gold wire bonding in the chemical process.

The chemical bond gold surface is used as the galvanic process (see also galvanic bond gold) for gold wire bonding. Here, the fine gold layer is deposited in the chemical thick-film late gold process. The layer thickness is significantly lower compared to gold wire bonding in the galvanic process. A process security of the bonding process is a prerequisite here. It is advantageous that a selective application of the gold layer is possible by the chemical method.

Characteristics:
Special suitability for HF printed circuit boards

Nickel:
Nickel / phosphorus with 7 – 10% phosphorus
Hardness: 550 HV = 48 Rockwell
Density: 7.9 g / cm²

Gold:
Fine gold: 99.99%
Hardness 50-60 HV

Galvanic nickel / hard gold surface

Surface for printed circuit board technology with high wear resistance.

The galvanic hard gold surface is used mainly where a high wear resistance and in additional good electrical properties with good corrosion resistance are required (sliding contacts / connector strips / test points for frequent contacting / etc.). Here, the hard gold layer of a gold / cobalt alloy with about 0.2% Co has proven. As a diffusion barrier between copper and gold, nickel is used in a layer thickness of > 3 microns.

Characteristics:
Nickel:
Chloride-free nickel sulfamate
low internal tension
high ductility
good soldering properties

Gold:
Gold / cobalt with 0.2% Co
Hardness 160-180 HV
Contact resistance 0.3 milliohms
high corrosion resistance
excellent abrasion resistance
low internal tension
specified according to MIL spec. G-45204 B Amendment 2 Type 1
Grade C-DTD 938

Galvanic nickel / bond gold surface

Surface for printed circuit board technology for gold-beam bonding.

The galvanic bond gold surface is considered the standard surface for gold wire bonding. Here, the fine gold layer is deposited by electroplating. The layer thickness is significantly higher than the gold wire bonding with Dickschichtsudgold (see also reductive gold). This brings a simplification of the bonding process. The galvanic process, however, makes selective application difficult under certain circumstances, since an electrical connection is necessary. An an alternative to the selective method, a complete gold plating of the PCB is possible. Here, however, the cost factor has to be considered.

Characteristics:
Nickel:
Chloride-free nickel sulfamate
low internal tension
high ductility
good soldering properties

Gold:
Fine gold: 99.99%
Hardness 60-80 HV
suitable according to MIL-G-45204 B Amendment 2, type III

Chemical tin surface

Universal surface for printed circuit board technology.

Advantages:
— excellent soldering properties or Mehrfachlötbarkeit
— flat pad surface (comparable to chem. Ni / Au)
— uniform layer thicknesses
— optimum edge protection
— low cost in the series

Disadvantages:
— sensitive surface
— Lower storage life compared to HAL surface

Layout requirements:
To ensure that a clean, residue-free finish is created, you must
everything at chem. Sn surface all vias are opened on both sides.

Organic surface – OSP

Organic surface for printed circuit board technology.

The process based on the copper imidazole chemistry separates controlled from a plane, multi-solderable 0.2 to 0.5 micron thick organometallic copper layer. This is transparent and makes the copper look dull. The ENTEK layer is selectively deposited on the copper.

Advantages:
— flat surface
— good soldering properties or Mehrfachlötbarkeit
— no thermal stress during coating
— low cost in the series

Disadvantage:
— sensitive surface

Solder resist

At ELEKONTA Marek the photoimageable solder resist Huntsmann Probimer 65 HF is used. This is applied by curtain coating.

Characteristics:
— High resolution of fine details
— High resistance to chemical nickel / gold and tin processes
— Non-flammability level according to UL: UL 94 V-0
— good conductor edge coverage

Carbon print

Surface for printed circuit board technology for special applications. e.g.:
— electromechanical keyboards
— Membrane keyboards for computers
— Switch contacts
— Shielding surfaces
— etc.

The carbon-conductive ink is a screen-printing varnish, which is enriched with a special carbon black and a special type of graphite and thus has a very good electrical conductivity. It is well-resistant in the hot-air leveling process (HAL) and in the soldering process and has almost no change in resistance after hot-dip tinning. Due to its very high abrasion resistance, contact points can be printed in which up to 25,000,000 contacts are possible.

Characteristics:
Resistance to soldering tin 10 sec. At 260 ° C
Sheet resistance / cm²: 20-30 Ω