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Final finish for PCB

Final finish for PCB   /  PCB production   /  Main

Final finish for PCB

To save good solderability of PCBs, flatness of the surface, solid montage of electronic components and solder connections of PCB it is necessary to protect cooper pads with final finish. There could be different final finishes applied on one PCB, depending on the purpose of the elements draw. It is done to provide with quality and solidity. It is also common to use the same final finish all over the PCB, it is done in case when the simplification of the manufacturing process is required.


We can offer you the optimal chose of final finish of one, two, maximum three variants (in special cases) for one title of PCB, satisfactory to all: price, solder quality and solidity requirements.




Hot Air Solder Leveling (HASL)

Thickness, um: 15-25

Hot Air Solder Leveling is a method of immersion of the panel to the bath with solder for a certain time and then leveling with hot air jet after it has been raised.

Advantages

  • HASL is one of the most wide spread and popular among final finish methods, consequently the technology of HASL is well known and developed good.
  • The strength of solder joint
  • Sustainable to numerous soldering cycles

Disadvantages

  • Significantly low pad flatness
  • Contains lead, not friendly for the environment and labor.
  • Difficult to implement for PCB with significant ratio circuit thickness vs hole diameter.
  • Significant thermal impact of the HASL process can lead to circuit distorting and is stressful to interlaminar connections.
  • It is not recommended to use HASL for PCBs with fine pitch components as it can lead to contact pads closure.
  • Uneven thickness of the coating over the contact pad.

Electroless Nickel - Immersion Gold (ENIG)

Autotech (Germany)

Thickness, um: 3-5,0 Ni; 0,06-0,1 Au


Immersion Gold is a thin gold film, applied over Nickel coating, which prevents the diffusion of gold and cooper . Gold coating provides with good soldering and protects Nickel interlayer, from oxidation.


Advantages:

  • Flat surface, even thickness of the coating.
  • Suitable for the fine pitch components
  • Doesn't influence the size of the plating holes.
  • Stands multiple thermal cycling
  • Suitable for brush and push-pull connectors.

Disadvantages:

  • The solderability significantly depends on the right chose of rectifier, flux and soldering options.
  • The storage of PCB with Gold Immersion requires vacuum packing and dry conditions.
  • PCBs contain Nickel, which is toxic
  • Not suitable for high - rate signals.
  • Possible defects like black pads
  • Gap limitation

Assembly recommendations....


Immersion Tin - ISn

Autotech (Germany)

Thickness, um: 0,8-1,2 Sn


It is a chemical coating, which provides good flatness of PCB and is suitable for all types of soldering in difference with ENIG. The application process is very common to Immersion Gold application.

Immersion Tin- Isn saves good soldering features of the PCB even after a long time of storage. It is provided by implementation of additional organometalic layer as a barrier between cooper pads and Tin The organometalic layer prevents the diffusion of cooper and Tin, intermetallic and Tin recrystallization processes. As the thickness of the coating is small crystallization of Tin is impossible in this case.


Advantages:

  • High solderability
  • The flat coating surface enables to apply fine pitch components
  • Suits for connection of printed contacts with PCB by Press Fit method.
  • Good for microwave PCBs (doesn't contain Nickel)
  • Does not influence the size of the plating holes.

Disadvantages:

  • PCB needs careful handling
  • Requires vacuum packing and dry conditions.
  • Is not suitable for keyboards and touchpads.

Assembly recommendations...


Gold Fingers

Thickness, um: 5 -6 Ni; 1,5 3 Au

The size of the coating: 300x50 mm

Electrolytic plating of printed contacts on Nickel layer. It is applied by electrolytic method of copper deposition on printed contacts and could be used together with another coating on one PCB. It is basically used for edge board contacts and lamels, is suitable for keyboards and touchpads manufacturing as well.


Advantages:

  • High toughness to mechanical injury, sustainable to negative environment impact and rub.
  • It is indispensable in case of durable contacts.
  • The thickness of the coating can be increased in several times.

Disadvantages:

  • High pricing
  • Only for printed contacts.
  • PCB size limitation

Carbon coating for contact fields in keyboards (NEW!)

This type of coating is applied in certain places on the circuit as a contact pad for keyboards. The carbon coating has good conductivity, doesn't oxidize and is wear resistant.

Solder masks, used in PCB production

Solder mask is a layer of tough material which protects conductors from solder and flux interaction while soldering, as well as from overheating. The mask covers conductors, but leave pads and printing contacts open. The method of solder mask application is photoimaging- the process of transmission an original image by phototool on the surface of the PCB material and than clear areas are exposed to radiation and polymerised, while solder pads stay protected, and mask is easily removed from the surface after manifestation. Usually the mask covers cooper layer, consequently, before solder mask is applied, the protective tin layer is removed, as it can deform under the impact of heating while soldering.

PSR-4000 H85 (TAIYO INK Japan)

- green color, Liquid Photoimageable Solder Masks, heat resisting, thickness: 15-30 um, TAIYO INK.

Is recommended by: NASA, IBM, Compaq, Lucent, Apple, AT&T, General Electric, Honeywell, General Motors, Ford, Daimler-Chrysler, Motorola, Intel, Micron, Ericsson, Thomson, Visteon, Alcatel, Sony, ABB, Nokia, Bosch, Epson, Airbus, Philips, Siemens, HP, Samsung, LG, NEC, Matsushita(Panasonic), Toshiba, Fujitsu, Mitsubishi, Hitachi, Toyota, Honda, Nissan and others.

IMAGECURE XV-501 (Coates Electrografics Ltd GB)

XV501T-4 is the current standard LPISM range it offers a high level of performance, improved track encapsulation and wide process windows. With process optimization T4 formulations are suitable for Ni/Au processing and HDI PCBs. Is available for all application methods.

DUNAMASK KM (Dunachem Germany)

dry film mask, thickness 75 um, provides tenting of through-holes, high- adhesive mask.

Rambler's Top100

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