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Soldering surface coatings

Lead-free surface coatings
The following lead-free coatings for soldering surfaces are available:
HAL lead-free
Immersion Gold(Ni/Au)
Immersion Silver

Immersion Tin.
These coatings are RoHS compliant!

RoHS compliance

Comparison of lead-free soldering surface coatings

Available Coatings

HAL lead-free

Immersion Gold(Ni/Au)

Immersion. Tin

Topography
Layer thickness

convex *1
approx. 1-30µ *1

plane *2
approx. 4-6µNi;
0,1µ Au

plan *2
0,8-1,2µ *2

Shelf life influence

Surface corrosion
Diffusion zone growth

not critical
not critical *3

not critical
not critical *3

not critical
critical *3

Solderability / multiple soldering processes *4

1stsoldering process

good

good

good

Under O2 long term

good

good

critical

Under O2 short term

good

good

critical

Under N2 long term

good

good

good

Under N2 short term

good

good

good

Additional applications

Edge connectors

not suitable

limited suitability

limited suitability

Press-Fit Technology

limited suitability

limited suitability

suitable

Aluminium wire bonding

not suitable

suitable *5

not suitable

Keyboard application

not suitable

suitable

unknown


Available Coatings


HAL lead-free


chem. Ni/Au


chem. Tin

Special advantages

robust soldering
surface with solder
depot, good shelf life

universal plane
surface, good shelf
life

universal plane
surface

Special disadvantages

lack of surface
planarity, thus critical
for BGA and similar
pads, HAL causes
high thermal stress

failure risk of “black
pads”, high costs

formation of whiskers,
multiple soldering may
be difficult

BYSCO can recommend the following solutions:

(All evaluations and recom-mendations are based on today’s state of knowledge and are non-committal. The user is supposed to perform his own testing based on his specific conditions and requirements.)

For all PCBs where lack of surface planarity does not cause problems and the thermal stress caused by HAL is not critical.

For demanding SMD boards and / or special require-ments like bonding etc.

For demanding boards with SMD fine-pitch pat-terns, provided that soldering conditions are suitable.

General remarks concerning lead-free soldering surface coatings

1.

Physically deposited layers, e.g. HAL layers deposited by the application of liquid solder, have a significantly higher thickness, however, they are not plane.

2.

Chemically (i.e. currentless) deposited metal layers as e.g. Ni/Au, tin or silver, cannot be grown to any desired thickness due to the nature of the process which will come to a standstill once the noble metal has fully covered the ignoble copper. This process creates a plane surface which is identical to the topography of the underlying copper surface.

3.

Independent of the deposition method, generally a so-called diffusion layer is formed between two layers of different metals. This barrier layer is created by an exchange of atoms between the metals of different nobility. There will be a “mixing” of the base copper and the metal of the “ennobled” soldering surface.

The thickness of this diffusion layer depends on the type of metals involved as well as on the temperature conditions and the time for which the temperature conditions affect the layer system. Higher temperatures and longer residence times lead to a growth of the diffusion layer (e.g. during storage and soldering).

4.

The following can be derived from the items 1 to 3: Chemically deposited layers are plane but very limited in thickness. This results in a high danger of loss of solderability as the diffusion layer may penetrate the entire thickness of the coating under certain circumstances in which case the plane surface “ennobled” for soldering is not solderable any longer. On the other hand, a physically deposited soldering surface has a much higher thickness which under normal circumstances is several times thicker than even a seriously grown diffusion layer. However, it is to be considered that this coating has the disadvantage of a lacking planarity.

5.

The customer must specify the requirements which will be verified by BYSCO.

Leaded surface coating
There are certain application areas where the use of leaded solders is currently still legal. The following coating will be supplied only upon explicit written order.

HAL leaded
In terms of topography, layer thickness, shelf life and solderability this HAL layer is very comparable to the lead-free HAL layer. This soldering surface coating is not RoHS compliant!

Please contact at sale@chinapcba.com if you need urgently quote. We will reply you within 2hours after received your email.