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topic 56395

Does tin plating need undercoating with copper/nickel?


December 22, 2010

Q. Should TIN plating to done on MS with copper/Nickel under coat to avoid corrosion and oxidation?

ROHIT MATHUR
product designer - INDIA


December 23, 2010

? Hi, Rohit. Please tell us what you are plating and why. This must be described before anyone can tell you what plating processes are best.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey

December 23, 2010

A. Be careful of your nomenclature. TiN is titanium nitride and is applied by one or more of the physical vaporization deposition (PVD) while tin is the metal tin and is also known as stannous or stannic.

James Watts
- Navarre, Florida



Sn plating on MS with Ni and Cu undercoat for soldering and corrosion resistance

August 6, 2018

Q. My situation: I have a part of MS material which needs to pass Salt spray test as per standard ASTM B117 [link by ed. to spec at TechStreet] for 48 hours. The requirement with the part is that it should be solderable after plating. For that I am doing Sn plating over it. But why is the Ni and Cu undercoat required over MS for the same? Can't it be either Ni or Cu rather than both?

Generally we do Sn plating of 4-5 microns with Cu undercoat of 4-5 microns. But we don't get consistent result of 48 hours SST life.

Is there any issue of skinning effect if I go with the plating described above?

RANJIT NAIR
R&D ENGINEER - UDAIPUR, RAJASTHAN, INDIA


August 2018

A. Hi Ranjit. I don't know what you mean by 'skinning effect' … hopefully another reader will.

Copper offers no significant salt spray resistance, so you are asking 4 microns of tin plating to provide 48 hours of salt spray and that is questionable. But thread 31034 will give you good insights into tin plating vs. salt spray hours.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


August 10, 2018

Q. Thank you for your response. What I conclude from the suggested thread are:
1. Sn alone on MS can't protect against corrosion.
2. Cu strike inter layer before Sn plating improves corrosion resistance.
3. Follow ISO 2093 [link by ed. to spec at TechStreet] standard for plating on MS with Sn plating as per the condition part will be subjected to face.
4. Organic sealer/Lacquer helps in corrosion resistance up to three times more but part will not be solder able thereafter.

I would like to get your insight on following two more points:
1. Why Cu undercoat is required before Sn plating on MS? Does it helps in better adhesion of Sn on MS or covers up the porosity of Sn?
2. Is it suggested to do Ni undercoat too in between Cu undercoat and Sn plating? For example: Sn plating 'x' microns with Ni undercoat 'y' microns and Cu undercoat 'z' microns on MS.

RANJIT NAIR [returning]
R&D ENGINEER - UDAIPUR, RAJASTHAN, INDIA


August 2018

A. Hello again, Ranjit. Please understand that I am only the forum curator, trying to help direct you to information available on the site. Although I've acquired some limited book knowledge of a lot of metal finishing subjects, I don't pose as an expert on the subject of tin plating onto steel for the purposes of solderability and corrosion resistance :-)

In the general case, however, I don't think tin necessarily requires any underplate to be solderable and corrosion resistant if it is sufficiently thick and pore-free. I also understand that copper directly under tin plating can cause Cu-Sn intermetallics, which is why you might use nickel in between copper plating and tin plating for parts that will be soldered, and why it would probably not be less than 50 µ.

I think you can better attract experts in your topic if they understand exactly what your topic is :-)
… can you explain what the 'parts' are? Are they chassis parts? Must they carry electricity? What environment are they actually used in? (As you've probably read, designing parts for salt spray survival rather than real-life conditions is not good practice). And I repeat that I don't know what "any issue of skinning effect" means. Best of luck!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


August 31, 2018

Q. Hello Ted,

Thank you for the response and I am extremely sorry for my delayed response. I am the designer of electronic meters and generally deal with MS shield parts which are to be mounted on the PCB for any ESD protection. These PCBs are protected by plastic enclosures from external environment (Though meters can be mounted directly on poles in external environment or in-house in protected environment). The two main requirements with these MS shields are that they must be solder able and must conduct electricity after plating.

For skin effect you can refer below links:
1. https://en.wikipedia.org/wiki/Skin_effect
2. https://circuitglobe.com/skin-effect.html

RANJIT NAIR [returning]
R&D ENGINEER - UDAIPUR, RAJASTHAN, INDIA



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