Super High Throwing Power Nickel Plating
Ordinary electrolytic acid nickel plating bath have many advantages and are easy to operate because they can be used without additives or with relatively easy to control additives. However, one clear disadvantage is their lack of throwing power, or the ability to deposit nickel in a variety of locations without elaborate anode/cathode arrangements.
Research into superior nickel with exceptional throwing power has been underway for years in laboratories throughout the world. Uyemura has been able to resolve this throwing power issue with the Thru-Nic process, a solution proven to have an enormous increase in throwing power.
We have 11 different solutions available to meet the needs of various users, such as barrel platers, lead frames, and PCBs. Throwing power and covering power (as shown in Table 1) has been improved to such an extent that Thru-Nic can easily be distinguished from traditional Watts or sulfamate acid-nickel baths.
The Family Thru-Nic Solutions
The Thru-Nic family can be broken down into different groups: A, C, T, and G types. The code letter “L” and “H” are used to represent whether they are applicable for low or high current density. “M” represents the make-up solution.
Both Types A and C are low halogen solutions. C contains no chloride ions. The G type contains a medium concentration of halide while the T type contains a high concentration of halides. The deposit appearance from the A and C types are an even, non-bright white. The C type has bigger deposit crystals and appears somewhat whiter than the A type. For a white-gray , non-bright appearance, use the G or T type baths. To achieve a half bright or fully bright deposit, the Thru-Nic S-500 additive may be used.
Measured by a Haring cell at a 5:1 distance ratio, calculated using the Field techniques, our results indicate that the best performers were: T-M, G-M, A-M, and C-M, with respectively, 50, 40, 35, and 30%.
T% = (P-M)X100
T = Throwing Power
M = Plating weight ratio
P = Distance Ratio (5)
Low current density Thru-Nic baths have exceptional throwing power. Our results show that for low current density applications, the best performers were: TL-M, GL-M, AL-M, and CL-M with respectively 90, 80, 70, and 50%. Using Thru-Nic TL-M, barrel and rack plating with a cathode current density of 5 ASF can achieve a throwing power nearly as good as electroless nickel.
High current density Thru-Nic throwing power is 25% for AH-M and 20% for CH-M.
100 gram weight was measured to 15 seconds on a Vickers hardness meter. Hardness of Thru-Nic T and A were slightly higher than the Watts type process and that of C and G were slightly lower.
Thru-Nic internal stress was found to be the same as or slightly lower than Watts type baths. Specifically, the T and G types have relatively higher internal stress while the A and C types were lower.
Deposit properties of the Thru-Nic process are similar to the Watts-type processes with the exception of throwing power, where Thru-Nic is clearly superior.
Current efficiency was calculated from the weight of nickel deposition compared to the amount of current consumed. The current efficiency was found to be 3-8% lower than that of the Watts-type bath, due to the prevention of nickel deposition onto the high current density areas and easier deposition in low current density areas. Even though the current efficiency is lower than the Watts-type bath, the nickel plating ratio for low current density parts is 2 to 5 times faster.
Thru-Nic solutions are used for plating leadframes, hoops, IC packages, capacitors, and connectors as well as PCBs. Thru-Nic is also suitable for barrel plating.
Operation and Control
The make-up solution is ready to use, no solutions or additives need to be added. The make-up solution just needs to be added to the clean tank and heated. Replenishment is normally performed with two solutions, one for the nickel metal and the other for the conducting salt.
There are requirements for nickel plating that ordinary nickel plating baths can’t achieve or have difficulty achieving. Thru-Nic can normally help achieve these requirements easily. In many applications, the plating time will be decreased by one half to one third and better throwing power will be seen.
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