Issue:
1. Getting some burn, on edges, would like to be able to increase current density.
2. Getting whisker growth on edges, would like to minimize.
3. Stannous sulfide buildup on anodes is quite a bit, we clean then every 24 hours.
4. Pure sulfur is coming out of solution, gets on the bottom of the tank, inside the parts. It
rinses off but unsure is this is an issue, or just normal. I’m guessing it’s a by-product of the
stannous sulfide reaction. We filter the tanks as necessary and remove.
Suggestions:
1. Getting some burn, on edges, would like to be able to increase current density.
- As I research and observed, the mixture between the existing bath and battery acid are
compatible in some area of the material but in edges there are some effects. Since the
battery acid (sulfuric acid) is more concentrated which is 20% than the existing bath, we
need to consider the area when it is process. I research about PEG and it indicated that it
is additive to maintain the concentration and I observed that the solution is very
concentrated that is why there some burn issue on edges. But I will further research
about this problem and improve the process.
2. Getting whisker growth on edges, would like to minimize.
- The mechanism of tin whisker growth has been studied for many years. Although its
mechanism is not completely understood, it is mainly theorized that such growth is caused
by compressive mechanical stress gradients, such as residual stresses caused by
electroplating; stresses caused by the diffusion of different metals, thermally induced
stresses or mechanically induced stresses.
-Mechanically induced stresses are externally applied compressive stresses caused by
bending or stretching the surface after plating.
-Thermally induced stresses are developed because of the mismatches in Coefficient of
Thermal Expansion (CTE) between the plating material and substrate.
Mitigation/Reduction Strategy
-Use of an underlayer between the base material and the Sn layer.
Use of an underlayer, also known as barrier layer, between the base material and
the tin layer is another way to try to control whisker growth. Nickel is the underlayer
most reported on as used between Sn and Cu, with some claims of total prevention
of whisker growth while others report only damping of whisker growth.
- As I research, I have list of studies gathered about this mitigation strategy that already
experimented which follows according to this:
1. Role of Underlayers on Whisker Growth
2. Role of Tin-Oxides on Whisker Growth
3. Role of Grain Structure on Whisker Growth
4. Whiskering Properties of Structures with Underlayers in Humid Environment
5. The Effect of the Grain Structure of Tin on the Whisker Growth
6. Whiskering Properties of Tin-Copper Alloys in Various Humidity Condition
Also, I have another four mitigation strategy which can help to reduce the whisker
growth on edges. As I research, there are whisker growth model that being used to
determine the size of it and why is there are formation of whiskers. As of now, I
study that different kinds of model.
I have research about the CuSn6 which indicate the base material that being used in
the process. CuSn6 is a solid solution strengthened copper alloy (bronze) with 6%
tin. The alloy has high strength and good springiness at an adequate conductivity
and is well suited for cold forming operations. The alloy is wear-resistant, has very
good corrosion resistance and can be readily soldered.
Also, I found an experimentation about CuSn6 as base material. There are other two
base material used such as CuSn0, 15 and E-Cu58.
3. Stannous sulfide buildup on anodes is quite a bit, we clean then every 24 hours.
- I suggest to use purified water to clean so that there’s no contamination going.
Sometimes, contamination can affect problems in the product. And also, I research
about a cleaning system and chemical used on anodes. But I need to verify first and
gather information so that there’s no complication.
4. Pure sulfur is coming out of solution, gets on the bottom of the tank, inside the parts. It
rinses off but unsure is this is an issue, or just normal. I’m guessing it’s a by-product of the
stannous sulfide reaction. We filter the tanks as necessary and remove.
As I research about this by-product and I saw this reaction in article :
-
The by-product of the stannous sulfide reaction is known “Stannous oxide”.
Tin(II) Oxide (Stannous Oxide) is a highly insoluble thermally stable Tin source
suitable for glass, optic and ceramic applications. Tin oxide is a colorless inorganic
compound of tin and oxygen and has two forms, a stable blue-black form and a
metastable red form.
These are the samples of stannous oxide powder and what color of the by-product
you got?
“It rinses off but unsure is this is an issue, or just normal” – as indicated,
it is important to rinse off using purified water or hot water. There are some reaction and
contamination when it is not properly rinse.
