Lead-Free Solder and Stainless Steel

Hari Is this what you are asking?

While heating whether the stainless steel/ material composition of Stainless Steel tank will effect the quality/composition of solder? which eventually may effect the solderablitiy of solder.

Hi Rakesh,

Yes! you catch my point..

Hari

It depends on how quickly you consume one bath qty of solder, There is always a minuscule amount of diffusion from solid to liquid, But I don't think its going matter if you consume one bath in few days specially if its a SS tank.

However quartz and graphite crucibles are used in some cases to solve this problem.

I observed this in a pressure die casting unit where body of large thermocouple was consumed in aluminum, and thats of electrical grade.

One more thing goes in your favor is the low melting temp of solder, Higher the temp more is diffusion.

Hello, PLEASE READ THIS!!!!

You have a very dangerous situation and you need to consult NOW with your equipment supplier.

The problem is not the amount of stainless steel that will contaminate your solder.

The real problem is "Where is that stainless steel coming from?"

Lead free solders are notorious for disolving stainless steel tanks and "eating" holes through them (and consequently dumping molten solder onto the shop floor at an alarming rate.)

There are multiple examples of tank failure (especially close to the pump where the localised pressure increases the erosion process).

In my opinion, you need to replace the tank.

Agreed! It's not a matter of if it will happen, it's just a matter of time and it will happen. Change the tank material before it happens.

I think Its not that alarming as you tend to.

It will take years before it happen, Of-course SS has to be thick enough.and whats for the preventive maintenance?

Rakesh,

I respectfuly ask "Have you've seen a wavesoldering tank in use?"

My experience with five machines is that the solder is not used as a batch from the tank, but rather the tank is maintained at full condition and there are submerged in the molten solder portions of pumps, baffles and other bits of hardware. There is no opportunity to see the inside surface of the tank once it is in normal use.

The submerged pump creates a high pressure flow through a channel inside the vat that elevates a portion of the solder till if flows over a wier back into the vat. (Hence the term "wavesoldering")

I have heard of tank failure within 150 days of starting operation. (Not just the pictures, but the actual tank.)

I have seen an eroded pump impeller that caused process adjustments to pump speed as it steadily disolved into the solder vat until it was unable to pump the solder. (Yes I saw this impeller also, not just pictures.)

Imagine if you will 600Kg of molten solder "leaking" through the borrom of the tank in less than 10 minutes onto the vinyl floor in a cleanroom environment. Smoke, fumes, confusion, DANGER.

As I initially suggested, the OP needs to contact his equipment supplier/manufacturer and get their feedback on this issue. It's not something to guess about.

Hello,

Thanks for all your advise!!!

I did contacted the Quality/Production guy of solder bar manufacturer[cookson], they replied" that the nickel content present in the SS might have a light influence over the solder ability" but it's not too that much extent...

Albeit,they prefered "Cast Iron" coated tank!!! Comment on this !

For your Information: Still now we are using CI coated tank[Total tanks 30], but the story why we proposed to go for SS tank is depicted below:

" CI coated tank seems to get corroded as quickly & it reach his life time within a couple of months. But in the same hand, SS coating evidenced to withstand for a longer life ( double or triple the life period of "CI").

Added to that, i observe the presence of chromium [18%] in the material composition of SS. I believe, you all aware that "Hexavalent Chromium" is a restricted substance under ROHS list.. Is this "Cr+6" will present in chromium..

Note: Our cycle time of solder tank cleaning is 3 months once!

Need your valuable suggestions to fix the thing!!!

Hari

As I've said twice, contact the equipment supplier about the options for tanks (and impellers and baffles and channels) that are suitable for the solder composition that you are using.

Your solder supplier has confirmed what I though they would "That solderability will not be affected." [Since there will only be relatively small amounts disolved (and thus contaminating the solder) at any given time]

The issue at hand is the life of the tank. There are other metals provided by suppliers that are suited to the new solders, but you need to match them properly.

We do "deep clean" every week, but never empty the vat. (Up to 12 years in service)

The basic principal that is understood is that "If your solder can wet to the tank material, then the solder can dissolve theh tank material."

As far as ROHS and the Chromium content, I'd be looking for clarification from your customers. The chromium is not an "intentional" part of the manufacturing process (It seems) and so is not in your "ingredients" list, but you know that it will be present and thus it should be accounted for if you use the SS tanks.

You should be brazing. See the American Welding Association web page for guidance on how to go about this. Solder is not going to maintain its integrity at those temperatures.

Boy, I must be confused. Brazing what? As I understood the question, this is a solder melting pot operating at a high temp of 782F (400C). Where did I go wrong?

If my misunderstanding of the issue detracted from the quality of the responses, I apologize.

The temperature of up to 400°C is not high enough to cause any reaction with the stainless steel which would effect the solderablitiy. I expect you are using this in regard to electronic Assembly's so you would be using neutral fluxes which would not attack the SSteel.

Note for all.

The lead free solders usually have copper and/or silver in them which can alloy with the SS material and steadily dissolve the tank from the inside out. The concern is not the flux, but the action of the constituents of the solder itself.

SS tanks are quite OK for typical lead based solder and were the norm for almost every machine made in "the good old days". The change to lead free solder is exactly why these questions are being asked now relating to tank durability.

Some of the early operators had some very nasty surprises when tanks failed.