Letter 5007

Stripping titanium nitride PVD coatings

(2000)

Seeking a source of a stripper for PVD coating (titanium nitride). A variety of substrates is involved. Thanks

Ken Lemke Canadian Finishing Systems Ltd Burlington, Ontario

Concentrated acids, especially hydrofluoric, will dissolve PVD TiN. It is even more difficult remove CVD TiN due to the more conformal surface. Unless your substrate is glass or ceramic, there is a strong likelihood the substrate will be significantly damaged removing the nitride with this method. Sorry, that is one of the advantages TiN surfaces--the fact that they are so hard to remove!

Dale Woika
- Bellefonte, PA

A combination of alkali and hydrogen peroxide are useful for removing titanium nitride from stainless steel (I would recommend a 5% (w/v) of KOH to which is gradually added approx 30% hydrogen peroxide solution (no more than 20 L to a 100 L KOH solution). The H₂O₂ is added slowly so as to control the temperature of the etch solution. If the temperature of the solution exceeds 30 deg C oxygen is evolved rapidly and the solution will foam up uncontrollably. Ammonia solution can be substituted for alkali (KOH/NaOH) for etching titanium nitride from aluminium.

Brendan Timmins
- Limerick, Ireland

Also seeking a solution for removing PVD TiN. Without damage to the underlying ceramic (AlN) substrate.

Jason
- Daytona Beach, Florida, USA

I run a PVD job shop in India.

Most common method for stripping Titanium Nitride is to use 30% or 50% hydrogen peroxide (H₂O₂) - this works with stainless steel and HSS substrates. But this is slow; will take up to 8 hours. Use a container big enough to allow for foaming and also keep it ventilated; keeping it in sunlight speeds it up.

Catalysts such as NaOH and EDTA speed up the process, but needs more control.

For stainless steel 304 grade, nitric acid + HF works well - over in minutes - but you have to be careful with concentrations (we use 3:1 ratio) to avoid etching of substrate; with 410 grade; we tried, there was heavy etching. Right now we are staying with H₂O₂

Caution: do not use with tungsten carbide.

Kuppu Swamy
- Chennai, India

I work for a PVD company that deposits hard coatings such as TiN or TiAlN on steel substrates. We developed a stripping process which is a mixture of NaOH and hydrogen peroxide (H2O2).
First, I am trying to figure out what is the waste produce by the stripping reaction? Second, when I transferred the process to production I have had some difficulty in controlling the reaction. In our lab, even at high temperature (~70degC), the foaming doesn't get out of control but in production we have had a few overflows due to excessive foaming. One difference that was identified is the use of a steel tank in production as opposed glass beakers in the lab. Any thoughts?

Steve Guetre
engineer - Montreal, Canada

I am a bit surprised that you did not have any problem in the lab at 70C.
The breakdown from heat of H2O2 appears to be logarithmic. It becomes self destructing extremely rapidly at some temperature. I have seen it become nearly explosive. I bear the burn scars from it.
In production you may have more material to strip per unit of solution . Heat is a product of the breakdown.
If units are comparable, then I will guess that in production you are generating more heat than the tank can get rid of whereas in the lab the heat transferred to the atmosphere faster for some reason.
Possible solutions would be to strip less material at one time paying close attention to the initial temperature, or adding a cooling coil that would kick in at a given temp to control the temp rise.

James Watts
- FL

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