Sio2 Layer Peals off after Boiling

[sujeet]

Another Day,

I have a peculiar problem with my AR Coating.We boil the test lens immediately after the Coating. The boiling is done on Saltwater. After boiling if we scratch test the lens, the last Sio2 Layer comes OFF, 99% times from the front surface of the Lens. Seldom its the rare side.The process wise both the sides are done in the same fashion. The lenses are dip hard coated. We use Al2o3 between the long Tio2 or Zr layer and the sio2.
Anyone has suggestions??

[Falstaff]

Hello,
We have seen something like this before after salt water boil tests. i.e. what appears to be a partial loss of the last SiO2 layer, usually around the edges of lenses.
Presumably your lenses pass the scratch test if they are not boiled, so it is not just an ion source problem, or something similar.
I am not sure we have any answers but it would be interesting to know a little more about your process.
Best regards, Falstaff.

[sujeet]

The process is like this :
Ion Gun Etching for 5 Min @ 2.5A emmision current
SIo
Tio2 or Zr ( Tio2 with 12 Sccm of O2)
Sio2
Tio2 or Zr ( Tio2 with 12 Sccm of O2 )
Al203
Sio2
Hydrophobic

After Boiling all the layers remain intact, except when you scratch test the boiled lenses with steel wool. The Last Sio2 could be Scratched off. Its happening randomly. We have 6 coaters. It happens on all the machine, like today on one machine, tomorrow may be nothing, other day on other machine. Its pretty random. On top of it, its mostly on the front surface of the lens. Very seldom on the back side.
By the way, we do the rare side first, then coat the front side.

The coating does not peel Off or scratch off from the side. Its all over the place.

Regards

[Falstaff]

Your process seems very similar to ours, although we do not use TiO2 any more. I have only really attacked the cross hatched areas after a boil test with steel wool, but it usually does not cause any damage. I will try what you do after my next boil test.
I understand that the Al2O3 layer is an adhesion layer, and seals the underlying stack. I assume you have come to the conclusion that the final SiO2 layer is missing from a spectroscopic analysis of the remains of the coating.
We have had many theories as to what may be happening in our case, but none have so far been wholly successful. Some of our affected lenses were sent away for analysis, and it was suggested that the underlying hardcoat lacquer was to blame, though it is clear from spectroscopic scans that the lacquer is still intact.

Regards,

Falstaff

[sujeet]

We do Salt water test. by dipping 2 min. in hot and 1 min in cold for 8 times. Did you try boiling after the run and scratch with still wool , yet ?

[Falstaff]

Just completed a test with lenses from 4 of our 5 AR coaters. There were some rough cross hatch lines on the cx sides (yes, it always seems to be this side), some redness near the edges (a common occurrence for us), but steel wool and scotch-brite did not remove any of the coating.

Regards,

Falstaff

[sujeet]

Thanks. Did you coated the Backside first, or front.

[Falstaff]

We usually coat the backside first, then the front. Are your pump down times normal? Do you think that there might be very small amounts of moisture in the chambers? This affects adhesion even though start pressures are still reached.

We were told that we shouldn't really test a coating till it is 24 hours old, but this is not always practical. Your boil test is also more severe than ours, which is just 6 cycles of 1 min boils and short room temperature D.I. water dips.