silvering for photoresist mastering

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SRSanford10
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Location: Long Beach, California

silvering for photoresist mastering

Post: # 6439Unread post SRSanford10
Sun Oct 04, 2009 2:47 pm

I have been following the forum for some time, but this is my first post. I am considering attempting laser based recording . The recording medium would be a flat smooth substrate coated with a thin film of positive photoresist. After the test recordings, the discs would, hopefully, be silvered using the same process as with analog phono records.
My question relates to the silvering process. I have a technical article by P. Legierse of Philips in Holland from 1987. "Mastering technology and electroforming for optical disc systems". Mr. Legierse shows by electron microscope images that the conventional silvering process for phono records of that time was quite "grainy" when used for a resist covered glass master. The signals desired for the Laserdisc of about 1 to 2 microns length were being perturbed by the silver grains which were about 0.1 micron diameter, with clumps as large as 0.8 microns. This led to a poor signal to noise ratio. Philips was forced to use an expensive process of vacuum evaporation of silver. I'm wondering if there has been progress in the electroless silvering operation since that time which would lead to smaller sized grains and a more even coverage on a variety of surfaces including thin films of photoresist?
SRSanford10

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fusionkid
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Electroless Silvering

Post: # 6441Unread post fusionkid
Sun Oct 04, 2009 5:05 pm

Hi SRSanford10
I have experience in commercial PCB manufacture, electroless silver plating is now commonplace, and it is one of the more reliable plating processes too. The silver bonds really well, and is less sensetive to contaminants etc, so a better bet for doing at home, can't remember the name of chemical co. at the moment, but all the info should be out there for the PCB application, may be a good start point.

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SRSanford10
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Post: # 6442Unread post SRSanford10
Sun Oct 04, 2009 5:49 pm

Thank you to Fusionkid for that information. I will try to follow up to locate sources of chemicals for PCB work and see if this might work for my application.
SRSanford10

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mossboss
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Silvering

Post: # 6446Unread post mossboss
Mon Oct 05, 2009 10:05 am

Hey
I am not so sure that this is right I mean the size of the silver being around the .8-1 micron range I do not think that the size of single silver molecules are anywhere this size
I the silvering process of a lacquer your aim is to get a mono molecular or a single layer of silver on the face so as to make it conductive This of course is impossible in practice in particular when compressed air and a spray gun is used
From experience I can vouch that from different suppliers you will get a variation of silver nitrate from a purity point variation being from extremely good to useless for the purpose Having said that if you are aiming at an AR grade of the product the amount of silver content should be your guide line any less than 67% of silver content should be avoided as the mpurities as well as the nitric acid used in its manufacture will make up the balance finding its way to the lacquer keeping these molecules apart
The silver used in PCB manufacture is not good enough for silvering of audio lacquers so I doubt that it will serve your purpose
The best material to use in an electroless application of silver is the photographic grade used for high res film production I am not sure where you are located but it is certainly available in the USA If you can get it it is an ok product as the acid has been removed from it getting to an even higher level of silver content
Your other issue is the water used It should be Double De ionised or the best distilled you can get your hands on
If you search for the Alpha Toolex plating system for cd manufacture the steps as well as the materials required are outlined there
A visit to a friendly CD manufacturing (replication not duplication) plant will not do you any harm either
Another strong suggestion I can make is to study the number of patents relating to CD reproduction as well as silver nitrite, there are quite a lot of them Some simple some quite complex and some outright impossible to understand Above my head anyway you may get some milleage out of them
Cheers

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fusionkid
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More Thoughts

Post: # 6453Unread post fusionkid
Mon Oct 05, 2009 4:06 pm

The chemicals I used were from US they supplied photographic stuff too.
I wasn't involved in the silver process much, i worked electroless copper now the catalyst for copper (can't remember name at mo') is V V expensive i used 4.5 litre bottle = £15000 which made about 300 litres of solution. Worth checking what else you need eg Formaldehyde and whether you need license (or mortgage) to buy/ store. you do in the UK

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SRSanford10
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Location: Long Beach, California

Post: # 6470Unread post SRSanford10
Wed Oct 07, 2009 3:27 pm

I was away from the computer for a couple of days, but I wanted to thank mossboss and fusionkid for their useful information. I looked again at the 10,000 times magnitication photos in the P. Legierse article and need to explain that the fact of some "globs" of the silver being about 0.8 microns(randomly scattered across the disc ) was clearly an undesired outcome of this unsuccessful silvering process for the silvering of the Laserdisc masters. The second electron microscope photo at the same 10,000 times magnification showed the result of a vacuum evaporation process for the silvering , which worked well. The grains of silver are very even and appear to be about 0.01 to 0.02 micron in size.
The information from mossboss about the percentage of silver in the silver nitrate was helpful as was the information on water purity. I will spend some time researching the areas mentioned and possibly visit a CD replication plant.
fusionkid brings up a useful point about obtaining useable quantities of these chemicals. Years ago when I was in high school this was not too difficult to do, but the world has changed since then.
SRSanford10

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mossboss
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Silvering and all that

Post: # 6485Unread post mossboss
Fri Oct 09, 2009 7:53 am

Ok Here we go
As I said air spraying the silver is a bit of a hit and miss process The fact that we have been doing it for over 50 odd years and have a few million of lacquers done with the process we have learned how to avoid the pitfalls therefore we get a result
Vacuum metalising will allways give you a much more even and controlable coating
However your base cannot have anything in it that will "bleed" out under a high vacuum and this is the reason that when lacquers come into play vacuum metalising as well as sputtering gave way to chemical silvering
The lacquers release the volatiles and ruin the coat of silver
It may be best for you to seek someone who makes microphones in which case the membrane is vacuum metalised Pelluso comes to mind I am sure there are others
However there is a method which measures the thickness of the silver which I will be happy to post up if you are going to persue it
There is no way to avoid "globules" as you have pointed out but there is a caveat in this It is mainly the result of "horns" in the cut lacquer which is a far less of an issue when you "burn" the master for a cd as you are only looking for highs and lows Given correct solutions Dust control as well as precise and defined procedure and steps you should get excellent results with chemical silvering
Since I have been involved in all of the above over the years I will not persuade you one way or another it is a case of $$$$ and if you want to spend a bunch of this comodity for vacuum equipment as against $ for some spray guns and a simple booth to spray in I am not going to tell you which is best Nevertheless silvering is still used today with a high level of success in cd production worldwide Since this is a vinyl related forum I am not even sure why I am talking about CD but at the end of the day the steps are nearly the same in so far as production methods are concerned and I really hope you can have a go and make real good music even on cd Ha Ha
Cheers

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SRSanford10
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Post: # 6496Unread post SRSanford10
Fri Oct 09, 2009 9:03 pm

Thanks again to mossboss for sharing his experience in the silvering process. I am slowly getting together pieces for the experiments. The biggest plus lately has been that blue/violet lasers can now be found in the U.S. for $25 or so. This wavelength is necessary in order to expose photoresist. I know that this is way off to the side of what most people in the forum are interested in. Now I have to set up some rudimentary optics assembly and electronics test generators without offending my employer or my wife!
SRSanford10

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mossboss
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Location: Australia.

Silvering and Wifes

Post: # 6498Unread post mossboss
Sat Oct 10, 2009 6:35 am

SRSanford10 wrote: Now I have to set up some rudimentary optics assembly and electronics test generators without offending my employer or my wife!
Hey Don't upset the wife It is not a good idea Your boss you can replace the wife as well but the first will not cost you the second will be something you don't want in your life :wink:
Good luck with it all, you are welcome to ask anything related to the subject You are certainly different from a lot of others They get on ask a whole heap of questions get some or all the answers and you never see another post from them Arghhhh
Any way If we can help you with anything you ask, I am sure you will get a response from someone here
Cheers

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mossboss
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Silvering and Wives

Post: # 6508Unread post mossboss
Sun Oct 11, 2009 6:26 pm

Hey SR
Here is a link for you! http://www.10000cows.com/deposition_system.htm The guy says it is not for the "Faint Hearted"
I agree
Neveretheless the photos are very telling the results nothing short of fantastic
I had to try and remember the site as it is a while since i come across it so it took a while for the memory bank to "fire up"
Cheers

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SRSanford10
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Joined: Fri Aug 14, 2009 9:26 pm
Location: Long Beach, California

Post: # 6509Unread post SRSanford10
Sun Oct 11, 2009 9:30 pm

I was just looking again at fusionkid's information on the cost of the catalyst for the copper plating operations. I was trying to do mental arithmetic while fellow workers are concentrating on American football games...So I got about 80 U.S. gal. into about 15000 English pounds might be about 170 English pounds per gal. or perhaps about 280 U.S. dollars per gal. Hopefully, a gallon might keep me going for quite a while.I have to assume that some high purity silver nitrate might be about the same order of expense.
Thanks also to mossboss for the web site with the very interesting pictures of the home brew vacuum chamber plating system. I don't believe that I would be able to do such a thing myself, but perhaps I could make a financial contribution to have someone plate some of my tests. It occurred to me that it would not be necessary at first to plate the full round disc; a section of the disc would give me the technical information I would need to get some control over the recording.
SRSanford10

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mossboss
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Silvering

Post: # 6510Unread post mossboss
Sun Oct 11, 2009 11:00 pm

Hey SR
Silver Nitrate in the form of crystals is around $1 per gram as a rule of thumb
Five grams do about 6 square feet, more or less, including all other chems, say $1.25 per square foot of surface area or about 4-5 cd,s if you are carefull with the loose spray
So save the research on this one
Vacuum apart from the cost of the equipment, material cost is about the same
However with vacuum metalising you have a choice of metals or their salts
Gold silver nickel including the exotic rare stuff is easily done resulting in a far better or almost perfect control of the coating
The average motor car head light reflector is vacuum metalised with pure aluminium, a thicknes of around 50-60 millionths of an inch is applied by calculating the area to be covered with the appropriate weight of the metal placed in the "boat"
Once the coating is done the reflector is than sealed off with the lens cover etc etc etc
Hope this is of some help to you
Cheers

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SRSanford10
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Post: # 6543Unread post SRSanford10
Wed Oct 14, 2009 7:40 pm

Thank you again to mossboss for that very helpful information on the options for silvering and the costs involved. I need to get further along now with obtaining the optics and finding out more information on modulating the laser without destroying it. I hope to be able to repurpose some consumer product mechanical assemblies for the tests.
SRSanford10

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