Vacuum Web Coating

AIMCAL Converting School 2010 Schedule

February 16 - 18Nip Roller Workshop
Rochester, NY

February 25 - 26Drives in Web Handling and Converting
Schiller Park (Chicago), IL

March 16 - 17Web Handling and Converting
Atlanta, GA

March 18 - 19Winding: Machines, Mechanics and Measurements
Atlanta, GA

April 13 - 14Solution Preparation and Mixing
Philadelphia, PA

April 13 - 14Web Handling and Converting
Brussels, Belgium

April 15 - 16Web Coating and Drying
Philadelphia, PA

April 15 - 16Winding: Machines, Mechanics and Measurements
Brussels, Belgium

April 20 - 22Web Wrinkling and Spreading Workshop
Rochester, NY

May 4 - 5Solution Preparation and Mixing (Europe)
Brussels, Belgium

May 6 - 7Web Coating and Drying (Europe)
Brussels, Belgium

June 8 - 9Optimizing Extrusion-Based Lamination and Coating Technology
Rochester, NY

June 15 - 17Center Winding Workshop
Rochester, NY

August 17 - 19Roller Performance Workshop
Rochester, NY

October 5 - 6Web Handling and Converting
Philadelphia, PA

October 5 - 6Web Coating and Drying (Europe)
Brussels, Belgium

October 7 - 8Winding: Machines, Mechanics and Measurements
Philadelphia, PA

October 7 - 8Drives in Web Handling and Converting (Europe)
Brussels, Belgium

November 9 - 10Solution Preparation and Mixing
Cleveland, OH

November 11 - 12Web Coating and Drying
Cleveland, OH

Visit www.AIMCAL.org or www.ConvertingSchool.com for more information.

Cooling water quality - process effects.

Below is an article posted on the PVD Forum by Eric Kurman.  It primarily deals with the problem of conductivity of water for use in magnetron sputtering sources.

 

However many plasma cleaning units are based on the same magnetically enhanced design as the sputtering sources and so the same factors apply.  

 

It is also worth noting that over time ‘dirty’ water can fur up pipes, fittings and deposition drums which can adversely affect the cooling performance. Often this furring process will take many months or even years and so the changing performance may not be noticed easily. Also it may be assumed that a slowly degrading performance is just the machine aging.  So periodically during major maintenance it is worth checking that pipes are remaining clean and that the flow is not being restricted.  

 

 

 

‘Dirty’ water cooling of magnetron sputtering sources.

 

There is a little more to the story on water.

First of all, "dirty" is really a misleading term, the water does not have dirt in it, rather it has dissolved ions leading to an increase in conductivity. This is common in Process Cooling Water loops or so-called "house" water and can come from two sources.

a) Intentionally, from treatments placed in the water to inhibit corrosion.
b) From corrosion due to wetted surfaces in contact with the water.

Most engineered PCW systems exercise very close control on which surfaces are allowed to be "wetted" in contact with cooling water. However, most thin film systems in my experience have a profusion of wetted materials including various polymers, brass of different types, copper, zinc, tin, chromium, stainless steels of different types, and occasionally target materials from directly cooled targets.

Another problem is that grounding is often sloppy in thin film systems and the machine frame is used as a common for power line ground and return current from a deposition component like a sputter cathode or electron beam hearth.

As others have pointed out, the conductivity of the water needs to be measured. However it might not be as simple as "replacing the dirty water". The DI water can corrode certain materials particularly copper and brasses. Once this happens the water is no longer "DI", and once the conductivity of the water increases, there is the potential for electrochemical corrosion due to dissimilar materials being wetted and voltage applied to components in the loop.

Even in the case of the heat exchanger technique (we used to call them "mini-loops" ) mentioned in previous message, often the water does not stay "DI" for very long. I have looked into the reservoirs of many a mini-loop to see stuff that looks like it belongs in a mud puddle.

The only way to continuously maintain low conductivity is to include a polishing bed in the recirculating loop....kind of expensive but, if you are running production, often worth it.

Knowing the conductivity of the water one can estimate the power drop due to conduction through the water circuit. Electrical power flows from the high voltage component to the nearest ground or return component. You will need to know the internal cross sectional area of the tube or pipe and its length.

Let's assume you are cooling with typical drinking water that has a conductivity of 0.01 S m^-1 and that you have a magnetron cathode running at 500V, connected to ground with two 1/2" (12.7 mm) plastic tubes that are each 1 m in length (two tubes, inlet and outlet, 1 meter long each). Our tube has a wall thickness of 1/16" and an internal diameter of 3/8", thus its cross sectional area is 0.71 cm^2. The series resistance of this water-filled tube is resistivity times length divided by area, namely (10000 Ohm cm)*(100 cm)/(0.71 cm^2) = 1.41 megOhms (1.41E6 Ohm).

The two tubes are in parallel so the total resistance is 700 kOhm.

Note that we had to convert from conductivity, measured in Siemens (facilities and water people always deal in conductivity) to its reciprocal, resistivity, and to also convert from meters to centimeters. Thus 0.01 S m^-1 = 10000 ohm cm.

Your sputter cathode will conduct 500V / 700E3 Ohm = 712 uA to ground. Total power dissipation through the water is about 356 mW. This might be a lot, if you are running a small R&D cathode at a few Watts, or it might be negligible, if you have a bigger system running at 30, 50, 90, etc., kW.

Note that power loss through the water depends only on the voltage drop and will be the same for a small system as a large system for the same water conductivity and tube sizes.

If we repeat the same calculation using seawater (4.8 S m^-1) as the coolant, resistance is 20 kOhm per tube, 10 kOhm total, power drop would be about 24 W for a load at 500V. Water is just not very conductive, even seawater!

So you have two main choices: change the water, or use a longer tube. The latter is a surprisingly effective way to go. It is not that big a deal to coil up 50 or 100 feet of poly-flow tube, tie-wrap it in place, and fix the problem.

If you are running an EB setup at 10 kV or 20 kV or higher, or maybe an X-ray tube at 50 kV to 100 kV, you have a bigger problem. Low conductivity coolant and a long path length is a requirement here. Oil coolants can be used but they have lower heat capacity than water and a big headache as well.

So....do the measurements. ...do the math....analyze and determine a solution.

 

"Eric Kurman" <ekurman@yahoo.com>

AIMCAL FREE WEBINAR SCHEDULE

January 12, 2010, 11:00 AM -12:00 PM Eastern
Coating Solution Preparation Technology
Ken McCarthy, Clean Room Coating Solutions
Edward Cohen, Ed Cohen Consulting

 

January 19, 2010, 1:00 PM - 2:00 PM Eastern
Your Legal Responsibility for Legacy Machinery

Mike DeRosier, AH&T Insurance

 

February 10, 2010, 11:00 AM - 12:00 PM Eastern
Contract Coating For Development or Manufacturing

Larry Gogolin
Edward Cohen, Ed Cohen Consulting

February 16, 2010, 11:00 AM - 12:00 PM Eastern
Resistance Heated Evaporation of Aluminum - The Basics
Dr. Charles Bishop

 

February 18, 2010, 11:00 AM - 12:00 PM Eastern
Reducing the Carbon Footprint: Making Sustainable Flexible Packaging
Giancarlo Caimmi, Nancy Smith, Rick Gloeckler, Rich Castillo and Stewart Richards

 

March 2, 2010, 2:00 PM - 3:00 PM Eastern
On-line Coating Weight Measurement
Hector Marchand

 

March 16, 2010, 11:00 AM - 12:00 PM Eastern
Winding Webs in Vacuum - including Heat Load
Dr. Charles Bishop

 

April 14, 2010, 11:00 AM - 12:00 PM Eastern
Vacuum Deposit Barrier Coatings
Dr. Charles Bishop

 

May 12, 2010, 11:00 AM - 12:00 PM Eastern
Troubleshooting - Process/Adhesion/Vacuum
Dr. Charles Bishop

 

June 16, 2010, 11:00 AM - 12:00 PM Eastern
Reactive Deposition by Magnetron Sputtering - The Basic Process and System Design Considerations

Dr. Charles Bishop

 

To register for any of these webinars go to http://www.convertingschool.com

and go to the box with the AIMCAL logo and pick the webinar you wish to register for and click on the link. 

 

 

 

 

 

Adhesion – the No. 1 problem

Looking back over the questions asked over the years it appears that adhesion is the problem that causes the most difficulty.  This is either directly as poor adhesion when tested by the simple tape test or as evidenced by problems experienced downstream by customers using the coated films.

 

It does not really matter where the problems are experienced the process for trying to sort out the problem saves the same.  Firstly compare the process from when it worked well to now it does not work and look for the differences. This needs a holistic view of the process starting with the incoming film and things like the weather. In some countries the weather can change hugely both in temperature and humidity from season to season. Treatments such as corona can be affected by changes in humidity and so a change in season may require a re-optimisation of the corona treatment process.  If the film supplier has changed the polymer may contain different additives and the surface chemistry may be different and hence any pre-treatments may no longer be optimised.  Within the vacuum deposition process there can be differences between when the system is freshly cleaned and when the system is dirty and is due to be cleaned.  If the season has changed the cooling water may be at a different ambient temperature and so the cooling of various system parts will be different and the process can differ.   If the pump down performance has changed or the base pressure is different (higher) this can be indicative of a dirty system or a system leak.

 

This comparison is very important as it helps to identify the true source of the problem. Without doing this comparison there is a danger of trying to modify the vacuum deposition process to improve the adhesion when the problem is elsewhere and continues to exist. However this much wider range of possible sources of the adhesion problem means that it is essential to me methodical in comparing all aspects of the process from start to finish.