A blog on the repair, operation and calibration of surface analysis systems and components including electron spectrometers, sputter ion guns and vacuum related hardware. Click on the Index tab below to see a list of all posts. Visit our website at http://www.rbdinstruments.com
An easy way to determine whether or not an ion pump needs to be rebuilt is to perform an endoscopic ion pump inspection. The hard way is to drop the ion pumps.
In the last few years the prices have really come down on USB and android/iPhone endoscopes. If you do a search on EBay for USB endoscope you will see a lot of choices for under $20.00. The one used in this blog post is 7mm in diameter, which is small enough to fit into a 1.33” CF flange hole.
For this example we inspected a PHI 660 scanning auger system equipped with a 220 l/s ion pump. This system has been in use for about 10 years primarily for depth profiling using Argon gas.
Since there is a shield below the TSP filaments the only way into the ion pumps was thru the un-used 1.33 CF flange that is opposite the ion pump high voltage connector.
The color corrected pictures below show that the ion pump elements are pitted, the insulating ceramics are coated and there are some flakes in the bottom of the pump well. The conclusion was that the pump elements have another year or so left on them and so we will plan on replacing them in 12 to 18 months.
RBD Instruments provides all of the parts that you need to rebuild these TNBX ion pump wells. Contact us for more information (www.rbdinstruments dot com) For best results, read this entire post and then look at the pictures at the bottom of the post.
The P-E (Perkin Elmer) TNBX style of Ion Pump well is found on most of the older PHI AES and ESCA systems. It is 12 inches in diameter and houses 8 ion pump elements. There is also a poppet valve that allows you to isolate the ion pump elements, keeping them under vacuum while venting the upper part of the chamber for maintenance. In this blog post we will show you how to access the ion pump elements for replacement or rebuild. The process includes instructions for disassembling and removing the poppet valve assembly, and removing all shielding and the TSP flange.
Important: Read through all procedures before beginning work to ensure you have the necessary equipment, personnel, and tools to complete the process.
Step 1: Remove the upper half of the chamber.
Equipment required: Chain hoist or engine hoist
Turn off all controls and allow the ion gauge filament and the ion pump elements time to cool down.
While the ion pump elements cool, remove all cables from the system.
Prepare a space large enough to for the top half of the chamber. We recommend a piece of cardboard on the floor covered with UHV grade foil.
Vent the chamber completely.
Move the equipment you are going to use to remove the top of half of the system safely so that it’s within range of the chamber. We often use the chain hoist that we have at RBD Instruments. An engine hoist has proven to be a suitable alternative. Additional personnel may be helpful.
Connect the chains from the equipment to the eyelets on the chamber and remove all bolts that hold the two halves together.
Use the equipment to remove the upper half of the chamber. Additional personnel may be helpful to help guide the upper half of the chamber away from the bottom half.
Place the upper half of the chamber in the space you created earlier. It will remain there while you are working on the pumps.
Step 2: Remove the Poppet valve to access the shielding.
Tools required: Two 7/16” wrenches.
You should be able to look down into the chamber and see the poppet valve. You will likely see that the ion gauge that protrudes into the chamber above the poppet valve.
Remove the ion gauge so that you do not damage it while you working inside of the pump well.
Turn the poppet crank so that the poppet valve is all the way up.
Grab hold of the poppet valve and rotate it counter-clockwise to unscrew it from the scissor jack.
Rotate the poppet crank handleall of the way counter-clockwise. This crank handle is located on the side of the ion pump well.
Remove the bolts that mount the poppet crank handle to the flange and rotate the crank handle and the crank housing together, counter-clockwise, until you can remove it from the scissor jack.
Using two 7/16” wrenches, loosen and remove the mounting hardware for the scissor jack.
With the mounting hardware out and the scissor jack free, work the scissor jack out of the ion pump well. This may take some maneuvering, but it will come out.
Step 3: Remove the TSP (Titanium Sublimation Pump) assembly and lower shielding.
Tools required: #1 flat head screw driver, #1 Phillip’s screw driver; 11/32, 3/8, 5/16 and ¼ wrenches.
Remove the TSP cable from the TSP flange. If you’re lucky there is a screw-on connector for removing the TSP cable. The less convenient version has cap-head screws that fasten the wires to the flange feedthru’s. If you need to remove the wires, make sure that you mark the center “common” wire.This is the only wire that has a specific post that it must go to.
With the wires removed you can now safely remove the TSP assembly.
Remove the first piece of shielding. It is the shield that blocks titanium from the upper chamber and the poppet valve. The shielding is removed by loosening the mounting hardware. All shields and mounting hardware should be stored on a clean surface.
Remove the circular cryo shield. This comes apart in sections for easier removal.
You can now reach the high voltage conductor that runs from the high voltage feedthru to each of the ion pump elements.
Step 4: Ion Pump Element removal.
Remove the high voltage conductor. It can either be one solid piece of ribbon or it can come in sections that can be removed one at a time. This conductor can be attached using a variety of different hardware, so be prepared with a variety of screw drivers and wrenches.
Remove all of the ion pump elements once you’ve removed the high voltage conductor.
We recommend that you remove the high voltage feedthru flange for inspection. It can sometimes get coated, and you also may find titanium flakes have worked their way up inside the flange. Once everything is removed and out of the way, you can clean the ion pump well.
Step 5: Cleaning and replacement of ion pump well and associated parts.
Equipment and tools required: Wire brush, shop vacuum
Brush the walls, nooks, and crannies of the ion pump well to remove any build up titanium flakes.
Vacuum out the ion pump well with a shop vacuum. Wrap the end of the hose in foil to prevent smearing the plastic hose with whatever might be on the ion pump well walls. It also prevents transferring whatever might be on the hose onto the walls of the ion pump well.
Use isopropanol and Kim wipes to clean the inside of the ion pump well.
Install the newly rebuilt or brand new ion pumps.
Vacuum out the high voltage feedthru. If it’s obviously coated with titanium you will want to clean off the titanium using a sand blaster or some form of chemical etching process to prevent leakage current to ground.
For the TSP assembly, RBD Instruments sells a variety of products to rebuild this assembly or you can even buy a complete assembly with or without exchange.
Clean the shields using the above process described for cleaning the ion pump well (using the wire brush, vacuum, and isopropanol).
Change the ion gauge filament, or if it’s in bad condition, replace the entire ion gauge. Keep in mind that RBD Instruments, Inc. sells ion gauge filaments and brand new assemblies as well.
Step 6: Reassembly
Tools required: 100 ft/lbs torque wrench
New parts required: New copper gaskets for all conflate flanges.
Note: RBD Instruments, Inc. sells every size of copper gasket that you could ever need for a PHI vacuum chamber. This includes the sizes that you will need to reassemble this chamber: 2.125”, 2.75”, 3.375”, and last but certainly not least is the 12.995” copper wire gasket that is used to mate the two halves of the vacuum chamber together.
Install the high voltage feedthru flange.
Install the new or rebuilt ion pump elements.
Install the Cryo shielding.
Install the TSP assembly.
Install the TSP shield.
Install the scissor jack assembly and hardware.
Install the poppet valve crank.
Install the poppet valve. (First clean it if necessary, also remove and clean the O-ring, use a small amount of high vacuum grease on the O-ring before you put it back in the groove).
Install the ion gauge.
Install a 12.995” copper wire gasket on the flange that mates the lower half of the vacuum chamber to the upper half. When replacing the wire gasket it is important to exercise patience. The removal of the old one can be easy, but you will likely find that the new gasket is rather hard to put into place. We have found that working the wire gasket around the flange with the handle end of a screw driver can work well to get the wire gasket to stretch into place onto the flange. You will see that it works a lot like putting a bike tire back on its rim, only in this case the material is copper and not rubber.
With the lower half reassembled and the 12.995” copper wire gasket in place it’s time to position the top half of the chamber into place. When tightening down this flange it is good to go slowly and to use a torque wrench. The maximum torque on this flange should be 50 ft/lbs. We recommend starting at 25 ft/lbs and working your way to 45 ft/lbs in 10 ft/lbs increments. The last tightening will be 50 ft/lbs.
That’s it! Time to start roughing the chamber down with your turbo and roughing pump.
After a number of years it becomes necessary to replace the ion pump elements used on surface analysis instrumentation such as X-ray Photoelectron spectrometers (XPS), Auger (AES), and Secondary Ion Mass spectrometers (SIMS). But what if you can’t afford the cost of new ion pump elements? Depending on how worn out the plates are, you may simply be able to “flip” the plates.
This procedure is written for the DI (Differential Ion) pump elements used on most PHI surface analysis and Perkin Elmer vacuum systems. However, it can also be applied to other ion pump elements such as Varian, which are used on many general-purpose vacuum systems.
Ion pump elements have three basic components: magnets, an anode, and two cathodes. For the DI pumps, one cathode plate is made out of tantalum and the other cathode plate is made out of titanium. Using cathodes made from these two materials provides good pumping stability for both inert and active gases. The size of the pump is determined by the number of elements used. For example, a Perkin-Elmer 120 l/s ion pump has 4 elements and a 220 l/s ion pump has 8 elements.
Ion pump element
The magnets cause electrons, which are created as part of the ionization process, to spiral in the anode. This in turn increases the probability of a collision with a gas molecule. When an electron collides with a gas molecule, the gas becomes ionized and the molecule is accelerated into a cathode. Over time, the cathodes become sputtered away and the ceramics that isolate the anode become coated and conductive. Also, flakes can form and accumulate, which can cause arcing from the anode to ground. As a result, the pump elements’ performance is greatly reduced and the elements need to be removed and inspected.
Usually, the pump elements need to be replaced. However, if the plates are not sputtered all the way through, it is possible to simply “flip” the plates, clean the anode, and replace the anode-isolation ceramics. Functionally, the ion pumps will be good as new. They will not last as long as new ion pump elements because the plates will not be as thick as new elements. You can, though, often get an extra 2-to-5 years of usage from the elements depending on your base vacuum, gas load, etc.
In the image below, you can see the anode, cathodes, and the heavily coated anode-isolation ceramics. Before you disassemble the elements, make a note of the position of the anode tab. One of the elements usually has the tab on the opposite side from the others. You will reassemble the elements so the tab is in the same location.
Coated ion pump element
Disassembling and Reassembling the Ion Pump Elements
Wear gloves and use clean tools when disassembling and reassembling the ion pump elements.
Use a slotted screwdriver and a 5/16″ open end wrench to remove the screws and nuts that hold the elements together. TIP: Use isopropanol as a lubricant to prevent the nuts from seizing.
Use a small flat-tip screwdriver and a pair of pliers to bend the ceramic shield tabs up.
Lift each ceramic shield out of its support bracket to remove the anode-isolation ceramics.
The graphic below shows the components once the pump elements have been disassembled: the anode plate, the cathode plates, and the support brackets
The image below shows the cathode after it has been sputtered. The sputtered areas look like pin holes. In this example, the sputtering is only about ½ of the way through the plate, which means that there is a lot of material left.
Sputtered ion pump cathode plate
As shown in the picture below, we can see that the cathode is not sputtered all the way through when we flip it over; there are no holes on this side of the cathode. Because the center of the sputtered area will most likely not line up perfectly when the plate is flipped, the lifetime of the pump will be extended.
Un-sputtered ion pump cathode
The picture below is an example of a plate that is sputtered all the way through. In this case, the ion pump elements need to be replaced and not rebuilt.
Sputtered ion pump cathode
The picture below shows a clean ceramic and a coated ceramic. RBD Instruments provides the new ceramics. Please visit the Parts – Vacuum related section of our website at www.rbdinstruments.com.
Ion pump ceramics
Once you have disassembled the elements, the rebuild procedure is very simple:
While wearing gloves, use a clean wire brush to remove any flakes from the plates, anode, support brackets, and ceramic shields. Note that you do not need to remove all of the deposits and discoloration on the parts. Just make sure that whatever remains will not come off easily. The important thing is that the active portion of the plates is now fresh, the ceramics are new, and there are no loose flakes that can cause shorting.
Install new ceramics. TIP Use a channel lock pliers to crimp the tabs on the ceramic shields that hold the ceramics in place.
Flip the plates so that the fresh side is facing the anode. Because the tantalum plate is thinner the titanium plate, most elements will have a thin steel plate on the tantalum side of the cathode. The tantalum plate will be noticeably heavier than the steel plate.
Make sure that you put the clean tantalum side towards the anode. The picture below shows the dirty element after the plates have been flipped and reassembled. It may not look pretty, but it will work as well as a new element.
Rebuilt ion pump element with flipped plates
Assemble the plates and support brackets, as shown in the picture above. Make sure that the support brackets are holding the anode snuggly as you tighten the screws and nuts.
Installing the Elements Back into the Pump Well
Before installing your rebuilt or new ion pump elements, use a wire brush and a vacuum cleaner to clean the pump well and remove all flakes that are inside the pump well. You can also wipe the inside of the pump well with a Kim wipe or lint-free cloth and some isopropanol. You want the pump well to be as clean as possible as any remaining flakes can cause shorting in the elements, which would require that you disassemble the ion pump again.
If possible, bake your vacuum chamber into the turbo pump for 4 hours.
Let the ion pump cool down before you try to start the ion pumps. Removing as much water vapor as possible will make the ion pumps much easier to start.
Start the ion pump.
Pump the chamber until you are in low 10-7 or low 10-8 Torr range.
With the ion pumps on, bake the chamber again for an additional 8-to-24 hours.
If you need more information on this procedure or would like to order the ceramics or new ion pump elements, please contact us at firstname.lastname@example.org or call us at 541-550-5016
Here are some pictures that show an ion pump being lowered: