A brand new cryopump system with compressor, pump and lines is a clean system from the factory.  Austin Scientific evacuate the lines, pump and compressor before backfilling with five nines (99.999% pure) helium.  Over time (usually a few years), water vapor and air gases will evolve from the system itself - there are metals, welds, brazes, o-rings in all the components of the system, all sources.  There is the possibility of introducing air gases when the individual components are connected, disconnected, stored etc.  Also, if the flat gasket that is on the male aeroquip becomes lost or damaged after some connections and reconnections, there is the possibility of introducing air gases into the helium stream by venture action of the high pressure helium coursing through the system.

If the amount of water vapor, O2, N2 reaches a certain value, when it freezes in the cryopump coldhead it will interrupt the smooth action of the reciprocating displacers in the coldhead.  Many standard CTI Cryotorr ® pumps and ALL Austin Scientific cryopumps have a sight-glass where one can see the motor turning.  The term for the ‘grinding' noise you can hear is RATCHETING - the motor drive bearing seen in the sight glass will hesitate at the '10 o'clock' position before continuing for another cycle (to hesitate again). 

There are degrees of contamination - in most cases a helium purge (when the pump is at room temperature) can drive out the moisture and the pump can continue.  In other cases, there can be extreme water vapor contamination (when the displacers are removed, there is liquid water on the displacers).  The displacer material is hygroscopic and will swell, sometimes enough to seize the displacer in the cylinder and stop the motor.  Most cryopumps have a two stage stepper motor that is quite powerful - in some cases (especially CP-10 with the larger motor), there is a good possibility of breaking the motor shaft.

There are many variables in the answer to this question.  Generally, a cryopump should last between 3 and 5 years before needing a rebuild.  If the system is clean (no contaminants in the helium stream), the pump will last until the various seals wear and helium blow-by makes the pump lose efficiency and unable to reach the temperatures required for processing.  On the vacuum side of the pump, it will pump well until the charcoal array is contaminated and becomes unable to pump and hold hydrogen (or in some cases like ion implant - residue from the process will contaminate the inlet array, interfering with water vapor pumping).

Over time, the first and second stage seals will wear - the inlet and exhaust valve bodies will wear, as will the kap seal gland that the scotch yoke rides through.

When the seals wear, the temperature of the pump will rise over time - different applications may require different acceptable temperatures for processing.

But what about the vacuum side of the pump?

The life of the vacuum side of the pump is extremely process dependant.  A research student in a university who processes occasionally and has a chamber that stays for a long time in the 10e-9 torr range is not introducing many contaminants into the pump.  The charcoal array could stay clean for a long time, beyond the time that the helium side will need rebuild.

On the other hand, an ion implant user has a process that puts lots of contaminants into the pump - basically, the inlet array becomes a ‘gooey mess'.  This can happen within six months, well before the mechanical side of the pump shows wear.

Most vacuum processes using cryopumps fall between the two extremes.

Yes, the vacuum side rebuild can easily be done by the customer - with instructions and following some easy procedures.  We sell array kits that include latex gloves, the arrays, new hardware (nuts, washers), the tool for disassembly, new indium pre-cut gaskets and instructions.

The simple answer is that yes, it is quite possible to rebuild (refurbish etc.) the vacuum side of the cryopump - replace the charcoal array, clean or replace the inlet array and radiation shield.

BUT - the helium side is a different matter, a full rebuild requires fully qualified technicians with special tools to replace bearings, bushings, seals etc.  Austin Scientific do sell a minor rebuild kit where a trained, qualified technician can effect a minor rebuild that doesn't disturb the timing - this entails replacing motor bearings, drive and valve bearings, first and second stage seals and all o-rings that are removed.

The frequency of rebuilding the complete pump depends upon the duty cycle, the cleanliness of the system (insofar as the helium stream through the pump and compressor is concerned).  The vacuum side cleanliness depends on the process, the gases used, the cleanliness of the chamber and valves themselves.

In some processes, such as ion implant, there is a great deal of residue from the photo resist that gets into the pump, requiring maybe more than one vacuum side rebuild before the helium side needs attention. 

The Austin Scientific standard rebuild procedure replaces almost all of the internal parts of the pump.  We replace both displacers, first and second stage seals, inlet and exhaust valve bodies, all bearings, bushings, o-rings - basically everything except the hardened steel scotch yoke and valve stems. 

Austin Scientific is quite willing to teach customers the vacuum side rebuild procedure for pumps.  Often, the vacuum in the chamber deteriorates well before the helium side needs a rebuild and the customer can drop the pump, change and clean the arrays and place the pump back in service within a few hours.

For advice on whether it is time to rebuild the pump, please call 512 441 6893 and ask for customer service.