Performance Guidelines for Heated Vacuum Exhaust System

Straight Pipe Line
Reduce the Number of Fittings
Reduce the Number of Heat Sinks
Pipe Hangers
Identical Configurations
Clean Pipe
Leave Room
Valves
Pumps
Discharge Piping
Cold Traps

Even if you choose not to use Pyewch®, let us at least offer you a few suggestion for getting a job done right the first time.   For most of you in the industry this is probably review, but we might just have a tip or two that can save you a lot of headaches in the future.  

Straight Pipe Line:   Easier said than done, but route the vacuum piping as straight as possible.   TOP

Reduce the Number of Fittings:   Keep the number of 45° and 90° elbows to an absolute minimum.  Remember that 45° offers less resistance than 90°.   The American Vacuum Society (AVS) recommends only 270° of turn and a maximum 360° of turn on the foreline or exhaust line.   TOP

Reduce the Number of Heat Sinks:   Keep these to a minimum.  Remember every clamp, flange, and hangar becomes a potential heat sink that draws heat away from the pipe.  Yes, clamps and hangars can and should be heated, but placing them too close together or too frequently significantly hampers the ability to heat them properly.  TOP

Pipe Hangers:   Hangers are needed to hang your piping but again, isolate them from the unistrut and do not let adjacent hangers touch the pipe that is to be heated. On horizontal runs,  trapeze-type hangers are preferable and allow the placement of stainless steal pipe saddles to distribute the pipe weight along the length of the heater jacket.   Vertical runs of pipe require riser clamps with insulated isolation inserts and extra heat applied on both sides of the hanger.   TOP

Identical Configurations:   We recommend that wherever possible, configure the piping to your process tools as identically as possible.    We realize that this is wishful thinking in most fab environments, but whenever possible it is a good practice and in most cases can reduce the cost of multiple systems.   TOP

Clean Pipe:   Start with a clean piping system!   Do not install heater jackets on a system that is already full of contaminants.  Back streaming can and does occur.   This can significantly increase your risk of adding contaminates in process.   TOP

Leave Room:   We want to build a system that will really do the job for you!   If give us enough room for the heater jackets, the system will perform as designed and give you years of trouble free service.   However, having sections of pump line that touch one another or that touch adjacent walls and pipes leaves room for future problems.  So leave as much room as possible by planning ahead.   TOP

Valves:   Choose good valves!   Lawrence Livermore National Laboratories (LLNL) has done extensive research on the cleanest, most efficient valves for semiconductor use.   Do your homework and choose valves that are easy to heat and that do not add contaminates to the system.   TOP

Pumps:   Select pumps that are designed to maintain the vapor state of the effluent by-products by running hot.   There are several manufacturers that offer such designs.   Remember that good foreline heat protects the pump.   TOP

Discharge Piping:   If you heat the foreline piping from the process chamber to the vacuum pump, then you definitely need to heat the discharge line from the pump to the point of abatement.   By not heating this line, all you do is create a very long, hard to clean trap that cheats the abatement equipment from performing the task that it was purchased to do in the first place; namely, collect and/or incinerate the effluent by-products.   TOP

Cold Traps:   Yes, cold traps are partially effective.   They do collect by-product, but I have yet to see a system using cold traps that is completely devoid of contaminate downstream of the trap.  If you are using an abatement system, the goal should be to deliver all the effluents to this equipment.  TOP