System for Managing a Cleanroom Environment

Abstract

A system for managing cleanroom resources by providing a number of critical features in an integrated, low-cost package is described. The critical features include monitoring and recording cleanroom environmental conditions such as temperature, humidity and room differential pressure, notifying users of alarm situations when cleanroom environmental conditions fall outside predetermined limits, and reducing cleanroom energy usage by turning off HEPA filter fan units (FFUs) and cleanroom lights when they are not needed.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional application 61/870,159 filed 26 Aug. 2013 which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to means for monitoring and recording cleanroom environmental conditions while providing warning messages in various formats if the environmental parameters depart from preset limits. The system also provides a means for optimizing cleanroom energy consumption.

2. Related Background Art

Cleanrooms are specially constructed, environmentally controlled enclosed spaces where extensive measures are taken to eliminate airborne particulates. Cleanrooms may also exhibit tight controls on temperature, humidity, air pressure, airflow patterns, air motion, vibration, noise, viable (living) organisms, and lighting, but the primary design objective of a cleanroom is particulate control. The term “particulate control” applies to controlling the concentration and dispersion of both particulate and microbial contamination within the enclosed space. A cleanroom is defined in the International Organization for Standardization (ISO) standard 14644-1 as a “room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation and retention of particles inside the room and in which other relevant parameters, e.g. temperature, humidity and pressure are controlled as necessary.”

Today, many manufacturing processes require spaces in which particulate and microbial contamination are tightly controlled while maintaining reasonable installation and operating costs. Clean rooms are typically used in manufacturing, packaging, and research facilities associated with the following industries:

1. Semiconductor: This industry drives the state of the art clean room design, and this industry accounts for a significant number of all operating clean rooms.

2. Pharmaceutical: Clean rooms control living particles that would produce undesirable bacterial growth in the preparation of biological, pharmaceutical, and other medical products as well as in genetic engineering research.

3. Aerospace: The manufacturing and assembling of aerospace electronics, missiles and satellites were the first application of clean rooms. Large volume clean room spaces with extreme cleanliness are involved.

4. Miscellaneous Applications: Other uses include advanced materials research, laser and optic industries, microelectronics facility, paint room and in some aseptic foods production, also in some high infection risk areas of hospitals. While hospital operating rooms can be considered clean spaces, their concern is to control the types of contamination rather than the quantity of particles present.

The sources of particulate contamination are generally categorized as either external sources or internal sources. For any given space, there exists the external influence of gross atmospheric contamination. External contamination is brought in primarily through the air conditioning system through fresh air. Also, external contamination can infiltrate through building doors, windows, cracks, and wall penetrations for pipes, cables and ducts. The external contamination is controlled primarily by using high efficiency filtration such as high efficiency particle air (HEPA) filters, by providing positive pressurization of the cleanroom relative to external spaces to prevent the admission of external contaminants, and rigorous sealing of potential penetrations into the cleanroom space.

The largest potential internal source of contamination is the clean room workforce. Other sources are the shedding of surfaces, process equipment and the process itself. People in the workspace generate particles in the form of skin flakes, lint, cosmetics, and respiratory emissions. Industry processes generate particles from mechanical friction between moving parts, combustion processes, chemical vapors, soldering fumes, and cleaning agents. The size of these particles ranges from 0.001 microns to several hundred microns. Particles larger than 5 microns tend to settle quickly unless disturbed by moving air. The greatest concern is that a particle deposits on the product causing contamination or defect.

Particulate control is primarily achieved through airflow design. In essence, filtered and conditioned air is passed through the enclosed room space at a rate sufficient to sweep any internally generated particles out of the space to be trapped in external filters before contamination of the work product can occur. This often requires that the total volume of cleanroom air be changed many times per hour. The cleanroom industry specifies the cleanliness of rooms by referring to class numbers. Federal Standard 209E, “Airborne Particulate Cleanliness Classes in Clean Rooms and Clean Zones”, Sep. 11, 1992, categorizes clean rooms in six general classes, depending on the particle count (particles per cubic foot) and size in microns. These classes are listed in Table I along with the typical number of room air changes per hour and typical air flow rates required to sustain them.

TABLE I
Cleanroom Classes
	Maximum allowable count per	Air	Air
	cubic foot of air	Changes	Flow
Room	Particle size (microns)	per	(cfm/
Class	0.1	0.2	0.3	0.5	5	Hour	sq. ft.)
1	35	7.5	3	1	0	600	100
10	350	75	30	10	0	540	85
100		750	300	100	0	480	75
1,000				1,000	7	180	25
10,000				10,000	70	60	10
100,000				100,000	700	20	1

The air flow requirements shown in Table I have significant implications on the amount of energy needed to operate a cleanroom. In their paper “Cleanroom Energy Optimization Methods,” presented at the Fourteenth Symposium on Improving Building Systems in Hot and Humid Climates held in Richardson, Tex. May 17-20, 2004, authors Schrecengost and Naughton summarized several studies on energy use in cleanrooms used in the semiconductor industry. They reported that up to 42% of the total non-process related energy consumption (i.e., not related to the operation of manufacturing equipment within the cleanroom) was related to operation of the recirculation fans required to maintain adequate air flow rates through the cleanroom to establish the desired class of particulate control. More than 50% of the total non-process related energy consumption was related to operation of the air-conditioning systems required to maintain the required temperature and humidity levels of the cleanroom air supply. Although the large cleanrooms used in semiconductor manufacturing operations are typically used 24 hours per day, 7 days per week, it is not uncommon for small and mid-sized cleanrooms operated in other industries to be unused at night and on weekends, although the cleanroom systems typically remain in operation to prevent particulate contamination during the off hours. Thus, a need exists for a cleanroom resource management system to allow reduced energy consumption during evening and weekend hours without compromising the environmental integrity of the cleanroom space.

DISCLOSURE OF THE INVENTION

The present invention provides a system for managing cleanroom resources by providing a number of critical features in an integrated, low-cost package:

1. monitoring and recording cleanroom environmental conditions such as temperature, humidity and room differential pressure,

2. notifying users of alarm situations when cleanroom environmental conditions either exceed or fall below predetermined limits, and

3. reducing cleanroom energy usage by turning off HEPA filter fan units (FFUs) and cleanroom lights when they are not needed.

In a separate embodiment, user notification can be provided to a list of selected users via telephone or internet communications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the two primary configurations for achieving a unidirectional airflow type of cleanroom.

FIG. 2 is a diagram showing the primary electromechanical systems used in a cleanroom.

FIG. 3 shows a typical cleanroom configuration using filter fan units (FFUs).

FIG. 4 is a diagram showing a prior art monitoring and control system.

FIG. 5 is a diagram depicting a typical prior art monitoring and control system graphical user interface.

FIG. 6 shows airflow configurations for a fully powered and partially powered cleanroom.

FIG. 7 is a diagram depicting an embodiment of the present invention cleanroom monitoring and control system.

FIG. 8 is a diagram depicting an embodiment of the present invention monitoring and control system graphical user interface.

FIG. 9 is a diagram depicting an embodiment of the present invention monitoring and control system graphical user interface for multiple cleanrooms.

DETAILED DESCRIPTION

The features of the present invention are set forth in the appended claims which may be best understood by reference to the following description taken in conjunction with the accompanying drawings.

Cleanrooms have evolved into two major types differentiated by their method of ventilation: unidirectional airflow and non-unidirectional airflow cleanrooms. Unidirectional airflow cleanrooms are characterized by a design that attempts to maintain airflow at a constant level throughout the cleanroom. In non-unidirectional airflow cleanrooms, the airflow is constant only over a limited work area within the cleanroom, and is allowed to diminish elsewhere within the cleanroom. Unidirectional airflow cleanrooms are generally required to achieve the lowest cleanroom classes. FIG. 1 depicts the two basic configurations used to achieve unidirectional airflow cleanrooms. FIG. 1A shows a cleanroom 100 wherein conditioned air 101 is pressurized by a single large fan 102 and is directed into the cleanroom through contiguous HEPA filter units 103 resulting in a uniform airflow 104 throughout the cleanroom. In this example air exits the cleanroom through a perforated floor 105 and is extracted 106 for recirculation. FIG. 1B shows an alternate configuration using HEPA filter fan units (FFUs) 107 wherein fans are incorporated within the HEPA filter housings to partially pressurize the cleanroom. FFUs also typically contain integrated diagnostic sensors that provide feedback on their operating condition. FFUs are advantageous in that they provide for greater flexibility in the cleanroom configuration and require simpler housings than the single fan, however they are not capable of providing the static pressure levels that can be achieved using a single large fan. In the past, FFUs were generally less efficient than the dedicated single fan unit, but their popularity has stimulated significant efficiency improvements. Reducing the energy consumption of the single fan requires the use of an expensive, high power controller module to reduce fan speed and the air flow within the cleanroom remains uniform. However, smaller individual control units can be applied to control individual FFUs, allowing selected units to remain operating at full speed to protect critical work areas.

FIG. 2 is a diagram showing the primary electromechanical systems used in a cleanroom wherein FFUs are employed to establish a unidirectional airflow configuration. As in FIG. 1, supply air 101 is furnished to FFUs 107 which establish a unidirectional airflow 104 within the clean room. Air is extracted through openings in the floor 105 or sidewalls (not shown) and return air 106 is partially exhausted 204 outside the building using exhaust fan 203 and partially recirculated 205 to HVAC unit #2 200 for recirculation. Fresh air 202 from outside the building is separately conditioned by HVAC #2 201 and combined with the conditioned recirculated air. Optionally, separate fans in units HVAC #1 201 and HVAC #2 200 can be employed to prepressurize the supply air 101 in order to achieve the overall desired room pressurization. Fresh air 202 is required to compensate for the extract air 204 and the inevitable cleanroom leakage 206.

FIG. 3 shows a typical cleanroom configuration using FFUs. Cleanroom 300 incorporates window units 301 for visibility and six FFUs: FFU1 302, FFU2 303, FFU3 304, FFU4 305, FFU5 306 and FFU6 307. Supply air 101 enters the FFUs from the HVAC units and return air is extracted either through the floor or the walls (not shown.) The cleanroom also has three lighting units L1 308, L2 309 and L3 310. Subsequent discussion of cleanroom management systems will use this configuration as an example.

FIG. 4 is a diagram showing a prior art monitoring and control system. In this system, a personal computer (PC) 400 executes a monitor and control program that is used to receive and display cleanroom environmental parameters from various sensors, and to manually control the FFUs and room lights. Cleanroom environmental sensors for temperature 401, humidity 402 and room differential pressure 403 provide either analog or digital electronic signals that are directed to the PC 400 on sensor bus 404. Diagnostic signals 405 from FFUs 302-307 are directed to the PC 400 on FFU input bus 406. These sensor signals are monitored and displayed by the program executing on PC400 and audible and visible warning messages are displayed if the environmental parameters or FFU operational parameters exceed or fall below preprogrammed limits. Lighting control signals 408 are applied through the lighting output bus 407 to control digital switches 410 that connect power lines 409 to cleanroom lights 308-310 to the power mains 411. The speed of each of the FFU fans is controlled by FFU control signals 413 on the FFU output bus 412 that connect FFU power lines 415 to variable frequency motor drives 414. Lighting control and FFU speed control are effected by inputs to the program executing on PC 400.

FIG. 5 is a diagram depicting a typical prior art monitoring and control system graphical user interface (GUI) 500 as would be displayed continuously during cleanroom operation on PC 400 in FIG. 4. Multiple users who have been trained and qualified to manage cleanroom operations login to the program using preestablished usernames 501 and passwords 502. Cleanroom environmental conditions corresponding to temperature 503, humidity 504 and differential pressure 505 are shown on the graphic displays in the center of the GUI. Optionally, upper and lower setpoints can be entered for each of these quantities through pop-up menus accessed by clicking on an icon and audible and visible alarms triggered if operating conditions drift out of range. The status of each of the FFUs is shown in the graphic displays 506-511 at the left. Each of the FFU displays shows the unit number 512 and a status description (Normal, Off or Alarm) 513 as well as the current set point 514 and indicators for power 515 and alarm condition 516. All of the cleanroom parameter values in displays 503-511 are recorded with a time stamp on the PC 400 hard drive at predetermined intervals. Also displayed on the GUI are a scrolling history of alarm conditions 517 and a related action log 518 that provides traceability for actions associated with the alarm history 517.

Although the system depicted in FIGS. 4 and 5 functions adequately in managing cleanroom resources, it exhibits several deficiencies that are addressed by the present invention. In one aspect, the variable frequency motor drive units 414 used to adjust FFU fan speeds are expensive and represent a potential reliability risk. It is much more economical and reliable to employ simple digitally controlled electrical switches to shut off selected FFUs. FIG. 6A shows a cross section of the example cleanroom 300 shown in FIG. 3 wherein all FFUs 302-307 are powered resulting in the desired unidirectional airflow configuration 104 supported during work hours. FIG. 6B illustrates the airflow configuration 600 that results when the outside FFUs 302, 303 and 306, 307 are powered off. The airflow configuration is now non-unidirectional, which would be unacceptable during normal working hours, but may be adequate during off hours, particularly if any work-in-progress (WIP) 601 stored within the cleanroom is located beneath the active FFUs 304, 305.

FIG. 7 is a diagram showing an embodiment of the present cleanroom monitoring and control system. As in the system of FIG. 4, a personal computer (PC) 400 executes a monitor and control program that is used to receive and display cleanroom environmental parameters from various sensors, and to control the FFUs and room lights. Cleanroom environmental sensors for temperature 401, humidity 402 and room differential pressure 403 are complemented with an optional particle counter 701 and each provide either analog or digital electronic signals that are directed to the PC 400 on sensor bus 404. Diagnostic signals 405 from FFUs 302-307 are directed to the PC 400 on FFU input bus 406. These sensor signals are monitored and displayed by the program executing on the PC 400 and audible and visible warning messages are displayed if the environmental parameters or FFU operational parameters exceed or fall below preprogrammed limits. In this embodiment, PC 400 is connected to the Internet 702 through a firewall 703 thereby allowing warning messages to be communicated to a predetermined list of recipients using telephone messaging, text messaging or e-mail messaging. Lighting control signals 408 are applied through the lighting output control line 407 to control digital switches 410 that connect power lines 409 to cleanroom lights 308, 310 to the power mains 411. Note that cleanroom light 309 is hardwired to be powered at all times. The FFU fans for FFUs 302, 303 and 306, 307 are controlled by FFU control signals 413 on the FFU output control line 412 that connect FFU power lines 415 to digital switches 410. Note that FFUs 304, 305 are hardwired to be powered at all times. Lighting and FFU power control are effected by inputs to the program executing on PC 400.

FIG. 8 is a diagram depicting an embodiment of the present monitoring and control system graphical user interface (GUI) 800 as would be displayed continuously during cleanroom operation on PC 400 in FIG. 7. As in FIG. 5, multiple users who have been trained and qualified to manage cleanroom operations login to the program using preestablished usernames 501 and passwords 502, and cleanroom environmental conditions corresponding to temperature 503, humidity 504 and differential pressure 505 are displayed. Optionally, upper and lower setpoints can be entered for each of the environmental quantities through pop-up menus accessed by clicking on an icon and audible, visible, and, optionally, electronic messaging alarms triggered if operating conditions drift out of range. The preprogrammed alarm threshold values for the room condition sensors are also displayed 809. Since the FFUs are not individually programmed, individual FFU icons are not needed. All of the cleanroom parameter values in displays 503-505 and 809 are recorded with a time stamp on the PC 400 hard drive at predetermined intervals. The status of the Energy Saver feature 801 appears in the center of the GUI which powers off the designated FFUs 302, 303 and 306, 307 and the designated cleanroom lights 308, 310 according to the schedule 802. Schedule parameters 802 can be set by clicking button 803. The Energy Saver mode can be enabled and disabled by clicking button 804. The present state of the Energy Saver feature is indicated by the position of icon 805 either over the “100% On” or over the “Saving Energy” schedule segments. Also displayed on the GUI is a scrolling action log 518 that provides traceability for actions associated with the Energy Saver settings 801.

In many instances, a manufacturing facility may comprise a number of separate mini-cleanroom units for individual specific manufacturing processes, each requiring independent control and monitoring of its environmental conditions. FIG. 9 shows a GUI 900 for an alternate embodiment of the present monitoring and control system wherein the sensor bus 404 shown previously in FIG. 7 directs sensor signals from multiple rooms to the controlling PC 400. Although all of the sensor signals are continuously monitored by the program executing on the PC 400, the GUI 900 displays the room conditions 901 and alarm thresholds 902 for one specific room selected by means of a Room Selector submenu 903 on the GUI.

In a further embodiment of the monitoring and control system (not shown) the monitoring and control program executing on PC 400 and the GUI 900 include the means for controlling and displaying the status of the Energy Saver Mode for the selected room.

The present invention has been described in terms of the preferred embodiment and it is recognized that equivalents, alternatives and modifications, beyond those expressly stated, are possible and are within the scope of the attached claims.

Claims

1. In a cleanroom unit comprising an enclosed space supplied with conditioned air characterized by its temperature, humidity and differential pressure through electrically powered HEPA filter fan units and illuminated by electric lights, a system for managing cleanroom resources by a user comprising:

a. means for monitoring and recording said cleanroom air characteristics comprising: i. an electronic temperature sensor located within said cleanroom, ii. an electronic humidity sensor located within said cleanroom, iii. an electronic room differential pressure sensor located within said cleanroom, and iv. a personal computer having a graphical user interface executing a cleanroom control system program, said personal computer receiving electronic signals from said electronic temperature, humidity and pressure sensors and providing electronic control signals for said HEPA filter fan units and said electric lights;

b. means for setting predetermined limits within said cleanroom control system program executing on said personal computer that establish an acceptable range of electronic signals from said temperature, humidity and pressure sensors;

c. means for notifying said user of alarm situations when said cleanroom air characteristic sensor signals fall outside said predetermined limits through the graphical user interface of the cleanroom system control program executing on said personal computer;

d. means for setting predetermined schedules for application of said control signals for said HEPA filter fan units and said electric lights; and

e. means for reducing cleanroom energy usage by controlling the electrical power applied to said HEPA filter fan units (FFUs) and said electric lights in response to said control signals provided by the cleanroom system control program executing on said personal computer.

2. The cleanroom management system of claim 1 wherein the means for monitoring and recording cleanroom air characteristics further includes an electronic particle detector.

3. The cleanroom management system of claim 1 wherein the means for notifying said user of alarm situations includes telephone messaging, text messaging, and e-mail messaging by the cleanroom system control program executing on said personal computer.

4. The cleanroom management system of claim 1 further comprising means for monitoring and recording, setting predetermined limits, notifying the user, setting predetermined schedules, and reducing cleanroom energy usage for a multiplicity of individual cleanroom units.