EP0994031A1

EP0994031A1 - Process for producing an item for a sterile environment

Info

Publication number: EP0994031A1
Application number: EP98650068A
Authority: EP
Inventors: Thomas Comerford; Patrick Joseph O'mahony
Original assignee: Comerford O'mahony developments c/o OMC Engineering
Current assignee: Comerford O'mahony developments c/o OMC Engineering
Priority date: 1998-10-14
Filing date: 1998-10-14
Publication date: 2000-04-19
Anticipated expiration: 2018-10-14
Also published as: DE69822831D1; EP0994031B1

Abstract

A stainless steel item for a sterile environment is produced by fabrication, pickling, polishing, drying, final cleaning in a cleanroom, first packing in the cleanroom, and second and third packing in an environmentally-controlled packing room. The cleanroom has an environment maintained at a sterility level at least matching that of the destination, such as a health care product production facility. Therefore, the item may be shipped directly to the facility and gradually have the packaging layers removed to allow direct installation. Contamination arising from fabrication and shipping is avoided and there is no need for cleaning at the destination facility.

Description

The invention relates to a process for producing items of equipment for use in a sterile environments such as semiconductor wafer or health care product production facilities.
The sterility requirements for items in such environments is well documented. One of the major problems in maintaining such an environment is that of introducing new items such as production workstations, robotic handlers, conveyors etc. Because such items are initially foreign to the sterile environment, they are a major potential source of contamination. Agents such as siloxanes, silicones, chlorides, and sulphates are particularly dangerous in electronic production environments. Agents such as micrococci, spores, streptococci, pseudomonas, gram rods, and sharps are particularly dangerous in food and health care production environments. Items introduced into sterile environments may carry these agents on their surfaces. Also, they may outgas over time, thereby contaminating the environment well after initial installation.
Heretofore, the approach to production of such items of equipment has been to fabricate close to the site and introduce the item into the environment and clean it using the cleaning agents for the existing equipment in the environment. This is a difficult task to perform because the cleaning must deal with a wide range of types of contamination which arise during production, transport, and final assembly and installation. These are different in nature from those which arise in the sterile environment.
According the invention there is provided a process comprising the steps of:-
fabricating the item from stainless steel;
polishing the item;
drying the item with filtered hot air;
transferring the item to a cleanroom, in which the environment is controlled to a specification equalling or exceeding that of the sterile environment to which the item is to be shipped cleaning the item with a cleaning solution, and subsequently packing the item in a first packaging layer of a non-outgassing polymeric material which is free of plasticiser and polysilicates: and
transferring the packed item to a controlled packing room, and packing it with a second packaging layer.
Therefore, the invention in a very simple manner provides for modular production of an item because all fabrication and sterility operations are dealt with at the one location and the item may be shipped directly to any destination facility. Installation work at the facility is greatly reduced and the producer has control of the sterility standard achieved.
In one embodiment, the process comprises the further step of packing the item with a third packaging layer in the controlled packing room. This provides an additional level of protection to ensure sterility.
Preferably, the cleanroom air is pumped through a pre-filter and subsequently through a HEPA filter. In one embodiment, input air to the pre-filter is a combination of external air and re-circulated air, and the pre-filter includes chemical adsorption filtration media. Preferably, the proportion of external air is approximately 10% by volume. It has been found that this provides a particularly consistent sterile environment.
In one embodiment, the re-circulated air is pumped through low vents into air walls, upwardly through the air walls and overhead into the pre-filter.
In another embodiment, the polishing step comprises the sub-steps of pre-cleaning descaling, electropolishing, passivation, sodium bicarbonate flushing and deionised water rinsing.
Preferably, the electropolishing is performed with phosphoric, sulphuric, and organic solutions.
The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings, in which:-
Fig. 1 is a diagrammatic plan view of a production process of the invention;
Fig. 2 is a flow chart illustrating one part of the process in more detail;
Fig. 3 is a diagrammatic elevational view of a cleanroom used for the process; and
Figs. 4 and 5 are more detailed front and side views respectively of the cleanroom.
Referring to Fig. 1, there is shown a plan view of a production facility in which single lines indicate the production areas and double lines indicate process flow. The process of the invention produces stainless steel fabricated items for use in a sterile environment.
In step 2 the item is fabricated. An important aspects of fabrication is that consistent and accurate workplace fabrication is ensured by use of jigs. All tubes are bent using a mandril tube bender to minimise the number of welded joints. Welding is 100% and is free from pinholes to avoid electrolytes becoming trapped in joints.
In step 3 the item is treated in a pickling area in which nitric hydrofluoric acid is used at varying strengths according to time and oxide thickness. This area has negative pressure by action of an extraction unit.
The item is then polished in step 4 in a production area at atmospheric pressure. As described in more detail below, polishing involves the sub-steps of electropolishing, passivation, sodium bicarbonate flushing and dionised water rinsing.
Polishing ensures that minute particles introduced during the fabrication step 2 are eliminated. This is particularly important because these impurities may be fused during welding. Also, the fabrication step 2 may introduce contamination by:-
manual cleaning,
blast cleaning (which can induce particle inclusion which subsequently corrodes), and
burring of edges.
Referring to Fig. 2, polishing is described in more detail. In step 20, the item is pre-cleaned with an alkaline spray to remove any organic matter.
In step 21, the item is rinsed with deionised water.
In step 22, the item is descaled with nitric HF at a concentration of 6 to 25%. A particularly preferred concentration within this range is 15% Nitric Acid in 10% hydrofluoric acid.
The item is rinsed in step 23 with high pressure dionised water pumped as a power jet at 1400 kPa.
During the electropolishing sub-step 24, there are three phases as follows;-
an etching phase in which ions dissolve proportionate to free energy against a normal IR linear relationship,
a polishing phase involving formation of solid oxide film, and
a gassing phase in which there is oxygen evolution.
The electropolishing tank preferably includes 53% H₂SO₄, 22% H₃PO, 23% H₂O, 2% aniline. The temperature is maintained at 55°C. There is a low voltage DC supply providing a current of 10 to 50 A/dm².
In step 25 the item is rinsed with a power spray.
The item is passivated with 10 to 50% nitric solution in step 26. The preferred solution concentration is 20%. The passivation neutralises carbon elements which may have adhered to the tubes by dissolution in nitric acid.
In step 27 there is sodium bicarbonate treatment in which items are immersed in a 4% solution of this chemical and agitated so that the chemical passes through all the internal cavities.
The item is rinsed with deionised water in step 28 using a power jet delivering 1400 kPa.
The item is then dried in step 7 in a drying area maintained at a positive pressure.
Drying involves blowing hot air which has been treated to sub-micron filtration by use of HEPA filters.
In step 8, the item is transferred into a buffer area, which is also at a positive pressure relative to the previous area. The buffer area separates the drying area from a cleanroom, in which the item is cleaned and packed. The cleanroom is described in more detail below.
The drying step 7 is very important as it ensures that internal surfaces of the item such as the internal surfaces of tubes are thoroughly cleaned to the extent that they do not include residues arising from the polishing step 4. Transfer to the buffer area helps to ensure that the cleanroom is maintained according to a particular sterility specification
It has been found that by transferring the item directly to a separate drying area and drying it with hot air, the item has a high level of sterility before transfer to the buffer area. In particular, residues are removed without risk of corrosion.
Once in the cleanroom, the item is cleaned using laboratory grade isopropyl alcohol manually applied using cleanroom wipes selected to avoid particulate or outgassing residues.
Referring now to Figs. 3 to 5 inclusive, the cleanroom is now described in more detail. The cleanroom is indicated by the numeral 40 and it comprises an air inlet 41 which passes air though a pre-filter 42. The air is then distributed in a manifold which pumps it though HEPA filters 43 before it is directed downwardly into the space. The flow rate is 0.7 m/s. However, the flow rate may be in the region of 0.3 to 0.9 m/s. The air is directed though vents 44 and into vertical air walls 45 at each of the four sides of the cleanroom. The air is then directed back into the pre-filter 42. Approximately 90% of the air is re-circulated in this manner, the remaining 10% being introduced from the external environment. In the cleanroom, operatives are fully gowned and wear appropriate hoods and face masks to prevent fibres from deposition into the item. Thus, the cleanroom environment is at least as sterile as that of the facility to which the item is to be shipped, in this case Class 1000 sterility.
As the item is moved into the cleanroom, it is moved through an air lock and it is blown down by ionisation equipment. This achieves control over airborne fibres bonded by electrostatic force.
Chemical filtration media are used in the pre-filter to prevent ingress of trace ionic or organic airborne film into the cleanroom.
Solvent vapours are separately extracted by fans connected to adsorption filters.
An important aspect of the cleanroom operations is that after cleaning the item is immediately packed in non-outgassing polymeric material within a Class 1000 environment. Complex assemblies are also vacuum pack to ensure integrity. Packaging material is selected to be free of plasticiser and polysilicates. Sealing tapes are also free of solvents and volatile chemicals. Examples of packaging materials and tapes are cleanroom quality polypropylene and acrylic adhesive.
After transfer from the buffer area the item is packed with a second layer of packaging in step 10. While in the same area, the item is finally packed with a third packaging layer in step 11. These successive packing steps ensure that the item is encapsulated immediately after cleaning and that integrity of the packaging is maintained to the final destination. The material for the second and third packaging layers is impervious to airborne ingress or adsorption of organic or ionic matter. Suitable high density polypropylene film satisfies these requirements.
After final inspection in step 12, the item is shipped to the destination. At the final destination the procedure is to remove the third packaging layer and the second packaging layer in an area adjacent to the sterile environment. In the sterile environment, the first packaging layer is removed and there is no need to clean the item and it may be installed directly. Thus, the invention in a very simple manner allows sterility control at a central production location at which all of the fabrication, surface treating and sterility aspects are dealt with. This provides significantly improved control as there is no reliance on personnel or the environment at the destination.
The invention is not limited to the embodiments described, but may be varied in construction and detail within the scope of the claims.

Claims

A process for producing an item for a sterile environment, the process comprising the steps of:-

fabricating the item from stainless steel;

polishing the item;

drying the item with filtered hot air;

transferring the item to a cleanroom, in which the environment is controlled to a specification equalling or exceeding that of the sterile environment to which the item is to be shipped, cleaning the item with a cleaning solution, and subsequently packing the item with a first packaging layer of a non-outgassing polymeric material which is free of plasticiser and polysilicates; and

transferring the packed item to a controlled packing room, and packing it with a second packaging layer.
A process as claimed in claim 1, comprising the further step of packing the item with a third packaging layer in the controlled packing room.
A process as claimed in claims 1 or 2, wherein the cleanroom air is pumped through a pre-filter and subsequently through a HEPA filter, and wherein the item is moved into the cleanroom through an air lock.
A process as claimed in claim 3, wherein the input air to the pre-filter is a combination of external air and re-circulated air, and the pre-filter includes chemical adsorption filtration media.
A process as claimed in claim 4, wherein the proportion of external air is approximately 10% by volume.
A process as claimed in any of claims 3 to 6, wherein the air flowrate is in the range of 0.3 to 0.9m/s
A process as claimed in any of claims 4 to 6, wherein the re-circulated air is pumped through low vents into air walls, upwardly through the air walls and overhead into the pre-filter.
A process as claimed in any preceding claim, wherein the polishing step comprises the sub-steps of pre-cleaning descaling, electropolishing, passivation, sodium bicarbonate flushing, and deionised water rinsing.
A process as claimed in claim 8, wherein the electropolishing is performed with phosphoric, sulphuric, and organic solutions.
A stainless steel item whenever produced by a process as claimed in any preceding claim.