How to verify ULPA low outgassing requirements?

The three words 'low outgassing' appear more and more frequently in procurement documents. Semiconductors, display panels, precision optics, pharmaceuticals - many processes have increasingly low tolerance for volatile organic compounds in the air. As a key component in the air supply path, filters are naturally included in the scope of control.

But 'low outgassing' itself is not an indicator that can be established alone. What it wants to answer is: what substance, under what conditions, and how much is released. If these three items are not clear, verification is impossible.

A common situation in actual projects is: the procurement document states 'low outgassing required', and the supplier replies 'our products are low outgassing'. Both parties think they have reached a consensus, but only after the acceptance check do they find that the 'low outgassing' they understand is not the same thing at all. Therefore, the first step in verification is not to find a detection method, but to write down the requirements clearly.

Let’s first clarify what “releasing” specifically refers to.

'Release' is a general term, and different projects focus on completely different goals.

Semiconductor processes typically focus on siloxanes, plasticizers, amines, acidic gases, etc. These substances may form films on the wafer surface or affect photoresist performance. Some projects will list specific target compounds, while others will give limits for total organic carbon (TOC) or total volatile organic compounds (TVOC).

Pharmaceutical and biomedical industries may be concerned with particulate matter and microorganisms, and the requirements for chemical outgassing depend on the specific process. If the aseptic filling area is sensitive to certain types of volatiles, corresponding control requirements will also be put forward.

Display panels and precision optics may be concerned with the impact of certain organic compounds on coatings or optical properties.

Different targets correspond to different detection methods and judgment standards. Generally speaking, 'low outgassing' means that the supplier cannot confirm what standards are used for testing, what substances are tested, and what the limits are. For specific verification methods, please refer to the relevant instructions of the technical agreement.

The testing conditions must also be clear. Temperature, humidity, contact time, and sampling methods all affect outgassing results. For the same product, the gas release volume at 25°C and 60°C may differ several times. The test conditions should be noted on the report. Outgassing data out of conditions cannot explain the problem.

The material range should cover the entire product

This is where things tend to go wrong the most.

You can’t just test the filter material. A ULPA consists of filter material, support layer, edge sealing glue, outer frame, sealing gasket, and packaging materials. Outgassing can come from any of these, not just the filter media itself.

Edge sealants are a common source. The colloid may release organic volatiles during the curing process or during long-term operation. The gas release characteristics of different colloidal formulations vary widely.

Gaskets and frame treatments are also included. Rubber or silicone gaskets may release siloxane; the coating, anodizing or passivation process of the metal frame may leave chemical residues.

The impact of packaging materials is easily overlooked. Cross-contamination may occur if the filter element comes into contact with packaging materials containing volatile substances during transportation and storage. Some projects require that packaging materials also be included in the outgassing evaluation.

Therefore, the test samples provided during verification should represent the entire product configuration to be supplied. If only a small piece of filter material is measured, the outgassing level of the entire product cannot be inferred. When making specific selections, please refer to the comparison instructions between glass fiber and PTFE filter materials. involving HEPA/ULPA air filters , same logic. Verification of

Test samples must be representative of actual configurations

The sample range of gas release testing directly determines whether the verification conclusion can be used.

The sample is still the whole piece. The filter material sample is convenient for laboratory testing, but it does not cover the colloid, seals and outer frame. The whole piece test is closer to the actual use state, but the test methods and equipment requirements are higher. Which method to use depends on the limits and testing conditions required by the project.

Sample status. Is it a brand new filter element that has not been installed, or is it in a state that has been running for a period of time? Some materials have high gas release in the initial stage and tend to stabilize after running for a period of time. If the project focuses on long-term operating status, the detection conditions should correspond to this.

Sampling location. Where and how the sample is taken affects the results. Whether it is the air outlet side or the air inlet side, the static state or the running state, all need to be clarified in the detection plan.

Choice of detection method. Thermal desorption-gas chromatography mass spectrometry (TD-GC-MS) is a common method for detecting the release of organic matter, but the sampling tubes, desorption conditions and databases may be different in different laboratories. If the project requires comparison of data from different suppliers, the testing methods should be unified. For specific testing items, please refer to the relevant instructions for factory testing.

Sample verification and batch consistency

After passing the laboratory test, how to ensure the consistency of the actual product?

Sample verification. For projects with strict gas release requirements, it is recommended to conduct sample verification first - make samples according to the entire configuration to be supplied, and test them under actual working conditions. After confirming that the outgassing level is within the limit, proceed to mass production.

First item confirmed. When mass production begins, the first piece is inspected to confirm that it is consistent with the sample. After the first piece is passed, subsequent products will be produced using the same process and materials.

Change management. If there are changes to the material supplier, colloid formulation, or production process, outgassing effects should be reassessed. It cannot be assumed that 'the material name is the same' means the gas release level is the same. For specific procedures, please refer to the instructions related to filter material batch changes.

Regular spot checks. For long-term supply projects, random inspections can be carried out according to the agreed period to ensure continued compliance with requirements. The frequency and items of random inspections are determined according to the risk level. involving The selection of ULPA ultra-high efficiency filter can be checked based on the process requirements.

Record retention. The sample information, test conditions, results and judgment conclusions of each test should be archived. These records will be used for subsequent audits or problem tracing.

Project judgment example

A semiconductor equipment project requires ULPA to meet low outgassing requirements, and the procurement document states that 'the outgassing volume meets industry standards.'

The supplier provided a TD-GC-MS test report of the filter material, which showed that the main volatile matter content was below the detection limit. The project team believes that the requirements are met and purchases in bulk.

After the equipment had been running for a period of time, trace amounts of siloxane contamination were detected on the downstream wafer surface. The investigation found that the source of the contamination was the sealing gasket - the gasket uses a conventional silica gel formula and releases siloxane at operating temperature, but this was not covered in the filter material test report.

Treatment method: Replace with a low outgassing gasket and redo the entire outgassing test to confirm that contamination no longer occurs.

The key point in this case is: the filter media report cannot represent the entire product. Outgassing may come from any one component and the scope of verification must cover the entire configuration. involving HEPA high-efficiency filter is the same. The selection logic of

Selection and Acceptance Checklist

About Aili Industrial’s gas release verification package

The key to low outgassing verification is to match the target object, material range and test conditions. These three items should be written clearly in the agreement stage, and there will be a basis for subsequent implementation.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For projects with gas release requirements, we can assist in checking the filter material type and entire material configuration based on process conditions, target object list, and installation requirements. When the filter is matched with equipment such as FFU and EFU, the material information and interface conditions can also be confirmed uniformly.

When enquiring, state the outgassing requirements, target object list and detection methods to help confirm the appropriate material solution and verification process. Specific verification shall be subject to the technical documents and test results confirmed by the project.