Which precision electronics and sensor packaging should be HEPA or ULPA?

Packaging workshops usually have an overall cleanliness level, but what really determines the yield is often not the average particle concentration of the entire workshop, but the air condition within a few dozen centimeters of the key workstations.。

Sensor chips, optical windows, gold wire bonding points, and MEMS structures are much more sensitive to particles than other areas of the workshop. If a particle of a few microns falls on the bonding area, it may cause virtual soldering or short circuit; if it falls on the surface of the optical sensor, it may directly affect the calibration results. Therefore, the first step in selection is not to ask 'should the packaging workshop use HEPA or ULPA', but to ask 'which work station, what particles, and how much risk'.

First identify which locations really need protection

Precision electronics and sensor packaging covers many processes, and the degree of particle impact varies widely.

Die bonding and wire bonding : The chip surface and pad are directly exposed, and particles falling on the bonding interface will affect the connection strength. Such workstations usually require local cleaning and protection.

Optical sensor packaging : Once particles are stained on the surfaces of lenses, filters, and photodiodes, it may cause abnormal dark current or imaging defects. Such applications are also sensitive to submicron particles.

MEMS and thin film sensors : Movable structures or thin film areas may fail due to particle adhesion, requiring higher control of particles.

Post-packaging inspection and testing : If the product has been packaged, the impact of particles will be relatively small, but there are still requirements for cleanliness near the probe card and test socket.

Not all processes require the same grade. Configuring the entire packaging line to the highest level is costly and does not necessarily solve key problems. A more reasonable approach is to classify workstations and concentrate resources on exposed areas.

How to choose between HEPA and ULPA

In local air supply units, HEPA and ULPA are common options. The selection is mainly based on particle sensitivity and process requirements.

H14 high-efficiency filter : There are clear requirements for the filtration efficiency of 0.3 micron particles. With reasonable air supply volume and air flow coverage, a local 100-level environment can be established at key workstations. In most precision electronic packaging stations, if the main control is micron-sized particles, H14 can usually meet the requirement. Specific products can be referred to Description of HEPA high efficiency filter .

U15 or U16 ultra-high-efficiency filter : If the process is sensitive to 0.1 micron-sized particles, or the project acceptance criteria clearly require lower penetration, ULPA can be considered. Optical sensors, certain MEMS packages, and scenarios with high defect rate requirements may be used. Product types can refer to ULPA ultra high efficiency filter。

But grade is not the only variable. The actual protection effect of a well-sealed H14 local air supply unit may be better than that of a poorly sealed U16. Airflow coverage, installation interfaces, and maintenance methods should all be considered together with the grade.

How to configure local air supply

Key workstations for precision electronic packaging usually use local air supply instead of relying on the entire clean room.

FFU form : If there is installation space above the workstation, it can be used The FFU fan filter unit provides partial unidirectional flow coverage. The filter element can be HEPA or ULPA, depending on the particle control objectives.

EFU form : If the protection area is inside the device, or the installation space is limited, it can be used EFU equipment side fan filter unit . This type of application needs to consider the equipment structure, moving parts and air supply path together. The thickness of the filter element and the disassembly and assembly method often affect the feasibility of the solution more than the grade.

Efficient air supply outlet form : The end air supply outlet in the centralized air supply system can be equipped with HEPA/ULPA air filter , selected according to the air volume of the workstation.

Regardless of the form, sealing and leak detection must be in place. The value of local air supply is to accurately deliver clean air to the protected area. If the interface leaks and unfiltered air is mixed in, no matter how high the level is, it will be compromised.

What to check when upgrading or remodeling

If the original plan was to use H14 and now you are considering upgrading to ULPA, there are a few things you need to confirm in advance.

Fan margin. The resistance of ULPA is usually higher than that of H14 of the same size, and the air volume may decrease after upgrading. It is necessary to take the resistance data of the new filter element at the target air volume and calculate the working point according to the fan curve.

Installation space. The thickness or structure of the new filter element may be different from the original product. It is necessary to confirm whether it can be installed into the existing box, whether the access door can be closed, and whether the replacement path is smooth.

Sealed interface. The matching dimensions of the gasket or liquid tank must be checked item by item, not just the appearance. For issues involving the sealing structure, please refer to the relevant interface verification methods.

Leak detection methods. The judgment limits of U15 and U16 are stricter than H14. The measuring range and scanning method of on-site leak detection instruments must be able to meet the requirements of the new level.

The verification process cannot be omitted. After the upgrade, it is necessary to re-measure the air volume, perform leak detection, and confirm the particle concentration in the protected area according to project requirements. The operating data before the upgrade should be retained as a comparison baseline.

Project judgment example

The overall clean room of a certain sensor packaging line is Class 1,000, but defective particles occasionally occur at the optical window mounting station.

The investigation found that the workstation was located inside the equipment, with a mechanical arm moving above it, and the airflow in the overall clean room could not effectively cover it. The original plan only opened an air outlet on the equipment casing without independent filtration.

The solution in this case is not to upgrade the entire clean room, but to add a local air supply unit to the work station. Depending on the particle sensitivity, you can choose H14 or U15 filter elements, and design the air duct and return air path according to the internal structure of the equipment. The installation method must be confirmed together with the moving parts of the equipment and maintenance access. Specific configuration can be combined Discussion on the structural scheme of the fan filter unit at the EFU equipment end .

Selection and Acceptance Checklist

About Aili Industrial’s packaging clean package

When it comes to clean solutions for precision electronics and sensor packaging, the difficulty often lies not in a single product, but in the coordination of the workstation structure, airflow path and filtration level.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide HEPA/ULPA products of different grades and supporting air supply equipment. Filter can be used with FFU fan filter unit、The EFU equipment-end fan filter unit checks the air volume, resistance and installation interface together to reduce the air volume mismatch or inability to install after the work station is modified.

When enquiring, provide the workstation structure, particle control targets, available space and acceptance methods, which will help determine the combination of filtration level and air supply form. Specific performance is subject to product technical data and project acceptance results.