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POREX® Tubular Membrane Filter (TMF)™ Applied in Backgrinding and Die Sawing Wastewater Reclaim System for an Integrated Circuit Packaging Plant in Suzhou, China.

Circuit Packaging Plant

Backgrinding and die sawing are two steps in the Integrated Circuit (IC) packaging process. For easier transportation and protection of the wafer, the thickness of the industrially produced wafer is larger than required. Therefore, before the IC is packaged, it is ground to a thin disc in the “backgrinding process”. Die sawing is another process which is used to cut large silica wafers into smaller discs (see diagram below). After either of these processes, the wafer chips must be rinsed with Ultrapure Water (UPW) to remove fine silica particles and any other contaminants. Backgrinding wastewater and die sawing wastewater are typically discharged from the IC packaging plant. This discharged water normally contains only UPW and fine silica particles, but on occasion some grinding fluid is also present. Removal of the fine particles from the wastewater is critical to allow recycle and reuse of this large volume of water.

This document will review a working reclaim system for backgrinding and die sawing wastewater using POREX® Tubular Membrane Filter (TMF)™ system. Facilities using this process find it to be an excellent option for this application.

Grinding Wheel Image

Wastewater Information

In this facility, there are two streams of wastewater being treated by Porex TMF:

  • Wastewater from the site’s workshop (backgrinding and die sawing) totaling 100 m3/day.
  • Backwash wastewater from the site’s existing hollow fiber ultrafiltration (UF) membrane system. The hollow fiber UF system was commissioned in 2010, also for backgrinding and die saw wastewater treatment. The UF permeate water is sent back to the facility’s UPW treatment system. During service, the the hollow fiber UF system is backwashed every 30 minutes. About 60~70 m3/day of wastewater are discharged to the Porex TMF system.

The total Porex TMF system is designed to handle 200m3/day, or approximately 12 m3/hr. The mixed raw wastewater is brown in appearance with numerous very fine particles in the liquid. These particles are very hard to precipitate naturally; a container of the water sample was set out for gravity settling for over one month and no solid/liquid interface could be found.

TMF Characteristics and Advantages

When used to treat backgrinding and die sawing wastewater the advantages of Porex TMF process are:

  1. Combined with a filter press, this system will divide the wastewater into two parts: filtered water and dewatered sludge cake. There is no concentrated or reject water drain resulting in a nearly 100% recovery rate.
  2. No chemical dosing into the wastewater is necessary. Therefore, if desired, sludge can be reclaimed for future reuse.
  3. No pretreatment stage; the entire system uses simple physical solid/liquid separation.
  4. The proprietary POREX® Tubular Membrane Filter (TMF)™ has very high abrasion resistance.
  5. The membrane layer is not destroyed by acute silicon particles. Normally this is the biggest challenge when hollow fiber UF membrane technology is utilized for this kind of water. Hollow fiber plugging or breakage can occur due to the small particles size, high concentration and very abrasive nature of the particles.
  6. Maintenance of the system is simple. The system can be designed for automatic operation, and can be placed into service mode from standby mode without any upsets or problems.
  7. The Porex TMF membrane has good resistance to fouling compared with hollow fiber membranes and flux is more easily recovered after chemical cleaning.
  8. The system design allows for a skid fame requiring less space than other methods.
  9. Expansion capability; water capacity can be enlarged by simply adding more skids or modules.

Porex TMF System Information

The details below describe the installed Porex TMF system.

Water capacity: 200 m3/day, divided into 2 trains.
Module Specification: Porex TMF system (module model # MME3005613VP)
Tubes per Module: 13
Module Housing: PVC housing
Membrane tube diameter: 1 inch
Membrane: 0.05 micron
Active membrane surface area: 1.82mper module.
Module quantity: 12 modules per train, 2 trains per unit, totaling 24 modules in this system.

Process Schematic

 TMF Process Schematic

Process Description

The system was implemented in November 2011 and system performance has met or exceeded the design specification. The initial filtrate water flow rate is higher than 16 m3/hr. Filtrate water turbidity is less than 1 NTU and filtrated water conductivity is less than 20 μs/cm.

Operation Status

The system was implemented in November 2011 and system performance has met or exceeded the design specification. The initial filtrate water flow rate is higher than 16 m3/hr. Filtrate water turbidity is less than 1 NTU and filtrated water conductivity is less than 20 μs/cm.

Suzhou Operation Status

The TMF system has no effect on product water conductivity. The low conductivity is due to the low TDS load in the influent water. Product water turbidity as shown in the above photo

Summary 

The Porex TMF system is widely used for backgrinding and die sawing wastewater. The excellent filtrate quality, high recovery rate, lack of needed chemical dosing, and ease of operation make the system superior to other processes and technologies in this application.

Click here to download the full Porex Filtration Suzhou Case Study 

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