Silica Glass - Production Process

Typical process until precision product is completed.

Note) Since silica glass might be damaged due to a processing distortion, thermal treatment called “annealing” which removes the distortion between the processes is required, but in here such process is left out.

  1. Selection of Material
  2. Cutting/Slicing
  3. Grinding/Machining
  4. Polishing
  5. Channeling/Grooving
  6. Assembly
  7. Cleaning/Inspection
  8. Product

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This is the process for fabricating materials of products and for making the shapes of products. In Tosoh, we have our own precision grinding technology such as small-diameter drilling using machining center and laser beam machine, and build up our products by selecting and combining the most suitable processing method and processing machinery corresponding to required accuracy and quality.

As for the cells for use with flow cytometry (flow cells for use with blood/urine diagnosis equipment) which is our major business line, we are now mass producing such cells by using a special image-processing grinding system.

Comparison of Small Hole Drilling Methods
Method Minimum Size Accuracy Notes
Machining Center φ0.3 mm 0.02 mm
Laser Beam Machine φ0.3 mm 0.05 mm Developing φ0.01 mm
Ultrasonic Machine φ0.5 mm 0.05 mm
Typical values. Product specifications can be arranged according to proposals.

Tosoh uses various kinds of polishing machines, such as double-sided polishing machines which are suitable for substrate polishing, and one-sided polishing machines which are suitable for polishing structures and small-quantity production. This depends on the sizes of products and required specifications.

As for the flow cells installed in diagnosis/analytical equipment where improvement of high precision and spatial resolution is advancing, the defect standard with respect to the light transmission side is getting more and more strict year by year, polished surface without defects and is yet very flat is becoming a requirement. And, it is also imperative to improve the polishing technology from the viewpoint of improving the connecting quality. At Tosoh, we are always working on improving the polishing technology, including but not limited to enhancing the acquisition of qualification of nationally certified abrasion technicians.

Comparison of Polishing Methods
Method Maximum Work Size Polishing Medium (Final) Surface Roughness: Ra
Small Single-sided Polish φ200 mm Cerium Oxide 0.1 nm
Large Single-sided Polish φ1,000 mm Cerium Oxide 0.1 nm
Double-sided Polish φ400 mm Cerium Oxide 0.05 nm
Colloidal Silica 0.02 nm
Typical values. Product specifications can be arranged according to proposals.

Typically in optical flow cells and the like, flow passage (channel) is formed by fusing polished parts to each other. This method is effective for forming linear flow passage, but is not good enough for realizing a complex flow passage construction. Tosoh is realizing such products as having minute and complex flow pass construction such as microfluidic chip by using lithography technology as well as etching technology which are similar process used in the manufacture of semiconductor device.

In addition to above, channel/groove forming using such grinders as machining center and dicing saw etc. is also available for supply.

Comparison of Channeling/Grooving Methods
Method Channel Width Surface Roughness: Ra Available Pattern
Thermal Fusion ≥ 0.05 mm 0.0001 µm Straight
Lithograph & Etching ≥ 0.002 mm 0.002 µm Flexible
Machining Center ≥ 0.1 mm 0.2 µm Flexible
Dicing Saw ≥ 0.1 mm 0.2 µm Straight
Typical values. Product specifications can be arranged according to proposals.

It is possible that complex shapes are formed by assembling multiple parts in silica glass. Since the parts are completely integrated by such assembly, such products have been built up in such a way as to have almost the same characteristics as those of silica glass materials themselves. There are several preconditions for assembling by silica glass, including but not limited to the requirement that high temperature processing at over 1,000 degrees Celsius is necessary, and the requirement that contact area to some extent is necessary. And, in case when there is any difficulty in performing such assembly it is possible to assemble the materials by using certain type of glass frit or adhesive. Tosoh Quartz is now manufacturing in such way as selecting the optimum assembling method, taking into account quality and accuracy required for the products.

Comparison of Assembling Methods
Method Surface Distortion Heat-resistance Chemical Inertness
Furnace Fusing Excellent Excellent Excellent
Flame Fusing Good Excellent Excellent
Contact with Glass Frit Excellent Good Good
Contact with Adhesive Excellent Good Good
Typical values. Product specifications can be arranged according to proposals.

Products are cleaned in clean-room by utilizing the precision cleaning technology of semiconductor photomask level. And, the cleanliness of parts is also important for the purpose of improving products quality.

We use special cleaning machine originally designed and developed by ourselves to clean the cells for use with flow cytometry which is our major product, and have achieved the stabilized cleanliness by automatically cleaning the inside of channel (with the size of 200 to 250 micron). Products that have been cleaned are inspected in a clean-room. Visual inspection, supported by use of microscope, is conducted by experienced inspectors.

Any measurement of dimensions and geometrical tolerance is conducted by respective automatic measuring devices, and any and all measured values are utilized for quality control after compiling them into a database.