Existing Cutting Technologies
For years now, there have been two major glass-cutting methods: Mechanical Scribing or Sawing and Laser Cutting
The explosive rise of high-tech manufacturing has put new demands on these existing cutting technologies.
Mechanical scribing and breaking is the classic and most prevalent glass separation technology. This is a process that involves the mechanical scribing of a vent in the upper surface of the glass. This is usually accomplished with a diamond or tungsten carbide wheel. The result of this is a score line. What which is a combination of controlled damage to the surface, lateral cracks, and when the parameters are well controlled, a vent crack is created. Mechanical scribing and breaking perform in a reasonably well-controlled manner when the operational parameters are correctly optimized. High performance scribing requires optimization to minimize the damage to the glass surface while maintaining a vent crack that is sufficient for a good break. Unfortunately, maintaining control of operational parameters is often somewhat of an art, not well understood by process engineers, and causes yield loss at many FPD companies. In Fig.1: Laser Cutting & Mechanical Scribe mechanical scribing, the vent is created in only the top 10 - 20 percent of the glass thickness. Applying pressure on the opposite side of the glass mechanically breaks the glass. This is generally done through an impact, roller or guillotine breaker.
2. Problems with Current Technologies
The major limitations of this technology are:
• Particulates are generated during the scribing process along with surface damage and lateral cracks. These imperfections generated during the scribing process often fracture later resulting in latent product failures (often as a result of shock).
• The scribe tool rolling or sliding over the glass surface may also generate particulates during the scribing process. In many applications this may not be an issue, however, when FPDs are scribed prior to assembly, the generated particulates are extremely damaging and must be completely removed.
• After-break edge quality and yield are greatly dependent upon the skill and knowledge of the process engineer.
• Yield loss occurs during the break process.
• After assembly, one additional limitation is that the edge quality does not meet all customer specifications and requires additional processing, such as edge seaming. The equipment required for this process is expensive and adds additional processing steps.
3. ZWLCT® Details
Our latest mathematical modeling and empirical data gathering resulted in the development of an improved METHOD and the requisite industrial machinery to enable us to introduce these improvements into the FPD industry. With this new METHOD we can create internal tensile forces so great that we can achieve total separation of display type glasses WITHOUT COOLING. Under these conditions the MicroCrack™ would propagate in the glass body at a depth of more than 1.1 mm (for bare glass). This process is called Full Body Separation.
Fonon Technology International has developed a completely new industrial method known to the world as Zero Width Laser Cutting Technology® - ZWLCT®.
The ZWLCT® METHOD splits materials on the molecular level with tremendous speed, no material loss, and no chips or other debris associated with conventional Scribe and Break technology.
The process depends upon the preheating of the material to be cut with an incident beam of radiation which heats the material just short of its softening point. One region of the heated zone is locally cooled to form a blind crack in the material. This crack is well controlled and can be modified in the depth, shape and angle of the cut face formed by the crack by changing the laser power and geometry. correct power density profile. This creates the intermolecular separation of the glass substrate to a certain depth, t.
Zero Width Laser Cutting Technology® produces the maximum MicroCrack depth still using controlled propagation of the MicroCrack in the subsurface layer of the glass and not thermal-fracturing of the glass.
The ZWLCT® METHOD incorporates cooling of the glass surface following controlled heating, with the correct power density profile, this creates the intermolecular separation of the glass substrate to a certain depth, t. Depth t has an inverse relation to the speed ( v ) of cutting, assuming that power ( P ) is constant. This means that the slower the speed the deeper the MicroCrack that is formed will be. Both mathematical models and empirical data support these conclusions and field experience has verified these findings.
The METHOD is for splitting materials by controlled propagation of a MicroCrack™ through the subsurface layer of glass (or other material) at an angle to the surface of the material. Laser energy is used because it is the most cost effective way of controlling the power parameters of an energy source. The scribe line is formed in such a way that no molecules leave the surface of the glass. The key is to achieve the right energy distribution within the beam. The specifics of this distribution depend on the physical properties of the glass (glass type).
The METHOD requires the initiation of a cut from the edge. For the FPD industry a laser based “Laser Cut Initiation Tool™ (LCIT)” is used which results in no chips or particles being generated by the initiation process.
Fonon has also modified its ZWLCT® METHOD by controlling the orientation of the tensile forces, developed within the glass body, to change the form of the Micro-Crack, resulting in the development of an Edge Chamfering METHOD and a Grooving METHOD for the
PDP industry, also utilizing Zero Width Laser Cutting Technology®. The edge is sealed as an inherent part of the process and as such retains the physical properties of the monolithic material.
Proven advantages of the ZWLCT METHOD include:
a. High scribing speed - up to 1000 mm/s
b. Extremely high accuracy- up to 10 microns achievable
c. Unlimited component size
d. No treatment of edges after processing
e. Easily integrated into any conventional process
f. Easily changed glass-processing thickness
g. Increased glass strength
h. Excellent surface integrity of cut surface
i. Precise edge geometry
j. Edge strength comparable with original material
k. Cut edge totally free of stress. This is extremely important for some applications and usually requires an additional process
• Economical advantages
a. No grinding and cleaning line necessary
b. Reduced space for laser scribing
c. The panel is three to five times mechanically stronger without additional edge processing
d. The same price or even less than precision mechanical scribers
e. Modular design utilizes standard components for easier service
b. Non-metallic brittle materials (i.e. Silicon, glass, wood)
There are many process variables which can cause problems if they are not addressed properly in an FPD process line. Some of these factors are: substrate coatings, coating of the edges, cutting surface coating over-spray, throughput and QC requirements, edge conditions, surface hardness, viscosity of the mnemonic fluid, glue dispensing defects, closeness to glue lines, reflective coatings on the cutting surface, substrate handling methods (they can change the thermal properties of a display substrate) and so on. In other words, because of the range of variables involved in the FPD process, optimal industrial performance can be achieved only by designing the process parameters for a particular product with its specific process requirements.
• Precision Scribing of Micro displays
A new generation of Micro-Displays require the new ZWLCT® METHOD of precise separation of glass substrates into individual displays without generating any debris on the glass surface. Because individual devices are very small (in average 15 x 15 mm), they were fixed on a special type of Quick Release film.
Full separation with a very high quality corners was achieved at a speed 600 mm/sec.
Special type of Quick Release film made it possible to remove individual displays from the cutting table without the edge damage. This unique method allows components to be cut with a precision of +/- 15 microns in cross-section in clean room environments.
• Biometric ID Devices separating method
With exposure in Biometric ID devices it became necessary to find a method of precision separation of glass panels into individual components without generating any debris on the glass surface. Bearing in mind that individual devices are relatively small (in average 25 x 25 mm), the handling is becoming an issue. ZWLCT® was applied to separate 0.7 mm glass substrates mounted on the special type of Quick Release film.
• Video Camera windows
Precision separation of glass substrates into individual camera windows with dimensions 9 x 10 mm in average is achieved by using Zero Width Laser Cutting Technology®. The process does not generate any debris on the surface, provides extremely high quality edges and scribe lines crossing on a micron level. The Method was applied to separate 150 x 150 x 0, 55 mm glass substrates.
• Cellular Phone TFT, Color STN, OLED cells separation
• Precision fabrication of Glass
Precision fabrication of glass wafers is possible using ZWLCT® as a disc scribing configuration of a compatible laser system. It produces a smooth, stress free, flawless edge without any material loss, edge chipping and without any further edge treatment.
• LCD - Production, Solar- cells and Photo masks
LCD production based on this new technology is dramatically improved in terms of both speed and quality. Cutting speeds of one meter/second are normal and the cutting is totally clean. Result: Undamaged surfaces and high strength, stress free edges to virtually any shape.
• Wafer dicing
For dicing wafers, ZWLCT® cuts in with zero width, greatly reducing wafer debris contamination and leading to less process damage.
Zero Width Laser Cutting Technology® can be used for precise glass separation at production speeds and forms not previously possible and with edge characteristics not attainable by any other process to date. When used in conjunction with our technology in the fields of surface processing and laser welding, exciting new possibilities for the design and production of components is realized.