Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-07-22
2001-02-06
Le, N. (Department: 3861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S241000, C347S134000
Reexamination Certificate
active
06184917
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a laser marking method and apparatus which scans a liquid crystal mask having thereon a desired pattern to be marked by a laser beam to mark an object such as IC with the pattern by the laser beam passed through the liquid crystal mask, and particularly to improvement for improving a speed of response of the liquid crystal mask.
BACKGROUND ART
A laser marker is attracting attention as a technology for stamping marks such as a product serial number and an identification sign on a produced semiconductor device in a semiconductor device production process.
Such a laser maker scans a liquid crystal mask having thereon a desired pattern to be marked by a laser beam to mark the pattern on an object such as IC by the laser beam passed through the liquid crystal mask.
Conventionally, when the liquid crystal mask is driven, the ambient temperature at which the liquid crystal is operated is set to about the room temperature in consideration of the temperature characteristic of liquid crystal itself of a liquid crystal mask circuit board and the temperature characteristic of peripheral circuits on the circuit board.
Thus, the conventional technology drives the liquid crystal mask in an operation temperature range of about the room temperature, so that the liquid crystal element has a slow speed of response. Therefore, it takes time to change the patterns to be marked, and a working efficiency of laser marking is not improved satisfactorily. In other words, when the liquid crystal element is driven in the operation temperature range of about the room temperature, a viscosity of the liquid crystal element is increased as compared with its driving at a high temperature, resulting in lowering the speed of response.
Recently, there have been proposed the liquid crystal element and peripheral circuits having good heat-resisting properties, and the environment, where the operation temperature range of the liquid crystal mask can be increased to the room temperature or above without any problem, is being prepared.
FIG. 8
shows a relation between liquid crystal drive voltage V and transmissivity of liquid crystal at five different temperatures. Conventionally, when the liquid crystal mask is driven, the liquid crystal drive voltage (ON voltage) V is set to voltage value Va of a range that the transmissivity of liquid crystal is largely changed in correspondence with a change in liquid crystal temperature. Therefore, the conventional technology adjusts to increase or decrease the drive voltage V depending on the temperature change in order to keep the transmissivity of liquid crystal as constant as possible.
But, the conventional technology cannot be used under a situation that the temperature change is extreme and its control to keep the transmissivity of liquid crystal at a fixed level is limited. And, the conventional technology needs an additional circuit for controlling to keep the transmissivity at a fixed level. Thus, it is disadvantageous in view of a cost and a space.
The present invention was achieved in view of the circumstances described above. And it is an object of the invention to provide a method and apparatus for laser marking which have improved efficiency of laser marking work by improving a response speed of liquid crystal and can perform the laser marking operation without being influenced by a change in external environmental temperature.
It is also an object of the invention to provide a method for driving a liquid crystal element, which can keep a constant transmissivity even under a condition with an extreme change in temperature.
DISCLOSURE OF THE INVENTION
The present invention relates to a laser marking apparatus in which a liquid crystal mask having thereon a desired pattern to be marked is scanned with a laser beam to mark on an object with the pattern by the laser beam having passed through the liquid crystal mask, characterized in that the apparatus comprises: temperature control means for maintaining the liquid crystal mask in a predetermined high-temperature condition higher than a room temperature; and control means for controlling to perform the marking operation by the laser beam in the high-temperature condition.
According to the invention, the laser marking operation is performed with the liquid crystal mask maintained in the predetermined high-temperature condition higher than the room temperature, so that the response speed of the liquid crystal is improved. Thus, time for switching the marking patterns can be shortened, and the laser marking working efficiency can be improved. Since the liquid crystal mask is maintained in the high-temperature condition substantially higher than the room temperature, the laser marking work can be performed without being influenced by a change in external environmental temperature (room temperature). Thus, the transmissivity of liquid crystal is not largely affected adversely even when the liquid crystal drive voltage is set to a voltage which is influenced by a change in temperature.
The invention uses the laser beam, which is essential for the laser marker, as heat source for maintaining the liquid crystal in the high-temperature condition.
Accordingly, the invention does not require another heat source for increasing the liquid crystal temperature. Thus, energy can be used effectively, and a cost and a space can be saved. Since the laser beam having good heat concentration is used, it serves to increase only the temperature of the display area of the liquid crystal mask, and an influence of heat to the peripheral parts can be decreased.
The invention sets the drive voltage to be in a range that the ON transmissivity is hardly changed even if the liquid crystal temperature is changed and drives the liquid crystal element by applying the determined drive voltage.
Therefore, the invention minimizes the change in transmissivity of liquid crystal even when the temperature of the liquid crystal is changed or the peripheral environmental temperature is changed, and the stamp quality can be kept uniform even if the environmental temperature is changed extremely.
REFERENCES:
patent: 5734145 (1998-03-01), Ichihara et al.
patent: 5942136 (1999-08-01), Mori et al.
patent: 2-293820 (1990-12-01), None
patent: 3-116016 (1991-05-01), None
patent: 5-42761 (1993-02-01), None
patent: 6-226476 (1994-08-01), None
patent: 6-304775 (1994-11-01), None
International Search Report in PCT/JP97/04337, Feb. 24, 1998.
Chiba Teiichiro
Okubo Tsuyoshi
Sugimoto Yukihiko
Komatsu Ltd.
Le N.
Nguyen Lamson D.
Varndell & Varndell PLLC
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