July 2017 Archives

General description

Failure of thickness of any printed layers of glass substrates in the printing process can be caused by non-uniform heat treatment after printing. It may be attributable to handling of glass substrates during the transfer. This session explains available solutions to the problem.

Explanation

For glass substrates, silicon substrates, and other thin works, printing using resist solutions and other various dilute solutions should be processed in the continuous production line. Then, the printing process should be followed by preliminary drying and final drying heat treatment. Depending on whether or not the thin sheet-like works are handled appropriately in the heat treatment process, printing failure can occur. This session explains how the thin sheet-like works should be handled in the transfer line to prevent possible defective print quality after heat treatment due to any inconsistent heat conduction.

(1)Explanation about production line

-Glass substrates, silicon substrates, and other thin sheet-like works should be subject to cleaning, drying, printing, preliminary drying, final printing, and other processes continuously at specific durations of tact time in the automated resist processing line and drying line.
-Thin sheet-like works loaded in the production line, especially in the case where thin sheet-like works of different thicknesses are loaded, are likely to cause uneven thickness of printed layers in the heat treatment process.

(2)Explanation about possible causes for failure thickness of printed layers

-The printing process to glass substrates involves lifting up operation of the glass substrates by metal pins for handling on the tables for both printing machine and preliminary drying.
-When glass substrates are lifted up by metal pins on the preliminary drying table, failure thickness of printed layers occurs easily around the metal pins (Fig.1).
-This failure results from incomplete preliminary drying after printing, which is explained by the fact that due to the contact of metal pins with glass substrates, the contact area of heated glass substrates with metal pins becomes locally cooled, thereby leading to lowered temperature.
-Thus, the smaller the thickness of glass substrates and silicon substrates, the more severe failure thickness of printed layer occurs around the contact area with metal pins.

(3)Solutions to possible failure thickness of printed layers

-Due to the high thermal conductivity feature, metallic parts incorporate more thermal energy from glass substrates.
-In order to minimize the incorporation of thermal energy from metal pins, such solutions are recommended that adopt the design to apply a material of lower thermal conductivity for the tips of metal pins and/or change the material of the tips of metal pins (Fig.2).

General description

Unstable transfer can also occur due to many other causes in addition to those related to roller assembly.

Therefore, solutions must relate to the both aspects of structural design and practical use, including the mechanical design to realize stabilized and easily adjustable path lines of transfer systems and also the optimization of transfer speeds.

Explanation

This session explains the mechanical structure for the components other than the roller transport assembly. As a summary, the points of vital importance are listed for mechanical design of transfer systems to fulfill the requirements for glass substrates of reduced thickness and weight.

In the production line, the friction between the feed rollers and the substrates being transported varies due to a variety of factors related to the mechanical components other than the feed rollers.

Typical cases are listed below.

1. The transfer path line becomes deviated due to the vibration of equipment installed adjacent to the path line.
2. The heights of floors on which the transfer units are installed vary and therefore the reference height between the transfer units becomes different, resulting in a deviated path line.
3. The equipment layout is changed frequently and the transfer units have their path line adjustment capability designed not carefully, thus taking a huge amount of time for the adjustment. In addition, transfer trouble in the early stage of operation is unavoidable.

Table 1 summarizes typical problems involved in the thickness and weight reduction and their recommended solutions for the transfer systems.

[Table 1] Typical problems involved in substrates of reduced thickness and weight and their recommended solutions

Based on the above understanding, the important considerations for designing of appropriate transfer systems for glass substrates of reduced thickness and weight are listed below.

General description

The planned arrangement of feed rollers and the optimal allocation of friction coefficient of individual rollers allow prevention of possible meandering flow of substrates and improvement of motion control for straight transport.

Explanation

Explanation in this session focuses on the structural design to ensure transfer in a consistent straight line using the 3-rows independent feed roller system.

1)The number of rollers arranged and the planned arrangement

・ Increased stability of substrate transfer can be attained by making proper provisions to ensure well-balanced allocation of frictional force acting on individual rollers arranged to support each substrate.

2) Optimal allocation of friction coefficient of individual rollers to support each substrate

・ To ensure straight transport of loads being transported on the transfer line, the direction of action of frictional force for transport must be made straight.
・ For this purpose, optimal allocation of frictional force acting on individual rollers should be considered based on the concept of making the direction of action of frictional force easy to become straight even if the substrate support positions vary, by controlling the friction coefficient at each substrate support point of a roller.
・ The feed rollers equipped with rubber-made O-rings for transmission of frictional force and the auxiliary feed rollers made from plastic of smaller friction coefficient for auxiliary support of substrates are arranged alternately. This supports a flat plate at a total of 9 points, and at 5 or 4 of the 9 points, frictional force is transmitted, thus ensuring stable transfer.
・ The plan of arrangement of rollers with O-rings (Fig.1-Pattern A) provides agreement with the points for measurement of thickness of flat plates, showing a fundamental pattern for flat plate support.
・ The relation between substrates and roller positions in Pattern B, different from Pattern A, in which substrates move on the transfer line, is shown (in Fig.1-Pattern B).
・ Combined adoption of two roller arrangement patterns, A and B, facilitates linear movement of each substrate under well-balanced distribution of frictional force.

General description

Even in the case where the 3 rows independent feed roller arrangement is adopted, there can occur a problem of curved transport of glass substrates if any proper provisions to equalize the frictional force at all contact points between substrates and rollers are not provided.

Explanation

In Vol. 295, it was explained that 3 rows independent feed roller arrangement would be more favorable for transfer of thin substrates.This session explains the direction of transfer of substrates in this structural design.

1) The number of rollers arranged

・ In order to eliminate possible effects of unstable force for transport due to any deflected substrates, consideration may be given to increased number of substrate support points, thereby ensuring stabilized loading and frictional force at each point of contact with a roller.
・ In practice, however, the above-described solution alone cannot necessarily equalize the frictional force at all points of contact with the backs of substrates.

2) Stabilized transfer of glass substrates

・ To guide the loads being transported to move straight on the transfer line, the direction of action of frictional force for transport must be made straight.
・ There is no correlation between increasing the number of roller support points for substrates and making the direction of action of frictional force for transport straight.
・ If the frictional force acting on the feed rollers becomes unbalanced, the loads being transported fail to move straight but their transport direction changes, resulting in transport problems.
・ Fig.1 illustrates possible behavior of substrates being transported when the frictional force acting on the feed rollers differs between roller positions, or in this Figure, the frictional force is largest at the leftmost position followed by the middle and rightmost positions.Possible reasons why the frictional force becomes different include 1. bent shaft connecting the feed rollers, 2. partially or unevenly worn feed rollers, and 3. inclined horizontal reference for the transfer machines.
・ Therefore, in addition to the adoption of the 3 rows independent feed roller arrangement, proper provisions must be made to equalize the frictional force on the feed rollers supporting the substrates.