KR20010038850A - Method of enhancing releasing effect of mold using low temperature plasma processes - Google Patents

Abstract

PURPOSE: A method for improving the releasing property of a mold using the low temperature plasma process is provided to obtain a method for coating on the mold a polymer thin film which not only is not contaminated by materials such as a releasing agent due to the excellent releasing property but also has the high durability due to the high cohesion to the mold. CONSTITUTION: In a method for improving the releasing property of a mold by coating a polymer thin film comprising pretreatment step of treating the mold with the reactive gas plasma; and plasma polymer coating step of depositing the polymer produced by plasma polymerizing a monomer gas on the mold (11), the polymer coating step comprises a binding layer (12) coating step of coating the pretreated mold by polymerizing as gradually increasing the pressure of a reaction chamber (the pressure of the monomer gas); and a functional layer (13) coating step of coating the binding layer coated mold by polymerizing as constantly maintaining the pressure of the reaction chamber.

Description

Improved mold release property using low temperature plasma process {METHOD OF ENHANCING RELEASING EFFECT OF MOLD USING LOW TEMPERATURE PLASMA PROCESSES}

The present invention relates to a method for securing mold release property between a mold and a plastic molding, and more particularly, to a method of securing durability with mold release property by coating a polymer thin film having high adhesion to a mold by a low temperature plasma process.

Many kinds of plastic products are molded using a mold. For example, the semiconductor packaging process will be described below.

The semiconductor encapsulation process includes a lead frame method, a pin grid array (PGA) method, a ball grid array (BGA) method, and the mold is used by either method, and is used as an encapsulant to secure mold release properties between the mold and the molded product after molding. The epoxy molding compound (EMC) to be contained contains a releasing agent.

However, the release agent allows the molded product to be easily separated from the mold after molding as desired, while remaining on the surface of the mold along with other low molecular materials constituting the EMC to carbonize or polymerize to contaminate the mold.

Therefore, defects occur in the molded article unless the mold is periodically cleaned or the mold is prevented from being inherently contaminated.

At present, the cleaning process to remove contaminants by periodically cleaning the mold is generally adopted. In the cleaning process, the melamine cleaning method which removes contaminants by molding the melamine resin for mold cleaning with the contaminated mold, and sand blast ( There is a method of mechanically removing contaminants by sand blast or copper knife, and chemically removing contaminants using strong alkali and emulsifier. Either method requires stopping work for cleaning. (2 hours per day) There is a disadvantage in that the productivity is lowered, and each cleaning compound is consumed separately (melamine cleaning method), dirt removal is incomplete or the mold may be damaged (mechanical method), or the device may be The disadvantage is that it is difficult to apply (chemical method) unless it is completely decomposed.

Thus, attempts were made to prevent contamination of the mold surface with residues such as mold release agents by increasing mold release properties. Korean Patent Application No. 97-58942 discloses that a surface of a mold is pretreated with a reactive gas plasma. A method of improving mold release property by plasma polymerizing gas and coating the surface of a mold with a polymer thin film is proposed.

However, by simply coating the plasma polymer on the mold, the releasability can be increased (critical surface tension: 23 to 30 m · N / m ² ), but the adhesion between the mold and the polymer thin film coated thereon is low and the polymer flows. The thin film is easily peeled off by internal stress.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of coating a polymer thin film having excellent durability and high adhesion to a mold without being contaminated by a release agent or the like.

1 shows a cross section of a thin film coated according to the invention.

2 illustrates one embodiment of a plasma reactor system used in the practice of the present invention.

** Explanation of symbols for main parts of drawings **

11: mold 12: bonding layer

13: functional layer 21: reaction chamber

22: (sample) mold 23: RF power supply

24: flow meter 25: valve

26: vacuum pump 27: throttle valve

28: gas

The present invention for achieving the above object, (A) a pretreatment step of treating the mold with a reactive gas plasma; (B) A method of coating a polymer thin film comprising a plasma polymer coating step of depositing a polymer produced by plasma polymerizing monomer gas on a mold to improve mold release property, wherein the polymer coating step (B) is performed by (b-1). Bonding layer coating step of polymerizing and coating while gradually increasing the pressure of the reaction chamber (pressure of the monomer gas); (b-2) It characterized in that the functional layer coating step of coating by polymerization while maintaining a constant pressure in the reaction chamber.

Referring again to the features of the present invention using FIG. 1, the present invention provides a step (B) of coating the plasma polymer on the mold by plasma polymerization by gradually increasing the pressure of the monomer gas (i.e., in an abnormal state) to bind the bonding layer. Coating (b-1); The mold 11 and the functional layer 13 having high releasability are carried out by dividing into a step (b-2) of coating the functional layer by plasma polymerization while maintaining the pressure of the monomer gas constant (that is, in a steady state). In order to have a bonding layer 12 whose properties change gradually.

The attempt of the present invention is easy because the polymer thin film of the plasma polymer-coated mold is easily peeled off by the conventional method. The assumption is that the bond strength is large, and the fact that the more severe the plasma polymerization conditions, the more inorganic silicon compounds and / or carbon compounds are produced, and the milder the polymerization conditions, the more organic polymers are produced. It comes from.

In the low temperature plasma polymerization process, W / FM [where W is the energy input (watt), and F and M are the molar flow rates and molecular weights of the polymerization gas flowing into the reaction chamber, respectively. Therefore, FM is mass flow rate and the unit of W / FM is Joule / Kg.] Is employed as the most important operating parameter that determines the physical properties of the plasma polymer to be polymerized. It is known that a large W / FM forms a silicon compound layer and / or a carbon compound layer close to an inorganic material, and a small W / FM polymerizes a polymer close to an organic material in which the molecular structure of the monomer gas is relatively well preserved.

However, in an abnormal state, since the pressure of the polymerization gas in the reaction chamber is continuously increased, W / FM is not meaningful, and the energy input amount per unit mass of the monomer gas in the reaction chamber is meaningful. In this case, however, the effective volume is difficult to determine properly since it depends on the size and shape of the reactor, the distance between the electrodes, and the like. Therefore, the energy input amount to the density of the monomer gas present in the reaction chamber at this point, that is, W / ρ, will be used as an operating variable instead of W / FM at the steady state. [Including ρ (density) in the operating variables, it is not necessary to include p (pressure) and M (molecular weight), and the unit of W / ρ is Joule / (Kg / m ³ ) · min.]

The coating of the bonding layer (b-1) is carried out by gradually increasing the pressure of the reactive gas from 0.1 to 10.0 milli torr to 10 to 50 milli torr, with a W / ρ of 10 to 200 mega Joule / (Kg / m ³ ). Terminate in the range of min. [In this case, when hexamethylenedisiloxane (HMDSO) is used as the reactive gas, the initial value of W / ρ becomes 1,300 to 13,000 mega Joule / (Kg / m ³ ) · min.] Here, W / ρ The value can be adjusted by changing the energy input per unit time, that is, W, in addition to the pressure of the reactive gas. In this way, the coated bonding layer has a characteristic of gradually changing from inorganic to organic as it moves away from the interface with the mold.

In addition, the coating of the bonding layer (b-1) may be carried out continuously. This allows quick access to the properties of the functional layer without making the thickness of the bonding layer too thick without significantly impairing the bonding force in the bonding layer. If the thickness of the coating layer is a thin film is likely to peel off. For example, 1 minute (on) → 2 minutes (off) → 2 minutes (on) → 3 minutes (off) →. Can be supplied by

The coating of the functional layer (b-2) is carried out at a steady state with a pressure of the reactive gas of 10 to 100 milli torr so that the value of W / FM is 100 to 2,000 mega Joule / Kg. The value of W / FM can be adjusted by changing the energy input per unit time, ie, the value of W, in addition to the pressure of the reactive gas as in the coating of the bonding layer.

In addition, the coating of the functional layer (b-2) may be carried out in a steady state of 2 to 3 steps while lowering the value of W / FM. This can be achieved by increasing the pressure of the monomer gas step by step or by lowering the energy input per unit time.

It is preferable that the thickness of the coating layer not exceed 2.0 μm by adding the thicknesses of the bonding layer and the functional layer. If the thickness of the coating layer is too thick, it is easy to peel off, and if it is thin, it cannot be used for a long time.

As the monomer gas, an organosilane is used. Preferably, methylsilane, ethylsilane, dimethylsilane (DMS), trimethylsilane (TMS), tetramethylsilane, trimethylethoxysilane, methyltriethoxysilane, hexamethyldisiloxane (HMDSO ), Tetramethyldisilazane, hexamethyldisilane, or tetramethyldisiloxane.

Plasma pretreatment (A) is carried out by known methods and uses oxygen or air plasma. In particular, it is known that oxygen plasma effectively removes organic contaminants on the surface of the mold and has high etching effect to increase adhesion to the plasma polymer deposited.

In addition, when the coating of the functional layer is completed, a step of heat treatment by a known method may be added. For example, heat treatment is performed by leaving it in a reaction chamber at a pressure of 1.0 milli torr or less and a temperature of room temperature to 250 ° C. for 1 to 2 hours. It is known that the heat treatment eliminates free radicals in the coating layer, so that there is little change over time in physical properties such as contact angle.

The construction of the present invention will become more apparent in the examples.

<Example 1>

Plasma pretreatment and plasma polymer coating were carried out using the system shown in FIG. 2, and the reactor 21 had a volume of 150 lit. In FIG. 2, although the sample mold 22 is shown floating in the space of the reactor, the mold itself may be used as an electrode, or another type of power source may be used instead of the RF power source 23. Those skilled in the art will appreciate that other configurations can be made. The pressure of the reactor is regulated through a throttle valve 27 connected to the vacuum pump 26 at the same time as it is regulated through the valve 25 of the flow meter 24.

As a sample mold, a chromium (Cr) plated mold for semiconductor encapsulation (BGA method) was used, and hexamethyldisiloxane was used as a monomer gas.

Specific coating conditions are as follows.

(1) Plasma pretreatment: After washing the mold with water and drying, the pressure of the reaction chamber is 50 milli torr and the energy input amount per unit mass (W / FM) is 1.4 giga Joule / Kg (W = 100 watt). Pretreated for 15 minutes.

(2) Coating of the bonding layer: The hexamethyldisiloxane pressure was gradually increased from 1 milli torr to 20 milli torr with an energy input (W) of 210 watts. At the end, W / ρ was 65.5 mega Joule / (Kg / m ³ ) · min, and the thickness of the thin film was 0.5 μm.

(3) Coating of functional layer: The hexamethyldisiloxane was coated in two stages at a pressure of 20 milli torr and a flow rate of 2.6 ml / min. First, the energy input (W) was 190 watts (W / FM = 599.6 mega Joule / Kg), and second, the energy input was 90 watt (W / FM = 284.0 mega Joule / Kg). The thickness of the coating in each step was 0.5 μm each.

Through the above process, the coated mold was measured with 95 ° contact angle to pure water and 22N · m / m ² of critical surface tension (average value measured 5 times). As a result of injection molding the product as EMC, it was possible to mold 30,000 times or more.

As a result of measuring the Mohs hardness of each thin film layer, the upper layer of the bonding layer was 2.7, the first thin film of the functional layer was 2.6, and the second thin film was 2.55.

<Example 2>

The same apparatus and sample (mold) as used in Example 1 were used, and tetramethyldisiloxane was used as the monomer gas.

Specific coating conditions are as follows.

(1) Plasma pretreatment: After washing the mold with water and drying, the pressure of the reaction chamber is 50 milli torr and the energy input amount per unit mass (W / FM) is 1.4 giga Joule / Kg (W = 100 watt). Pretreated for 15 minutes.

(2) Coating of bonding layer: Increase the pressure of tetramethyldisiloxane from 1 milli torr to 20 milli torr with the energy input amount (W) of 250 watts, coating for 2 minutes and resting for 2 minutes for a total of 10 minutes ( Coating time). At the end, W / ρ was 94.8 mega Joule / (Kg / m ³ ) · min, and the thickness of the thin film was 0.5 μm.

(3) Coating of functional layer: Coating was carried out in three steps with a pressure of tetramethyldisiloxane of 20 milli torr and a flow rate of 2.6 ml / min. The first has an energy input (W) of 190 watts (W / FM = 599.6 mega Joule / Kg), the second has an energy input of 140 watts (W / FM = 441.8 mega Joule / Kg), and the third The energy input was 90 watt (W / FM = 599.6 mega Joule / Kg). The thickness of the coating in each step was 0.3 μm each.

Through the above process, the coated mold was measured with 92 ° contact angle to pure water and 24N · m / m ² of critical surface tension. As a result, it was possible to mold 35,000 times without damaging the coating.

As a result of measuring the Mohs hardness of each thin film layer, the bonding layer was 2.7, the first thin film of the functional layer was 2.6, the second thin film was 2.55, and the third thin film was 2.55.

According to the present invention, the mold can be coated with a thin film having good releasability and durability, thus eliminating the need to use a cleaning agent, and reducing the work loss due to shut-down.

Claims (6)

(A) a pretreatment step of treating the mold with a reactive gas plasma; (B) A method of coating a polymer thin film comprising a plasma polymer coating step of depositing a polymer produced by plasma polymerizing monomer gas on a mold to improve mold release property, wherein the polymer coating step (B) is performed by (b-1). Bonding layer coating step of polymerizing and coating while gradually increasing the pressure of the reaction chamber (pressure of the monomer gas); (b-2) A method for coating a mold, comprising a functional layer coating step of coating by polymerization while maintaining a constant pressure in the reaction chamber. The method of claim 1, wherein the coating of the bonding layer (b-1) is achieved by gradually increasing the pressure of the reactive gas from 0.1 to 10.0 milli torr to 10 to 50 milli torr, and finally the value of W / p is 10 A coating method of a mold, characterized in that it terminates in the range of -200 mega Joule / (Kg / m ³ ) · min. The method of claim 1, wherein the coating of the bonding layer (b-1) is made intermittently while lowering the value of W / ρ. The method according to claim 1, wherein the coating of the functional layer (b-2) is made in a steady state in which the pressure of the reactive gas is 10-50 milli torr and the value of W / FM is 100-2,000 mega Joule / Kg. Coating method of mold. The method of claim 1, wherein the coating of the functional layer (b-2) is carried out at a steady state in two to three steps while lowering the value of W / FM. The monomer gas according to any one of claims 1 to 5, wherein the monomer gas is methylsilane, ethylsilane, dimethylsilane (DMS), trimethylsilane (TMS), tetramethylsilane, trimethylethoxysilane, methyltriethoxysilane, hexa A method of coating a mold, characterized by using an organosilane selected from methyldisiloxane (HMDSO), tetramethyldisilazane, hexamethyldisilane, or tetramethyldisiloxane.