KR100260232B1 - Polymer thin layer coating method of pcb for semiconductor packaging by the bga and the pcb manufactured thereby - Google Patents

Abstract

PURPOSE: A method for coating a polymer thin film on a surface of a PCB(Printed Circuit Board) used when packaging a semiconductor by a BGA(Ball Grid Array) method and a PCB thereof is provided to increase an adhesive strength in a coating process on a surface of a PCB by polymerizing a polymeric gas with a low temperature plasma. CONSTITUTION: A plasma polymer is generated by performing plasma polymerization for a polymeric gas. The plasma polymer as a thin film is coated on a surface of a PCB used when packaging a semiconductor by a BGA method. The plasma polymer is bonded to an EMC(Epoxy Molding Compound) used as a packaging agent for the PCB.

Description

Method of coating polymer thin film on the surface of PC used for semiconductor encapsulation (PAC) by BAA method and PC manufactured by

The present invention relates to a surface treatment method of a printed circuit board (PCB), and in particular, a PCB (printed circuit board) used when packaging a semiconductor by a BGA (Ball Grid Array) method and an EMC (used as an encapsulant). The present invention relates to a method of coating a plasma polymerized polymer thin film on a PCB surface to improve adhesion to an epoxy molding compound, and a PCB manufactured thereby.

Methods of encapsulating a semiconductor include a lead frame method, a pin grid array (PGA) method, and a ball grid array (BGA) method.

Among them, the BGA method is a method of attaching a processed wafer on a PCB, performing wire bonding, and then injection molding, wherein the adhesive force between the PCB surface and the EMC used as an encapsulant is used. Is required.

To improve the adhesion between the PCB and the EMC, there is a method of etching the surface of the PCB by plasma treatment and the method of enhancing the adhesion of the EMC itself.

Etching is usually performed using argon gas plasma, which is to roughen the surface of the PCB to widen the contact surface with EMC, increase the mechanical adhesion by the uneven surface, and increase the surface free energy. However, only etching the surface of the PCB does not significantly increase the adhesive force, and thus has a drawback in that the defect rate of the semiconductor chip manufactured is high.

In addition, the method of increasing the adhesive strength of the EMC itself has a drawback that the adhesive strength with the PCB during injection molding is also increased (ie, the mold release property is lowered), resulting in poor workability of the injection molding process and weak mechanical strength.

An object of the present invention is to coat a polymer thin film having good affinity with EMC by using a low temperature plasma polymerization process to improve the adhesion between the surface of the PCB used to encapsulate the semiconductor by the BGA method and the EMC used as the encapsulant. To provide a way.

Another object of the present invention is to provide a PCB with improved adhesion to the EMC produced by the above method.

1 is a schematic diagram of a low temperature plasma reactor using RF power

<Description of the symbols for the main parts of the drawings>

11 reaction chamber 12 sample

13: RF Power 14: Matching Network

15: stop valve 16: flow meter

17 gas container 18 vacuum measurement and control

19: throttle valve 20: vacuum pump

21 electrode 22 power supply time regulator

The present invention provides a method for producing a PCB having a surface having a good affinity with EMC, which is used as a semiconductor encapsulant, by coating a polymerized gas on the surface of a PCB by plasma polymerizing a polymerizable gas, in particular, an organic compound containing carbon, using a low temperature plasma process. It provides a PCB manufactured thereby.

A pretreatment process for treating the PCB surface with a plasma of inert gas or reactive gas before the coating process and a post treatment process for treating the PCB surface coated with plasma of inert gas or reactive gas after the coating process may be optionally added.

Low temperature plasma refers to a gas state that is partially ionized and wholly electrically neutral, and is easily obtained by electrical discharge in low pressure gas or vapor. Reactive Species, such as electrons, photons, ionized atoms and molecules, and free radicals, exist in low-temperature plasma, and low-temperature plasma is a process for modifying the solid surface using these reactive species. Or it can be divided into Plasma Treatment process that changes the physicochemical properties of molecules on the solid surface according to the type of vapor and Plasma Polymerization process where a polymer thin film is coated on the solid surface. Plasma treatment uses inert gases (e.g. helium, argon) and gases with simple structures (e.g. oxygen, hydrogen, nitrogen, carbon dioxide, water vapor, air, etc.), and polymerizable gases and vapors (e.g. (Eg, hydrocarbons, organic silicon, fluorocarbons, etc.) are used depending on the desired surface properties.

Plasma polymerized polymers penetrate into the interior of the subject (here PCB) during polymerization, resulting in atomic and admixture of the subject, resulting in stronger adhesion to the subject than any other polymer. In addition, free radicals are present on the surface of the polymer thin film, and when the EMC is formed, the free radicals are combined with the free radicals of the epoxy so that the bonding force is very high.

The present invention relates to a polymer produced by placing a PCB (e.g., a substrate made of glass fiber reinforced bismaleimide triazine) in a reaction chamber and glow discharged in a low pressure polymerizable gas, to the substrate surface accurately. It is made by deposition on the surface of the metal surface, the plated metal surface and the surface of the solder mask (Plasma Enhanced Chemical Vapor Deposition).

Before and after the coating process, a pretreatment step and a posttreatment step of treating with a plasma of inert gas or reactive gas may be added, respectively.

The coating process may be performed at any point before forming the PCB circuit in the semiconductor encapsulation process and before the EMC molding. Coating the IC die prior to bonding can also improve the adhesion between the die's epoxy bond and the PCB substrate.

If the coating is performed prior to wire bonding, it may be necessary to apply the coating while masking a portion of the PCB.

In addition, if coating is carried out after mounting the wafer, it may be necessary to mask the site such as the wafer and then apply the coating. As a masking method, there is a method of attaching a masking sheet directly to the surface of the subject, but preferably, the workability will be improved if the member is attached to the jig used when mounting the subject in the reactor. .

Hereinafter, a process for coating the plasma polymer on the surface of the PCB will be described in detail by function.

As described above, the plasma pretreatment step of the first step and the plasma post-treatment step of the third step may be omitted, respectively.

A schematic diagram of a system for plasma pretreatment is shown in FIG. 1, which is intended to illustrate the configuration of the invention and does not limit the scope of the invention. Those skilled in the art will be able to construct a variety of other systems for practicing the present invention.

In addition, the system of FIG. 1 is equally used not only in the pretreatment step but also in the plasma polymerization process and the post-treatment process of coating the plasma polymerized polymer on the PCB.

First step: plasma pretreatment process

First, the PCB 12 is positioned between two electrodes 21 connected to a radio frequency (RF) power source 13, that is, a central portion of the reaction chamber 11.

The vacuum pump 20 is then operated to reduce the pressure until the pressure in the reaction chamber is 30 millitorr or less. The pressure in the reaction chamber is regulated through a throttle valve 19, separate from the flow rate of the gas using the flow meter 16.

When the internal pressure of the reaction chamber reaches the target value, the gas for forming the pretreatment plasma is flowed into the reaction chamber at an appropriate flow rate while maintaining the pressure of the reaction chamber at 10 torr, preferably 1 torr or less.

Pretreatment of the PCB surface uses plasma of an inert gas, a reactive gas, or a mixture of an inert gas and a reactive gas, using argon as the inert gas, and oxygen or air as the reactive gas, for example.

An important operating parameter in cold plasma treatment is the energy input per unit mass of pretreated plasma gas, expressed in W / FM (Joule / kg). Where W is the electrical energy input in watts and F and M are the molar flow rates and molecular weights, respectively. FM is therefore a mass flow rate. The electrical energy introduced per mass flow rate of the gas for this pretreatment plasma formation, ie, W / FM, is between 0.1 mega Joule / kg and 50 giga Joule / kg. .

The gas for forming the pretreatment plasma is supplied through a plasma gas supply line and regulates the flow rate with the gas flow meter 16.

The power is then turned on, adjusted to supply the desired level of energy, and then the matching network 14 is activated.

The power supply may be interrupted using the power supply time adjuster 22.

The energy introduced depends on the flow rate of the gas, the size of the sample, the distance between the electrodes, the molecular weight of the pretreatment gas, and the pressure of the reaction system. Plasma pretreatment is typically performed for a total of 30 seconds to 30 minutes, ending with turning off the power supply 13 and closing the gas valve 15.

The pretreatment time depends on the operating variable W / FM, where W / FM is multiplied by the treatment time, ie (energy input) (deposition time) / (mass) is 0.05 mega Joule · min / kg-1,500 giga Joule · min / kg To be

After the plasma pretreatment is completed, the pressure in the reaction chamber is lowered again to 1 millitorr or less with the vacuum pump 20.

The pretreatment may be repeated by changing the gas.

In addition to the above-mentioned RF, the power source may be a direct current (DC) or alternating current (AC) power source, an audio frequency (AF) or a microwave (micro wave).

In addition to the method of FIG. 1, the connection of the power supply may be performed by winding an electrode on the outer wall of the reaction chamber, winding the reaction chamber with a coil, or using a capacitor to generate plasma.

Step 2: depositing the polymer on the PCB surface by plasma polymerization

Deposition of the polymer formed by plasma polymerizing the polymerizable gas on the surface of the PCB to form a polymer thin film, which is a method of operation and apparatus used only in that the supplied gas is a polymerizable gas and the operating conditions of the system differ. Is the same as the plasma pretreatment step of the first step.

In this stage as well as the pretreatment process, the energy supplied is related to the flow rate and molecular weight of the polymerizable gas. The energy introduced per unit mass of polymerizable gas, W / FM, is 0.1 mega Joule / kg to 50 giga Joule / kg.

And while the polymerizable gas is supplied to the reaction chamber, the pressure in the reaction chamber is 1 millitorr to 30 torr, preferably 10 millitorr to 10 torr, more preferably 20 millitorr to 1 torr.

The pressure in the reaction chamber is adjusted using the throttling valve 19 as in the first step, regardless of the flow rate of the gas.

When the gas flow rate and system pressure reach the target, the level of energy supply through the power source is adjusted and the matching network is activated.

At this time, the energy level supplied is determined according to the flow rate and molecular weight of the plasma gas input, the size of the PCB, the distance between the two electrodes, the pressure of the reaction chamber and the like.

The process of depositing the polymer by plasma polymerization proceeds until the polymer thin film formed on the PCB surface has the desired physical properties and thickness. The thickness of the polymer thin film is from 0.005 μm to 100 μm, preferably from 0.1 μm to 1 μm.

The time for depositing the polymer by plasma polymerization varies from 1 second to 1 hour, preferably from 1 minute to 20 minutes, depending on the energy introduced per unit mass.

The step of depositing the polymer by plasma polymerization is controlled by (energy input) x (deposition time) / (mass) as in the plasma pretreatment step, and the value is adjusted from 0.05 mega Joulesec / kg to 1500 giga Joulesec / kg. To be

After the step of depositing the polymer by plasma polymerization, as in the first step, the power source 13 is turned off and the valve 15 is shut off to block the flow of the polymerizable gas.

Efficient plasma polymer deposition is determined by the physical properties of the deposited polymer thin film and the desired thickness of the polymer thin film, and can be repeatedly coated several times by changing the type of gas.

As the polymerizable gas (precursor), a liquid or a solid compound can be used as long as it can form a sufficient vapor pressure under the system pressure. The polymerizable gas for plasma polymerization of the present invention uses an organic material containing carbon as a main raw material and an auxiliary raw material. Hydrogen, oxygen, nitrogen, silane, amine, water vapor, or inert gas.

When plasma polymerized, the main raw material does not maintain its inherent molecular structure in the polymer and can form coatings of similar performance with a variety of raw materials.

Examples of the polymerizable gas having carbon include aliphatic compounds such as methane, ethane and acetylene or derivatives thereof, aromatic compounds such as benzene, toluene and xylene or derivatives thereof, alkaol compounds such as ethanolamine or derivatives thereof, and diethyl Alkylamine compounds such as amines or derivatives thereof, organic silanes or derivatives thereof such as methylsilane, ethylsilane, dimethylsilane and trimethylsilane, organic siloxanes or derivatives thereof such as hexamethyldisiloxane, or butyl diglycidyl ether A compound selected from organic compounds having two or more functional groups bonded to is used.

As the polymerizable gas, aliphatic compounds such as methane, ethane and acetylene or derivatives thereof, aromatic compounds such as benzene, toluene and xylene or derivatives thereof, alcohol compounds such as ethanolamine or derivatives thereof, and diethyl Alkylamine compounds such as amines or derivatives thereof, organic silanes or derivatives thereof such as methylsilane, ethylsilane, dimethylsilane and trimethylsilane, organic siloxanes or derivatives thereof such as hexamethyldisiloxane, or butyl diglycidyl ether The mixture which mixed silane with the compound chosen from the organic compound which couple | bonded two or more functional groups with may be used.

You may use the mixture of 2 or more selected from the said compound.

As the main raw material, a substance containing at least one element of hydrogen, oxygen, nitrogen, silicon, chlorine, and fluorine in addition to carbon in the molecule may be used.

In addition, the coating by the main raw material may be coated by overlapping the plasma polymer of different physical properties one or more times.

Auxiliary raw materials may be added simultaneously with the main raw materials, or may be used before or after coating of the main raw materials. As auxiliary materials, hydrogen, oxygen, nitrogen, amines, water vapor, inert gas, and the like are used.

When the step of depositing the plasma polymer on the PCB surface by plasma polymerization is completed, the pressure in the reaction chamber is lowered back to 10 millitorr or less with the vacuum pump 20 as in the pretreatment step.

As in the plasma pretreatment process, not only the above-mentioned RF but also DC power, AC power, AF or microwave can be used.

Third step: plasma post-treatment process

It is the same as the pretreatment step of the first step and may also be omitted.

The construction of the present invention will become more apparent from the following examples. However, the scope of the present invention is not limited to the embodiment.

<Example 1>

Polymer thin film coating was performed by plasma polymerization using the system shown in FIG. 1, and the specifications of the sample and each component were as follows.

1. PCB board | substrate: The base material manufactured from bismaleimide triazine reinforced with 10 cm x 10 cm glass fiber was used as a sample.

2. Reaction chamber: dome-shaped glass product with inner diameter of 30cm and height of 30cm

3. Power source: An RF power supply (Model RFX-600 from Advanced Energy Industries, Inc.) was used.

4. Electrode: It is installed inside the reaction chamber as shown in Figure 1. The standard is 15x10cm and the distance between two electrodes is 10cm.

(1) Primary pretreatment: The process was treated with argon plasma and the process conditions were RF power 200W, gas flow rate was 6.0 cm ³ / min in standard condition, reaction chamber pressure was 70 millitorr, and treatment time was 10 minutes.

(2) Secondary pretreatment: Oxygen plasma treatment was used, the process conditions were RF power 200W, gas flow rate was 6.0 cm ³ / min in standard condition, the reaction chamber pressure was 70 millitorr, treatment time was 10 minutes.

(3) Primary Plasma Polymer Coating: Hexamethyldisilane was used to coat poly (hexamethyldisilane), process conditions were RF power 300W, gas flow rate 6.0cm ³ / min based on standard condition, reaction chamber pressure 80 millitorr. At this time, the self-bias voltage by the RF power was 120V, the RF power was supplied for 200 minutes and the supply was stopped for 800 minutes for 10 minutes.

(4) Secondary Plasma Polymer Coating: Poly (hexamethyldisilane) was coated with hexamethyldisilane as polymerization gas, process conditions were RF power 200W, gas flow was 6.0cm ³ / min in standard condition, reaction chamber The pressure is 90 millitorr. At this time, the self-bias voltage by RF power was 120V, and RF power was supplied for 10 minutes.

(5) Post-treatment: Oxygen plasma treatment was used, the process conditions were RF power 200W, the gas flow rate was 6.0 cm ³ / min in a standard state, the reaction chamber pressure was 70 millitorr, the treatment time was 10 minutes.

As a result of measuring the shear stress in which the adhesive surface is dropped by injection molding the EMC on the PCB treated as described above, the PCB etched with argon plasma was measured as 20KG / cm ² compared with 10KG / cm ² .

<Example 2>

As in Example 1, the apparatus shown in FIG. 1 was used.

(1) Primary pretreatment: The process was treated with argon plasma and the process conditions were RF power 200W, gas flow rate was 6.0 cm ³ / min in standard condition, reaction chamber pressure was 70 millitorr, and treatment time was 10 minutes.

(2) Secondary pretreatment: Oxygen plasma treatment was used, the process conditions were RF power 200W, gas flow rate was 6.0 cm ³ / min in standard condition, the reaction chamber pressure was 70 millitorr, treatment time was 10 minutes.

(3) Primary Plasma Polymer Coating: Poly (acetylene) was coated with acetylene as polymerization gas, process conditions were RF power 100W, gas flow rate was 9.0cm ³ / min based on standard condition, and reaction chamber pressure was 70 millitorr. . At this time, the self-bias voltage by RF power was 120V and RF power was supplied.

(4) Secondary Plasma Polymer Coating: Poly (acetylene) was coated with acetylene as polymerization gas, process conditions were RF power 150W, gas flow rate was 9.0cm ³ / min based on standard condition, and reaction chamber pressure was 75 millitorr. . At this time, the self-bias voltage by RF power was 120V, and RF power was supplied for 10 minutes.

(5) Post-treatment: The PCB was placed in a vacuum tube and treated with oxygen. The process conditions were RF power 200W, the gas flow rate was 6.0 cm ³ / min in standard condition, the reaction chamber pressure was 70 millitorr, and the treatment time was 10 minutes.

As a result of measuring the shear stress in which the adhesive surface is dropped by injection molding EMC on the PCB treated as described above, the PCB etched with argon plasma was measured at 18KG / cm ² , compared to 10KG / cm ² .

As described above, when the polymerizable gas is coated at a low temperature plasma to coat the surface of the PCB, adhesion to the EMC may be increased, thereby lowering a defect rate of the semiconductor chip to be manufactured.

Claims (11)

EMC used as PCB and encapsulant by coating a thin film of plasma polymer produced by plasma polymerizing polymerizable gas on the surface of PCB (Printed Circuit Board) used for packaging semiconductor by BGA (Ball Grid Array) method How to improve the adhesion with the. The method of claim 1, wherein the polymerizable gas is an aliphatic compound or derivative thereof, an aromatic compound or derivative thereof, an alcoholic compound or derivative thereof, an alkylamine compound or derivative thereof, an organic silane or derivative thereof, an organosiloxane or the like A method of improving adhesion between a PCB and an EMC used as an encapsulant by coating a plasma polymer with a thin film using a derivative or a compound having a carbon source selected from organic compounds having two or more functional groups bonded thereto. The method of claim 1, wherein the polymerizable gas is an aliphatic compound or derivative thereof, an aromatic compound or derivative thereof, an alcoholic compound or derivative thereof, an alkylamine compound or derivative thereof, an organic silane or derivative thereof, an organosiloxane or the like A method of improving adhesion between a PCB and an EMC used as an encapsulant by coating a plasma polymer with a thin film, characterized in that a mixture of a silane and a compound selected from derivatives or organic compounds having two or more functional groups bonded together. The method according to claim 2, wherein the plasma polymer is coated with a thin film, wherein the compound selected from methane, ethane, and acetylene is used as the aliphatic compound to improve adhesion between the PCB and the EMC used as an encapsulant. The method of claim 2, wherein the plasma polymer is coated with a thin film, wherein the compound selected from benzene, toluene, and xylene is used as the aromatic compound to improve adhesion between the PCB and the EMC used as an encapsulant. 3. The method of claim 2, wherein the plasma polymer is coated with a thin film, using ethanolamine as an alcohol-based compound, to improve adhesion between the PCB and EMC used as an encapsulant. The method of claim 2, wherein the plasma polymer is coated with a thin film using diethylamine as the alkylamine compound to improve adhesion between the PCB and the EMC used as an encapsulant. The method of claim 2, wherein a compound selected from methylsilane, ethylsilane, dimethylsilane, and trimethylsilane is used as the organic silane to coat the plasma polymer with a thin film to improve adhesion between the PCB and EMC used as an encapsulant. Way. The method of claim 2, wherein the plasma polymer is coated with a thin film, characterized in that hexamethyldisiloxane is used as the organic siloxane, to improve adhesion between the PCB and the EMC used as an encapsulant. The method of claim 2, wherein the butyl diglycidyl ether is used as an organic compound having two or more functional groups bonded thereto, and the plasma polymer is coated with a thin film to improve adhesion between the PCB and the EMC used as an encapsulant. A PCB manufactured by the method of any one of claims 1 to 10.