WO2006036037A1

WO2006036037A1 - Deflashing apparatus and method for semiconductor packages

Info

Publication number: WO2006036037A1
Application number: PCT/KR2004/003063
Authority: WO
Inventors: You-Hie Han; Eun-Jeong Hong; Tae-Kyoung Ryoo
Original assignee: Eo Technics Co., Ltd.
Priority date: 2004-09-30
Filing date: 2004-11-25
Publication date: 2006-04-06
Also published as: KR100475750B1

Abstract

The object of the present invention is to provide a deflashing apparatus and method to remove mold flash from a semiconductor package using a laser. The present invention forms a frozen layer on a surface of a semiconductor package using water vapor in the atmosphere, after a molding process is completed, and a CO2 laser is irradiated onto the frozen layer formed on mold flash. As the CO2 laser is absorbed by the frozen layer, a large quantity of water vapor is generated. As the vapor rapidly expands, an impulse wave is generated in a direction opposite to a vapor generating direction, thus removing the mold flash using the impulse wave. Therefore, the present invention allows the mold flash to be easily removed, and because the laser beam is not directly irradiated to the mold flash, a semiconductor package with high reliability and superior packaging can be manufactured.

Description

DEFLASHING APPARATUS AND METHOD FOR SEMICONDUCTOR PACKAGES

Technical Field

The present invention relates, in general, to an apparatus and method of removing mold flash and, more particularly, to a deflashing apparatus and method intended to remove mold flash, from a semiconductor package using a laser.

Background Art

A semiconductor package is produced through molding after forming input and output terminals to be connected to an exterior main board, using a lead frame or a printed circuit board (PCB), thus protecting semiconductor chips, such as a single device provided by laminating various electronic circuits and wires or an integrated circuit, against external conditions including dust, humidity, and electric and mechanical load, and optimizing and maximizing electric performance of the semiconductor chips.

Recently, as high integration and high performance of semiconductor chips are achieved, and miniaturization and high functionality of electronic products are also achieved, lightness, thinness, compactness, smallness, and high pin count of a semiconductor package are required. Further, there is a tendency to reduce manufacturing costs of the semiconductor chips, by simplifying the manufacturing process and increasing productivity.

FIG. 1 is a view illustrating an appearance of a conventional semiconductor package.

As shown in the drawing, the semiconductor package 10 is configured such that a plurality of semiconductor chips 12 is connected to a lead frame 14 which is made of a metal material. In order to manufacture the semiconductor package 10, the semiconductor chips 12 are covered with a protective material, such as an Epoxy Molding Compound (EMC). Such a process is designated as a molding process. However, molding compound frequently adheres to the lead frame 14 during the molding process, and the adhered molding material is called "mold flash". FIG. 2 is a view illustrating a state where the mold flash remains on the semiconductor package.

As shown in the drawing, while molding the semiconductor chip 12, the mold flash 16 may be formed on the lead frame 14. Since the mold flash 16 causes the malfunction of a circuit, the mold flash 16 must be removed. Thus, in order to remove the mold flash 16, a method of irradiating a laser onto the mold flash has been used.

In a detailed description, a laser beam is focused on the mold flash 16 to bum the mold flash 16, and then a cleaning operation is performed using a water jet. However, this method has a problem that for the laser beam is directly irradiated onto the lead frame 14, the color may be undesirably changed. Such a problem is more serious when the semiconductor package is white. Further, according to the conventional method, the laser beam is irradiated, with the semiconductor package exposed. Thus, this method has another problem that the semiconductor chip or the lead frame is damaged if the laser beam is not precisely irradiated onto the mold flash, making the production efficiency of the semiconductor package reduced.

Disclosure of the Invention

Accordingly, the present invention has been made to solve the above problems in the prior art, and an object of the present invention is to provide a deflashing apparatus and method, capable of removing mold flash of a semiconductor package, and minimizing harm to a lead frame during the fabrication of the semiconductor package. In order to accomplish the above object, the present invention forms a frozen layer on a surface of a semiconductor package using water vapor contained in the atmosphere, after a molding process is completed, and irradiate a laser onto the frozen layer formed on mold flash. In this case, it is preferable that a CO₂ laser be used as the laser. The present invention removes the mold flash, using the following principle. That is, when the CO₂ laser is absorbed by the frozen layer, a large quantity of water vapor is generated. As the water vapor rapidly expands, an impulse wave is generated in a direction opposite to a vapor generating direction.

Since the mold flash maintains a cooled state when the mold flash is removed, the removal efficiency is maximized. Further, since a laser beam does not burn the mold flash but impacts on the mold flash to remove it, the semiconductor package can maintain an excellent appearance.

Further, the present invention uses a thermoelectric module to form the frozen layer on the surface of the semiconductor package, and forms the frozen layer by cooling water vapor in a chamber on the surface of the semiconductor package, thus efficiently removing the mold flash of the semiconductor package without incurring great expense.

Brief Description of the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view illustrating the appearance of a conventional semiconductor package; FIG. 2 is a view illustrating a state where mold flash remains on the semiconductor package;

FIG. 3 is a block diagram illustrating the construction of a deflashing apparatus, according to the present invention; FIGS. 4A and 4B are views illustrating thermoelectric modules adapted to the present invention; and

FIG. 5 is a flow chart illustrating a deflashing method, according to the present invention.

Best Mode for Carrying Out the Invention

Hereinafter, the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a block diagram illustrating the construction of a deflashing apparatus, according to the present invention.

As shown in the drawing, a semiconductor package deflashing apparatus 100 includes a control unit 110, a laser generating means 120, a reflecting means 130, an input unit 140, a display unit 150, and a storage unit 160. The control unit 110 controls the entire operation of the deflashing apparatus 100. The laser generating means 120 generates a laser beam having a predetermined caliber. The reflecting means 130 changes the direction of the laser beam generated by the laser generating means 120, thus focusing the laser beam on a predetermined position of the semiconductor package. The input unit 140 is used to input a control parameter and a control instruction. The display unit 150 displays information, such as an operational state. The storage unit 160 serves to store data. The deflashing apparatus 100 also includes a chamber 170 into which a semiconductor chip to be deflashed is loaded, a holding means 30 which holds a semiconductor package 10, a thermoelectric module (TEM) 40 which cools the holding means 30, and an insulation means 50 which prevents several mechanical units, such as a coupling member 60, from being cooled by the TEM 40. The holding means 30, the TEM 40, and the insulation means 50 form a stage on which the semiconductor package 10 is supported. The coupling member 60 is coupled to, for example, a stage conveying means (not shown) to convey the stage having the semiconductor package 1, thus deflashingthe semiconductor package 10.

In this case, the TEM 40 is a functional electronic element which directly changes heat energy to electric energy or change electric energy to heat energy. The TEM 40 is also known as a

Peltier element. The Peltier element serves as a thermal engineering element to transfer heat from a heat absorbing part to a heat evolving part. The Peltier element is advantageous in that conversion from a cooling operation to a heating operation is allowed by changing a thermoelectric direction, and the Peltier element is controlled not. by an on/off control but by voltage or current, so that fine temperature control is possible. Further, since the Peltier element has no moving parts, no vibration or noise are generated. Furthermore, the Peltier element does not use a Freon refrigerant, so that pollution is prevented.

FIGS. 4A and 4B are views illustrating thermoelectric modules adapted to the preset invention.

As shown in the drawings, the TEM 40 includes lower conductive layers 420 and upper conductive layers 422 between a lower substrate 410 and an upper substrate 412. Semiconductor chips 430 are provided between the lower conductive layers 420 and the upper conductive layers 422. As electricity is supplied to power supply cables 440 and 442, a cooling operation is executed.

In this case, the lower and upper substrates 410 and 412 serve to limit the flow of electricity, in addition to efficiently transmitting heat. The lower and upper conductive layers 420 and 422 and the semiconductor chips 430 actually act as a cooling engine. Further, the semiconductor chips 430 are arranged such that P-type semiconductors and N-type semiconductors are connected to each other in series, thus maximizing cooling efficiency.

FIG. 4B shows another thermoelectric module. In this thermoelectric module, a plurality of holes 450 is formed on the upper substrate 412. The holes 450 are used to efficiently transmit cool air, generated between the semiconductor chips 430 and the conductive layers 420, 422, to an object placed on the upper substrate 412. As the TEM 40 begins the cooling operation, the holding means 30 provided on the TEM 40 is cooled. As a result, the temperature of the semiconductor package 10 is lowered. Because, the interior of the chamber 170 is at room temperature. Thus, as the temperature of the semiconductor package 10 is lowered, water vapor is condensed due to the temperature difference between the interior of the chamber 170 and the semiconductor package 10. Thereby, dew forms on the surface of the semiconductor package 10. In such a state, as the TEM 40 continues the cooling operation, a frozen layer 20 forms on the surface of the semiconductor package 10. For such a process, it is preferable that the holding means 30 be made of a material having excellent heat conductivity, for example, a metal. Further, the holding means 30 is configured such that an upper surface thereof is flat, and the semiconductor package 10 is mounted on the flat upper surface of the holding means 30, thus allowing cool air to be rapidly transmitted to the semiconductor package 10. Alternatively, the holding means 30 may be configured to hold only a guide part of the semiconductor package 10 so that cool air transmitted to the holding means 30 is gradually transmitted from the guide part to an interior of the semiconductor package 10. In this case, the lead frame 14 of the semiconductor package 10 is made of a metal material, and a semiconductor chip 12 is covered with a plastic material, such as an EMC. Therefore, the frozen layer 20 is formed on a surface of the lead frame 14, and then subsequently formed on a surface of the EMC which covers the semiconductor chip 12 as well as on a surface of the mold flash. When a laser beam is irradiated onto the mold flash of the semiconductor package 10, moisture present in the frozen layer 20 rapidly expands. Thus, the frozen layer 20 serves to generate an impulse wave that removes the mold flash. Preferably, a CO₂ laser is adapted to the deflashing apparatus in the present invention. The CO₂ laser is easily absorbed by the frozen layer 20. When the CO₂ laser is irradiated onto the frozen layer 20, a large quantity of water vapor is produced on the surface onto which the laser beam is irradiated. Such water vapor rapidly expands on the laser irradiated surface, making an impulse wave is generated in a direction opposite to a vapor generating direction.

That is, all of the CO₂ laser irradiation is absorbed by the frozen layer 20, so the CO₂ laser is not directly applied to the mold flash. Thus, the mold flash is removed, by the impulse wave resulting from the expansion of the moisture. As such, since the mold flash is not burned by the laser beam, a change in color of the semiconductor package is prevented. Moreover, when the laser beam is irradiated, the mold flash maintains a cooled state, so that brMeness is increased, thereby the mold flash is more efficiently removed.

Further, in order to reduce the time required to cool the semiconductor package 10 by the

TEM 40 after loading the semiconductor package 10 into the chamber 170, it is possible to load the semiconductor package 10 into the chamber 170 after preliminarily cooling the semiconductor package 10. In this case, moisture present between the semiconductor package 10 and the holding means 30 may freeze after the semiconductor package 10 is loaded into the chamber 170. Thus, it is preferable that a preliminary cooling temperature be set higher than a condensation point. The condensation point is the temperature at which water vapor begins to condense into water. The condensation point varies depending on the surrounding humidity and is proportional to the surrounding humidity.

According to the present invention, the frozen layer 20 is formed on the surface of the semiconductor package 10, using the temperature difference between the interior of the chamber 170 and the semiconductor package 10. When a laser beam is irradiated onto the frozen layer 20, the moisture rapidly expands and the impulse wave is generated in a direction opposite to the vapor generating direction. Thereby, the mold flash is removed using the impulse wave.

Further, the thickness of the frozen layer 20 formed on the surface of the semiconductor package 10 varies depending on the internal humidity of the chamber 170. The humidity varies depending on the temperature. According to the present invention, the sensor 180 is mounted within the chamber 170 to detect the temperature and humidity in the chamber 170, thus regulating the thickness of the frozen layer 20. Since the internal humidity of the chamber 170 is usually low, it is not necessary to be concerned about an increase in thickness of the frozen layer 20 due to excessive humidity. When the internal humidity of the chamber 170 detected by the sensor 180 is lower than a predetermined level, the moisture in the air in the chamber 170 is insufficient, so the sufficiently thick frozen layer 20 is not formed. Thus, in order to solve the problem, the humidifying means 190 is provided, thus supplying moisture to the air in the chamber 170.

FIG. 5 is a flow chart illustrating a deflashing method according to the present invention. When a process of manufacturing the semiconductor chip, such as a single device or an integrated circuit, is completed, a molding process is executed to protect the semiconductor chip against the environment and maximize electric performance, so that the semiconductor package 10 is manufactured at step SlO. When the molding process is carried out to manufacture the semiconductor package 10, mold flash may be generated. Since the mold flash causes defectiveness in the device, the mold flash must be removed. In order to remove the mold flash, the semiconductor package 10 is loaded into the chamber 170 and held by the holding means 30, at step S20.

Further, a control parameter is set at step S30, considering the shape of the semiconductor package 10 and the portion where the mold flash exists. For easy parameter setting, menu items are preset and stored in the storage unit 160. Thereafter, the menu items are called, as necessary.

When the control parameter setting operation is completed, the TEM 40 is driven to cool the semiconductor package 10. Thus, the frozen layer 20 is formed on the surface of the semiconductor package 10 at step S40. The semiconductor package 10 may be cooled by the TEM 40, after being loaded into the chamber 170. However, in order to shorten the cooling time, the semiconductor package 10 may be loaded into the chamber 170 after being preliminarily cooled. Ih this case, as described above, it is preferable that the semiconductor package 10 be preliminarily cooled to a temperature which is higher than the condensation point, thus preventing moisture present between the semiconductor package 10 and the holding means 30 from freezing.

Meanwhile, when the internal humidity of the chamber 170 detected by the sensor 180 is lower than a predetermined level, the humidifying means 190 supplies moisture to the air in the chamber 170, to form the sufficiently thick frozen layer 20. Thereafter, the stage conveying means is driven to convey the stage having the semiconductor package 10 at a predetermined speed, and the control unit 110 controls the laser generating means 120 to generate the laser at step S50. At this time, the laser beam generated by the laser generating means 120 is reflected by the reflecting means 130 and is irradiated onto the surface of the semiconductor package 10 to remove the mold flash at step S60. That is, the CO₂ laser beam which is generated by the laser generating means 120 and reflected by the reflecting means 130 is irradiated onto the frozen layer 20 formed on the mold flash. At this time, the CO₂ laser is absorbed by the frozen layer 20, and a large quantity of water vapor is generated. The water vapor rapidly expands, and the impulse wave is generated in a direction opposite to the vapor generating direction, thus removing the mold flash from the lead frame 14. According to the present invention, the laser beam does not directly act on the mold flash or the lead frame to which the mold flash is attached, thus preventing the color of the semiconductor package from being changed due to the combustion by the laser beam. Further, because the mold flash is removed while maintaining a cooled state, removal efficiency is maximized.

It is understood by those skilled in the art that the present invention may be embodied in several forms without departing from the spirit and the essential characteristics of the invention. Therefore, the present embodiment is illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within meanings and bounds of the claims, or equivalence of such meanings and bounds are therefore intended to be embraced by the claims. Industrial Applicability

As described above, the present invention provides a deflasbing apparatus and method, which forms a frozen layer on a surface of a semiconductor package and irradiates a CO₂ laser beam onto the frozen layer provided on the surface of the semiconductor package, thus generating an impulse wave, therefore efficiently removing the mold flash generated during the fabrication of the semiconductor.

Further, the laser beam is not directly irradiated onto the mold flash, thus preventing the mold flash from being burnt, therefore preventing the color of the semiconductor package from being changed, and accomplishing a semiconductor package with high reliability and a superior packaging.

Claims

1. A deflashing apparatus for a semiconductor package, intended to remove mold flash from the semiconductor package which is manufactured by molding a semiconductor chip connected to a lead frame, the deflashing apparatus comprising: holding means to hold the semiconductor package loaded into a process chamber; a thermoelectric module mounted to a lower surface of the holding means, the thermoelectric module cooling the semiconductor package via the holding means, thus forming a frozen layer on a surface of the semiconductor package; laser generating means to generate and output a laser beam having a predetermined caliber; and reflecting means to reflect the laser beam generated by the laser generating means onto the semiconductor package.

2. The deflashing apparatus according to claim 1, wherein the laser generated by the laser generating means is a CO₂ laser.

3. The deflashing apparatus according to claim 1, further comprising: a sensor to detect temperature and humidity in the chamber.

4. The deflashing apparatus according to claim 3, further comprising: humidifying means to supply water vapor to air in the chamber, when the sensor detects that the humidity in the chamber is lower than a predetermined level.

5. The deflashing apparatus according to claim 1 , further comprising: insulation means provided on a lower surface of the thermoelectric module.

6. The deflashing apparatus according to claim 1, wherein the holding means comprises a metal.

7. A deflashing method for a semiconductor package, intended to remove mold flash from the semiconductor package which is manufactured by molding a semiconductor chip connected to a lead frame, the deflashing method comprising the steps of: loading the semiconductor package into a chamber after holding the semiconductor package on holding means, with a thermoelectric module mounted to a lower surface of the holding means; setting a control parameter according to a shape of the semiconductor package and a portion where the mold flash exists; forming a frozen layer on a surface of the semiconductor package, by driving the thermoelectric module to cool the semiconductor package held on the holding means; conveying the semiconductor package; and irradiating a laser beam onto the portion having the mold flash which is formed on the surface of the semiconductor package.

8. The deflashing method according to claim 7, wherein the laser beam is a CO₂ laser beam.

9. The deflashing method according to claim 7, further comprising: preliminarily cooling the semiconductor package to a temperature which is higher than a condensation point, prior to loading the semiconductor package into the chamber.

10. The deflashing method according to claim 7, wherein the step of forming the frozen layer is executed after supplying water vapor to air in the chamber, when it is detected that humidity in the chamber is lower than a predetermined level.

11. The deflashing method according to claim 7, wherein the holding means comprises a metal.