Die bonding apparatus comprising an inert gas environment

A die bonding apparatus comprising a first inert gas container having a first inert gas concentration, and a second inert gas container having a second inert gas concentration enclosed within the first inert gas container. The second inert gas concentration is higher than the first inert gas concentration. The die bonding apparatus further comprises a bond head located in the second inert gas container for receiving a die for bonding, and a third inert gas container having an inert gas environment that is separate from the first and second inert gas containers and where a substrate is locatable for die bonding. The bond head is operative to move the die between a first position within the second inert container and a second position within the third inert gas container to bond the die onto the substrate located in the third inert gas container.

FIELD OF THE INVENTION

The invention relates to a die bonding apparatus, and in particular to a die bonding apparatus comprising an inert gas environment to conduct die bonding.

BACKGROUND

Assembly of an integrated circuit (IC) when manufacturing an electronic package involves attaching a die or chip to a substrate. One example of a bonding process is the thermal compression bonding (TCB) process, which may be used for flip-chip bonding. The TCB process is not a batch process, unlike a conventional oven reflow process. The bonding of a flip-chip die during a TCB process is performed one die at a time. The die from the silicon wafer is flipped and transferred to a bond-arm with bumps on the die facing down. The die carried by the bond-arm is then placed onto a bonding location of the substrate or onto another die. A small compressive force is applied onto the die to press it against the substrate or the other die to ensure good contact between the die and the substrate or between the respective dice.

Impurities on bonding materials are undesirable because impurities prevent good contact between the bonding materials and bonding surfaces, which may result in performance degradation of final products. There are many potential sources of impurities in a die bonding process. For example, impurities may originate from foreign materials covering the surface of the bonding materials, arise from oxidation of the bonding materials under high temperature during the TCB process, or result from by-products generated during the bonding process.

It would be beneficial to reduce the amount of impurities which may interfere with the bonding process to avoid performance degradation of assembled electronic packages.

SUMMARY OF THE INVENTION

It is thus an object of this invention to seek to provide a die bonding apparatus which is able to reduce the amount of impurities in order to avoid performance degradation of assembled electronic packages.

According to the invention, there is provided a die bonding apparatus comprising a first inert gas container having a first inert gas concentration; a second inert gas container having a second inert gas concentration enclosed within the first inert gas container, the second inert gas concentration being higher than the first inert gas concentration; a bond head located in the second inert gas container for receiving a die for bonding; and a third inert gas container having an inert gas environment that is separate from the first and second inert gas containers and where a substrate is locatable for die bonding. The bond head is operative to move the die between a first position within the second inert container and a second position within the third inert gas container to bond the die onto the substrate located in the third inert gas container.

These and other features, aspects, and advantages will become better understood with regard to the description section, appended claims, and accompanying drawings.

In the drawings, like parts are denoted by like reference numerals.

DETAILED DESCRIPTION

FIG. 1is a plan view of a die bonder10according to the preferred embodiment of the present invention. The die bonder10comprises a transfer system, such as a highway transfer system12which is configured to transport a bonding substrate or die package to a location where a substrate transfer arm (STA) head16of a substrate transfer arm (STA)14is operative to pick up the substrate. The substrate is supplied to the highway transfer system12from a substrate supply13. The STA14, which is movable in an X axis, is configured to transport the substrate and place it onto a bond stage60at a loading position. The bond stage60, which is movable along X-Y axes, is movable below a first inert gas container or macro inert environment40. The macro inert environment40has a first inert gas concentration. The macro inert environment40comprises a second inert gas container or core inert environment50which has a second inert gas concentration. The second inert gas concentration has a higher concentration of inert gas than the first inert gas concentration. In other words, the core inert environment50, which is located within the macro inert environment40, has a lower oxygen concentration than the macro inert environment40. The bond stage is locatable below the macro inert environment40and the core inert environment50. The bond stage60is configured to transport the substrate from the loading position where the substrate is loaded onto the bond stage60, to a bonding position below the core inert environment50where die bonding is performed. A cleaning system (not shown) may be used to clean the substrate before the bond stage60moves the substrate below the macro inert environment40.

A die pick arm (DPA) head22of a die pick arm (DPA)20is configured to pick up a die from a semiconductor dice supply15. The DPA20is configured to transport the die to a die transporter or die transfer arm (DTA)30located within the macro inert environment40. The DTA30is configured to transport the die to a pick-up position within the macro inert environment40to be picked up by the bond head52. The transportation of the substrate and the die to the bonding position may be performed simultaneously.

FIG. 2is a side view of an inert environment system90for performing die bonding. In particular, the inert environment system90protects a die24and a substrate26from impurities and oxidation, especially when the temperatures of the die24and the substrate26are high, for example before, during, and after bonding. The inert environment system90comprises the macro inert environment40, the core inert environment50within the macro inert environment40, and a third inert gas container or micro inert environment80located below the macro inert environment40. The micro inert environment80has an inert gas environment that is separate from the macro inert environment40and the core inert environment50. The micro inert environment80is mounted on the bond stage60, where the substrate26is locatable for die bonding.

The macro inert environment40comprises a macro inert chamber44, and a macro inert chamber base plate42covering the bottom of the macro inert chamber44. The macro inert chamber44further comprises a DTA opening32on a side wall of the macro inert chamber44. The DTA opening32is configured to allow the DPA20to transfer the die24to the DTA30. The macro inert chamber base plate42comprises a first container opening or bond exhaust window (BEW) opening70located generally at a centre of the macro inert chamber base plate42. The core inert environment50comprises a second container opening74aligned to the BEW opening70and the pick-up position, such that the bond head52is able to move to the pick-up position in the macro inert environment40to pick up the die24from the DTA30. The second container opening74and the BEW opening70are also aligned to the bonding position, such that the bond head52is able to move to the bonding position to bond the die24to the substrate26. The BEW opening70and the second container opening74fluidly connect the macro inert environment40, the core inert environment50, and the micro inert environment80. The macro inert environment40provides a low-oxygen inert environment to protect the die24, which usually has not yet been heated for bonding while moving the die24to the pick-up position. The macro inert environment40does not have a direct inert gas supply, but is generally passively filled with inert gas which overflows from the core inert environment50and/or the micro inert environment80. The macro inert environment40may further include inspection optics to perform pre-bonding and/or post-bonding inspection.

The core inert environment50comprises a core inert chamber54with the second container opening74at the bottom thereof. A bond head52is located within the core inert environment50. The core inert environment50is located generally above the BEW opening70. The bond head52is operative to move the die24from a first position within the core inert environment50to a second position within the micro inert environment80in order to bond the die24onto the substrate26located within the micro inert environment80. The DTA30is configured to transport the die24to below the bond head52, in order for the bond head52to pick up the die24. The bond head comprises a bond head heater (not shown) for heating the die24to a bonding temperature. A high concentration of an inert gas, for example nitrogen, is continuously supplied into the core inert environment50to keep the concentration of oxygen as low as possible, in order to protect the die24from oxidation when it is heated by the bond head52.

The bond stage60comprises a bond stage heater46, a bond stage pedestal66located on the bond stage heater46, and walls62along the periphery of the bond stage60. The bond stage pedestal66is configured to hold the substrate26, and the bond stage heater46is configured to heat the substrate26for bonding. The micro inert environment80is formed when the bond stage60moves below the macro inert environment40. The micro inert environment80primarily comprises a portion of the bond stage60that is enclosed by the walls62on the sides, by the bond stage pedestal66on the bottom, and by the macro inert chamber base plate42on the top. There is a gap between the walls62and the macro inert chamber base plate42, which allows the micro inert environment80to freely move around below the macro inert environment40. The micro inert environment80provides a low-oxygen inert environment to protect the substrate26when it is heated up by the bond stage heater46, for example when transporting the substrate26to the bonding position below the core inert environment50. When the micro inert environment80is below the core inert environment50, some of the inert gas flows from the core inert environment50to the micro inert environment80, thus providing a supply of inert gas to the micro inert environment80.

FIG. 3is a perspective view of part of the inert environment system90ofFIG. 2, including a movable bond stage60for receiving a substrate26to be processed. The movable bond stage60comprises an XY table. The walls62comprise bond stage inert gas outlets64which surround or enclose the sides of the micro inert environment80in a manifold structure. The DTA opening32is configured to allow the DPA20to transfer the die24to the DTA30. The DPA20is operative to extend through the d DTA opening32to transfer the die to the DTA30. The transfer of the die24by the DPA20into the macro inert environment40is usually performed as fast as possible to reduce the time the die24is exposed to ambient air, in order to minimize oxidation of the die24. In order to minimize gaseous exchange between the macro inert environment40and the ambient air, a door (not shown) may be provided at the DTA opening32. The door may comprise a mechanical shutter door, which opens only when the DPA20is transferring the die24to the DTA30, and which remains closed at other times.

FIG. 4is a perspective view of the core inert environment50comprised in the inert environment system90. The core inert chamber54may include a transparent window58at a side wall, in order to allow a user to look into the core inert environment50. The core inert environment50comprises a high concentration of inert gas and a low concentration of oxygen, for preventing oxidation when the die24is heated by the bond head52to a high temperature where oxidation occurs more readily. Inert gas is actively and directly supplied to the core inert environment50to maintain the high concentration of inert gas and low concentration of oxygen. The core inert chamber54comprises inert gas inlets34for supplying inert gas to the core inert environment50, a plurality of inert gas outlets or diffusers36connected to the inert gas inlets34, and a flow channel plate38for delivering inert gas from the inert gas inlets34to the diffusers36. The flow channel plate38, which covers the top of the core inert chamber54, comprises four peripheral side walls which define a bond head opening56for locating the bond head52. A gasket layer37is placed on a top surface of the flow channel plate38. The diffusers36are located alongside two opposite peripheral side walls of the flow channel plate38.

FIG. 5is a sectional view of an exemplary gas-flow comprised in the core inert environment50. An inert gas supply (not shown) is connected to the core inert environment50via the inert gas inlets34to supply inert gas to the core inert environment50. Inert gas flows in from the inert gas inlets34to the flow channel plate38, and then to the diffusers36. The diffusers36, which are spaced equally apart, evenly distribute the inert gas into the core inert environment50. The diffusers36direct a laminar downward inert gas flow around the bond head52and the die24and towards the second container opening74at the bottom of the core inert environment50. The diffusers36may be configured to slow down the flow speed of the inert gas, in order to better create the laminar downward flow as well as a uniform concentration of inert gas within the core inert environment50. In this way, a suitable environment is created for bonding and to protect the heated die24from oxidation.

The core inert environment50is directly above the BEW opening70of the macro inert chamber base plate42. When the micro inert environment80is positioned to the bonding position, the micro inert environment80is directly below the core inert environment50and the BEW opening70. The inert gas from the diffusers36fills up the core inert environment50, and flows downwards towards the BEW opening70.

FIG. 6shows a perspective view of the bond stage60illustrating an air-flow generated therefrom. The bond stage60comprises the walls62which comprise the bond stage inert gas outlets64surrounding the micro inert environment80in a manifold structure. The bond stage inert gas outlets64comprises outer inert gas outlets69, which direct inert gas upwards, thereby forming a shield or air curtain above the bond stage inert gas outlets64. The bond stage60also comprises inner micro inert chamber gas outlets68which supply inert gas into the micro inert environment80. The bond stage60further comprises an additional storage space65between one of the walls62and the position where the substrate26is locatable for die bonding. The additional storage space65may, for example, be used as a nozzle bank to store different nozzles for picking up different dice. The bond head52may change to a different nozzle which is mountable onto the bond head52anytime during the bonding process, while the bond head52and the nozzles are being protected by the core inert environment50and the micro inert environment80.

FIG. 7is a side view of the micro inert environment80comprised in the inert environment system90. The movable micro inert environment80is created when the bond stage60moves below the macro inert environment40. The micro inert environment80primarily comprises a portion of the bond stage60that is enclosed by the walls62on the sides, by the bond stage pedestal66on the bottom, and by the macro inert chamber base plate42on the top. There is a gap between the bond stage inert gas outlets64of the walls62and the macro inert chamber base plate42of the macro inert environment40, so that the micro inert environment80may freely move below the macro inert environment40and relative to the macro inert environment40and the core inert environment50. The outer inert gas outlets69expels inert gas towards the macro inert chamber base plate42of the macro inert environment40to form the shield or air curtain to restrict ambient air from entering the micro inert environment80. The air curtain, formed by the inert gas flowing from the outer inert gas outlets69, is designed to restrict gaseous exchange between the micro inert environment80and the ambient air. The inert gas from the outer inert gas outlets69flows directly to the macro inert chamber base plate42, and the inert gas flow splits up such that a first portion of the inert gas flow is directed outwards to the ambient air and a second portion of the inert gas flow is directed inwards into the micro inert environment80. In this manner, the air curtain restricts ambient air from entering into the micro inert environment80, even when the micro inert environment80is moving below the macro inert environment40.

The micro inert environment80serves to protect the substrate26from oxidation. The substrate26is placed on the bond stage60in the ambient air environment, but when the bond stage60moves below the macro inert environment40, the micro inert environment80is created. When the micro inert environment80is created, the substrate26may be heated up safely, because the micro inert environment80protects the substrate26from oxidation during transportation below the macro inert environment40, and during bonding.

FIG. 8illustrates a flux exhaust system incorporated in the die bonder. During bonding, the bond head52holding the die24heats up the die24to an appropriate temperature for bonding, and moves downwards towards the substrate26which has been heated up by the bond stage heater46to an appropriate temperature for bonding. The bond head52moves downwards through the BEW opening70and the second container opening74, until the die24contacts the substrate26. The die24is then bonded to the substrate26under high temperature, and vaporized flux is generated during bonding. The flux exhaust system comprising a flux exhaust inlet72, a vapor condenser (not shown) connected to the flux exhaust inlet72, and a storage collector (not shown) connected to the vapor condenser, is configured to remove the vaporized flux. The macro inert chamber base plate42comprises a first plate76comprising a first hole77, and a second plate78comprising a second hole79aligned with the first hole77. The first hole77and the second hole79together forms the BEW opening70. The flux exhaust inlet72is located at the BEW opening70, and the flux exhaust inlet72comprises the space in-between the first plate76and the second plate78. The vaporized flux may enter the flux exhaust inlet72from the BEW opening70in-between the first plate76and the second plate78. The flux exhaust inlet72may for example be circular in shape, such that the vaporized flux enters the circular shaped flux exhaust inlet72from all directions. The flux exhaust system produces a suction force to extract the vaporized flux generated during bonding into the flux exhaust inlet72, and thereafter expels the flux exhaust from the flux exhaust system.

The flux exhaust system is also configured to extract the ambient air when the micro inert environment80is not below the BEW opening70, such that ambient air is prevented from entering into the micro inert environment80when the micro inert environment80is not below the BEW opening70. In addition, the flux exhaust system is configured to extract the ambient air in the micro inert environment80when the micro inert environment80moves below the BEW opening70. Furthermore, the flux exhaust system may be configured to correlate with inert gas supplies to the micro inert environment80, such that the ambient air is prevented from entering into the micro inert environment80even without the air curtain formed by the inert gas flowing from the outer inert gas outlets69.

The concentration of oxygen in the macro inert environment40may vary widely, but is usually from 50 ppm (parts per million) to 100 ppm. The concentration of oxygen in the core inert environment50may also vary widely, but is usually from 0 ppm to 50 ppm. The concentration of oxygen in the micro inert environment80may further vary widely, but is usually from 0 ppm to 50 ppm.

Although the present invention has been described in considerable detail with reference to certain embodiments, other embodiments are possible.

For example, instead of the door at the DTA opening32, an inert gas air curtain may be provided to minimize gaseous exchange between the macro inert environment40and the ambient air.

Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.