Patent Publication Number: US-10312214-B2

Title: Atomization mechanism for cooling a bond head

Description:
FIELD OF THE INVENTION 
     The present invention relates to an atomization mechanism for cooling a bond head and a bonding apparatus comprising such atomization mechanism. 
     BACKGROUND OF THE INVENTION 
     One of the modules in a bonding machine for electronic devices, such as a die bonding machine, is the bond head. During a bonding process, an electronic device is first placed onto a collet of the bond head. The collet is then heated to about 350 degrees Celsius using a heater assembled in the bond head. Such heating melts the solder balls attached with the electronic device and while the solder balls are melted, the electronic device is urged against a bonding site, such as a substrate, with a predetermined force. As a result, the electronic device is bonded with the substrate via the melted solder balls. To strengthen this bond, the solder balls are cooled so that they can solidify and harden. It is beneficial to heat and cool the solder balls as quickly as possible so as to increase bond quality and productivity. 
     Conventional methods of increasing the heating rate include pulse heating, whereas conventional methods of increasing the cooling rate include actively cooling the bond head heater by blowing compressed gas or passing liquid through cooling channels inside the bond head. However, even with such active cooling of the bond head heater, the cooling rate remains unsatisfactory. 
     To further increase the cooling rate of the solder balls, US Patent Publication Number 2016/0116217A1 describes a bond head having a plurality of spray nozzles inside it. More specifically, the spray nozzles are positioned below the heater of the bond head. To cool the heater, a water spray is generated and is directed at the bottom surface of the heater via each of the spray nozzles. However, it is difficult to install the spray nozzles in bond heads which are small in size and which have small heaters (e.g. heaters which are less than 16 mm×16 mm in size). Therefore, the bond head has to be relatively large in order to accommodate the spray nozzles. Further, due to the tiny openings of the spray nozzles, the amount of water spray that can be generated and directed at the heater is limited. 
     SUMMARY OF THE INVENTION 
     The present invention aims to provide a new and useful atomization mechanism for cooling a bond head. 
     In general terms, the present invention proposes an atomization mechanism having an atomization module operative to form an atomized spray and a conduit configured to convey this atomized spray to the bond head to cool the bond head. 
     Specifically, a first aspect of the present invention is an atomization mechanism for cooling a bond head, the atomization mechanism comprising: an atomization module configured to receive gas and liquid from a gas supply and a liquid supply respectively to form an atomized spray; and a conduit configured to convey the atomized spray from the atomization module to a spray inlet located at the bond head to receive the atomized spray into the bond head. 
     Using an atomized spray to cool the bond head increases the rate of cooling the bond head. This in turn increases the productivity (as measured in units processed per hour) of the bonding machine. By having the atomization module (in which the atomized spray is formed) outside the bond head, the atomization module can be used with more compact bond heads with smaller heaters, and the overall bonding apparatus can be more compact. The flow rate of the atomized spray can also be more easily controlled. 
     The atomization mechanism may further comprise a liquid pressure regulator operative to adjust a pressure of the liquid supply to the atomization module. This allows the control of the liquid supply flow rate to the atomization module. 
     The atomization mechanism may further comprise a gas pressure regulator operative to adjust a pressure of the gas supply to the atomization module. Similarly, this allows the control of the gas supply flow rate to the atomization module. 
     The atomization mechanism may further comprise a gas measuring unit operative to measure one or both of a pressure and a flow rate of the gas supply to the atomization module. This provides feedback that can be used to adjust the gas flow to achieve a desired flow rate. 
     The atomization mechanism may further comprise valves which are configured to be selectively activated to control a flow of the gas supply and a flow of the liquid supply into the atomization module. This allows the initiation and stopping of the liquid spray formation in the atomization module. 
     A second aspect of the present invention is a bonding apparatus comprising: a bond head comprising: a holding element configured to hold an electronic device; a heater configured to heat the holding element; and a spray inlet located at the bond head and configured to receive an atomized spray into the bond head to cool the heater; and an atomization mechanism comprising: an atomization module configured to receive gas and liquid from a gas supply and a liquid supply respectively to form the atomized spray; and a conduit configured to convey the atomized spray from the atomization module to the spray inlet located at the bond head. 
     The bonding apparatus may further comprise a plurality of leakage sensors arranged to detect leakage of the liquid from one or both of the atomization mechanism and bond head. This allows early detection of liquid leakage around the bond head and the atomization mechanism, in turn allowing early rectification of any leakage to be conducted. In this way, the impact of the leakage on production can be reduced, and further potentially more serious damage of the atomization mechanism and bond head due to the leakage can be avoided. 
     The bonding apparatus may further comprise a plurality of humidity sensors arranged to determine a relative humidity around the bond head. This provides an additional feedback facilitating the early detection of liquid leakage around the bond head. 
     The bonding apparatus may further comprise a separating mechanism configured to receive the atomized spray from the bond head, the separating mechanism being operative to separate the atomized spray into liquid and gas respectively. This allows the atomized spray to cool down without the need for a radiator. Thus, problems associated with the radiator, such as having water droplets left in the chimney of the radiator and a high back pressure at an exhaust of the bond head can be avoided. 
     The separating mechanism may comprise a hollow body configured to cause the atomized spray to form a rotating spray flow. This achieves an efficient separation of the atomized spray into liquid and gas. The rotating spray flow may rotate in a helical pattern. 
     The separating mechanism may comprise a hollow body having a cylindrical portion coupled with a frusto-conical portion. Such a structure can be easily manufactured to cause the atomized spray to form the high speed rotating spray flow. 
     The bond head may further comprise a cooling channel through which the spray inlet is conveyed, the cooling channel being connected to the spray inlet and having a cooling portion in contact with the heater along a surface of the heater. Heat can thus be transferred from the surface of the heater in contact with the cooling portion to atomized spray passing through the cooling portion. In this way, the cooling rate of the heater is improved by directing the atomized spray over a greater surface area of the heater. 
     The cooling channel may further comprise an inclined inlet configured to direct the atomized spray into the cooling portion, the inclined inlet being inclined at an angle of between 30 to 60 degrees with respect to the cooling portion. Such inclination helps to increase the speed of flow of the atomized spray through the cooling portion by reducing the cross sectional area of the flow regime adjacent to (such as before and after) the cooling portion. This in turn increases the heat transfer coefficient between the heater and the atomized spray flowing through the cooling portion. Furthermore, by maximizing the speed of flow of the atomized spray, the chances of the spray droplets coming into contact with the heater increase. It can also further break down the water spray into small sizes and reduce the flow resistance (pressure drop) in the flow path of the atomized spray as it flows through the cooling channel. The inclination further allows the inclined inlet to hold liquid droplets remaining from a previous atomized spray flow by the force of surface tension, preventing liquid droplets from flowing through the cooling portion when the heater is heating the holding element or when no heating or cooling is to be performed. 
     The cooling channel may further comprise an inclined outlet configured to direct the atomized spray exiting the cooling portion, the inclined outlet being inclined at an angle of between 30 to 60 degrees with respect to the cooling portion. Similarly, this can increase the speed of flow of the atomized spray through the cooling portion, increasing the heat transfer coefficient between the heater and the atomized spray. It can also further break down the water spray into small sizes and reduce the flow resistance (pressure drop) in the flow path of the atomized spray as it flows through the cooling channel. Such inclination further allows the inclined outlet to hold liquid droplets remaining from a previous atomized spray flow by the force of surface tension. 
     The bonding apparatus may further comprise a heater control mechanism operative to control the atomization mechanism and a power supply to the heater based on a temperature of the heater. This allows the regulation of the heater&#39;s temperature. The heater control mechanism may be operative to initiate the formation of the atomized spray in the atomization module upon detecting a need to cool the heater. The heater control mechanism may be operative to adjust the power supply to change a heating rate of the heater based on the temperature of the heater. 
     A third aspect of the present invention is a bonding apparatus comprising: a bond head comprising: a holding element configured to hold an electronic device; a heater configured to heat the holding element; and an insulating element configured to reduce transmission of heat away from the heater; and an atomization mechanism configured to receive gas and liquid from a gas supply and a liquid supply respectively to form an atomized spray; wherein the atomization mechanism is external to the bond head and is operative to convey the atomized spray to the bond head for cooling the heater. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       An embodiment of the invention will now be illustrated for the sake of example only with reference to the following drawings, in which: 
         FIG. 1  is a schematic representation of a bonding apparatus according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of a bond head of the bonding apparatus of  FIG. 1 ; 
         FIG. 3( a )  is a partial sectional view of the bond head of  FIG. 2  and  FIG. 3( b )  is a partial sectional view of a top portion of the bond head; 
         FIG. 4  is a perspective view of a heater plate of the bonding apparatus of  FIG. 1 ; 
         FIG. 5  is a sectional view of an atomization module of the bonding apparatus of  FIG. 1 ; 
         FIG. 6  is a sectional view of a cyclone separator of the bonding apparatus of  FIG. 1 ; and 
         FIG. 7  is a schematic diagram illustrating an interaction of a heater control mechanism with an atomization mechanism and the bond head of the bonding apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic representation of a bonding apparatus  100  according to an embodiment of the present invention. 
     The bonding apparatus  100  comprises a bond head  102  having a heater comprised in a heater plate (not shown in  FIG. 1 ), an atomization mechanism  104  and a heater control mechanism  106 . The heater control mechanism  106  is configured to regulate a temperature of the heater plate by controlling the heating and cooling of the heater plate. The atomization mechanism  104  is configured to provide an atomized spray in the form of a liquid spray (which is a mixture of gas and liquid) to the bond head  102  to cool the heater plate. 
     A first and second plurality of leakage sensors  108 ,  110  are provided near the bond head  102  and the atomization mechanism  104  respectively and are arranged to detect leakage of liquid from the bond head  102  and the atomization mechanism  104 . A plurality of humidity sensors  112  is also provided in a vicinity of the bond head  102  to determine a relative humidity around the bond head  102 . The heater control mechanism  106  is connected to the sensors  108 ,  110 ,  112  via signaling cables  136 . The sensors  108 ,  110 ,  112  are configured to send signals to the heater control mechanism  106  via these signaling cables  136  to indicate the amount of liquid leakage from the bond head  102  and the atomization mechanism  104 , and the relative humidity around the bond head  102 . If the amount of leakage is too large or if the relative humidity around the bond head  102  is too high, it is determined that the bonding apparatus  100  is faulty. In this case, the bonding apparatus  100  is shut down for detailed checking and rectification. 
     The bonding apparatus  100  also comprises a separating mechanism in the form of a cyclone separator  114  connected to the bond head  102 . The cyclone separator  114  is configured to receive the liquid spray from the bond head  102  and is further configured to separate the liquid spray into liquid and gas. 
     As shown in  FIG. 1 , the atomization mechanism  104  includes a liquid supply chain connected to a liquid supply and a gas supply chain connected to a compressed gas supply. The liquid supply chain and the gas supply chain are configured to provide liquid and compressed gas respectively to an atomization module  126  external to the bond head  102 . 
     The liquid supply chain includes a liquid filter  116 , a liquid pressure regulator  118 , a liquid measuring unit having a liquid pressure gauge  120 , a liquid flowmeter  122 , and a liquid solenoid valve  124 . The liquid filter  116  is connected to the liquid supply, and is configured to receive liquid from the liquid supply and to remove debris from the received liquid. The liquid pressure regulator  118  is configured to receive the filtered liquid from the liquid filter  116  and to adjust the pressure of the liquid supply to the atomization module  126 . The liquid solenoid valve  124  is configured to control the flow of the liquid supply into the atomization module  126 . In particular, the activation of the liquid solenoid valve  124  allows flow of the liquid into the atomization module  126  and the deactivation of the liquid solenoid valve  124  prevents flow of the liquid into the atomization module  126 . The liquid pressure gauge  120  and liquid flowmeter  122  are operative to cooperate to determine the pressure and flow rate of the liquid supply to the atomization module  126  when the liquid solenoid valve  124  is activated. 
     Similarly, the gas supply chain comprises a gas pressure regulator  128 , a gas measuring unit including a gas pressure gauge  130  and a gas flowmeter  132 , and a gas solenoid valve  134 . The gas pressure regulator  128  is connected to the gas supply and is configured to adjust the pressure of the gas supply to the atomization module  126 . Similar to the liquid solenoid valve  124 , the gas solenoid valve  134  serves to control the flow of the gas supply into the atomization module  126 . Specifically, when the gas solenoid valve  134  is activated, flow of gas into the atomization module  126  is enabled. On the other hand, when the gas solenoid valve  134  is deactivated, flow of gas into the atomization module  126  is prevented. The gas pressure gauge  130  and gas flowmeter  132  are configured to determine the pressure and flow rate of the gas supply to the atomization module  126  when the gas solenoid valve  134  is activated. 
     Signaling cables  138  connect the gas and liquid solenoid valves  124 ,  134 , flowmeters  122 ,  132  and pressure gauges  120 ,  130  to the heater control mechanism  106 . The heater control mechanism  106  is configured to send control signals to these components to control them and to adjust their parameters. 
       FIG. 2  is a perspective view of the bond head  102 . As shown in  FIG. 2 , the bond head  102  comprises the heater plate  202  at one end. A holding element in the form of a collet (not shown in  FIG. 2 ) is connected to a top surface of the heater plate  202  and is configured to hold an electronic device, such as a semiconductor die. The heater plate  202  is configured to heat the holding element, thereby heating the electronic device. 
     At an opposite end from the heater plate  202 , the bond head  102  comprises a base  210  that is attachable to a bond head column of a die bonding machine. The base  210  comprises a spray inlet  212  configured to receive the liquid spray from the atomization mechanism  104  into the bond head  102  to cool the heater plate  202 . Two exhaust outlets  214  are provided on the base  210  of the bond head  102 . The exhaust outlets  214  are configured to allow the liquid spray to exit the bond head  102 . The exhaust outlets  214  are connected to the cyclone separator  114 , so that the exiting liquid spray is fed into the cyclone separator  114 . 
     The heater plate  202  is locked to an insulation element in the form of an insulation block  204  via a clamping plate  208  secured by screws  206 . The insulation block  204  is positioned below the heater plate  202  and is configured to reduce transmission of heat away from the heater plate  202  (particularly, transmission of heat from the heater plate  202  to the base  210 ), so as to increase the heating efficiency. Sealing ceramic glue is applied to gaps between the heater plate  202  and the insulation block  204  to seal these gaps. The bond head  102  also comprises temperature sensors attached to the heater plate  202  to determine the temperature of the heater plate  202 . These temperature sensors are configured to send temperature feedback to the heater control mechanism  106 . 
       FIG. 3( a )  is a partial sectional view of the bond head  102 . As shown in  FIG. 3( a ) , the spray inlet  212  leads to a cooling channel having an input portion  302 , a cooling portion  304  and an output portion  306 . The cooling channel further comprises an inclined inlet  308  extending from the input portion  302  to the cooling portion  304 , and an inclined outlet  310  extending from the cooling portion  304  to the output portion  306 . The input and output portions  302 ,  306  extend through the base  210  and insulation block  204 , whereas the cooling portion  304  extends along a surface of the heater plate  202 , allowing liquid spray passing through the cooling portion  304  to come into contact with the heater plate  202  along this surface. 
       FIG. 3( b )  is a partial sectional view of a top portion of the bond head  102 . As shown in  FIG. 3( b ) , the inclined inlet  308  and inclined outlet  310  are inclined with respect to the cooling portion  304  at an angle of about 30 degrees. Such inclination helps to increase the speed of flow of the liquid spray through the cooling portion  304  by reducing the cross sectional area of the flow regime before and after the cooling portion  304 . This in turn increases the heat transfer coefficient between the heater plate  202  and the liquid spray flowing through the cooling portion  304 . Furthermore, by maximizing the speed of flow of the liquid spray, the chances of the liquid droplets coming into contact with the heater plate  202  increase, and the pressure drop (flow resistance) of the liquid spray as it enters the cooling portion  304  decreases. The inclination also allows the inclined inlet  308  and inclined outlet  310  to hold liquid droplets remaining from a previous liquid spray flow by the force of surface tension. This prevents liquid droplets from flowing through the cooling portion  304  when the heater plate  202  is heating the collet or during an idle state when no heating or cooling is to be conducted. 
     To enhance a cooling efficiency of the heater plate  202 , the heater plate  202  further includes a plurality of fins (not shown in  FIG. 3( a )  or  FIG. 3( b ) ) and is coated with a cooling layer in the form of a TiO 2  layer  312  on its bottom surface to reduce a film boiling effect. 
       FIG. 4  is a perspective view of the heater plate  202 , showing the fins  402  of the heater plate  202 . The fins  402  provide an increased area for heat transfer between the heater plate  202  and the liquid spray through the cooling portion  304 . With the fins  402 , the chances of the liquid droplets through the cooling portion  304  coming into contact with the heater plate  202  can also be increased. 
       FIG. 5  is a sectional view of the atomization module  126 . The atomization module  126  is configured to allow the gas and liquid to mix to form the liquid spray. As shown in  FIG. 5 , the atomization module  126  comprises a mixing tube  502  and a conveying tube  504 , and a T-joint  506  connecting the mixing and conveying tubes  502 ,  504 . A diameter of the mixing tube  502  is narrower than a diameter of the conveying tube  504 . The atomization module  126  also includes a liquid inlet  508  with one end connected to the liquid supply chain and the other end connected to the mixing tube  502 . One end of the mixing tube  502  is an open end and serves as a first compressed gas inlet  510 . The other end of the mixing tube  502  is connected to the T-joint  506 , which is in turn connected to the conveying tube  504 . The conveying tube  504  has two open ends, one serving as a second compressed gas inlet  512  and the other serving as a liquid spray outlet  514 . The gas inlets  510 ,  512  are independently connected to the gas supply chain. The liquid spray outlet  514  is connected to a conduit, such as a tube. The conduit is in turn connected to the spray inlet  212  of the bond head  102  and is configured to convey the liquid spray  520  from the atomization module  126  to the spray inlet  212 . 
       FIG. 6  is a sectional view of the cyclone separator  114 . As mentioned above, the cyclone separator  114  is configured to receive the liquid spray from the bond head  102  and is further configured to separate the liquid spray into liquid and gas. 
     The cyclone separator  114  comprises a hollow body  604  designed to cause the liquid spray entering the cyclone separator  114  to form a high speed rotating spray flow. To elaborate, the hollow body  604  has a cylindrical portion  604   a  coupled with a frusto-conical portion  604   b . A hot spray inlet  602  is provided on the surface of the cylindrical portion  604   a  to receive the liquid spray from the bond head  102 . The cylindrical portion  604   a  includes a covered end through which a cylindrical gas outlet  606  extends to allow exit of the gas separated from the liquid spray. Opposite the covered end, the cylindrical portion  604   a  includes an open end coupled with a first open end of the frusto-conical portion  604   b . These open ends of the cylindrical and frusto-conical portions  604   a ,  604   b  have equal cross-sectional areas. The frusto-conical portion  604   b  also has a second open end opposite the first open end. This second open end serves as a liquid outlet  606  for liquid that has been separated from the liquid spray. The frusto-conical portion  604   b  tapers from the first open end towards the second open end. 
       FIG. 7  shows the interaction of the heater control mechanism  106  with the atomization mechanism  104  and the bond head  102 . For illustration purposes, only the liquid solenoid valve  124 , gas solenoid valve  134  and atomization module  126  of the atomization mechanism  104  are shown in  FIG. 7 . 
     As shown in  FIG. 7 , the heater control mechanism  106  is configured to receive temperature feedback from the temperature sensors of the bond head  102 , and is further configured to control a power supply to the heater plate  202  and the atomization mechanism  104  based on the temperature feedback. More specifically, the heater control mechanism  106  is operative to adjust the power supply to change the heating rate of the heater plate  202  depending on whether the heater plate  202  needs to be heated or cooled. The heater control mechanism  106  is also operative to initiate the formation of the liquid spray in the atomization mechanism  104  upon detecting a need to cool the heater plate  202  and to stop directing the liquid spray to the bond head  102  upon detecting a need to heat up the heater plate  202 . The control of the atomization mechanism  104  by the heater control mechanism  106  is performed via control signals configured to activate and deactivate the liquid and gas solenoid valves  124 ,  134 . The heater control mechanism  126  is also operative to adjust the operating parameters (for example, the operating time) of the liquid and gas solenoid valves  124 ,  134 . Such adjustment allows control and variation of the flow rate of the liquid spray into the bond head  102  (which in turn affects the rate of cooling the heater plate  202 ). It also allows the adjustment of the relative proportions of the liquid and gas in the liquid spray. 
     In use, an electronic device attached with solder balls is picked up and held on the collet of the bond head  102 . Next, the power supply to the heater plate  202  is turned on. As the heater plate  202  is being heated up, the heater control mechanism  106  sends control signals to the liquid solenoid valve  124  to activate it. The activation of the liquid solenoid valve  124  introduces liquid into the atomization module  126 , specifically, into the mixing tube  502  via the liquid inlet  508 . Note however that the gas solenoid valve  134  remains deactivated so that no liquid spray is directed to the bond head  102  at this time. 
     The heater plate  202  is heated up to a first target temperature of 350 degrees Celsius and is maintained at this first target temperature for a predetermined period of time. This melts the solder balls that are attached on the electronic device. While the solder balls are melted, the electronic device is urged against a bonding site on a substrate with a predetermined force, with the solder balls abutting the substrate. As a result, the electronic device is bonded to the substrate via the solder balls. 
     After a predetermined period of time, the heater plate  202  is cooled to a second target temperature and is maintained at this second target temperature before another electronic device is picked up and held on the collet of the bond head  102  (after which, the heater plate  202  is heated up to the first target temperature again). The cooling of the heater plate  202  cools the electronic device together with the substrate. This solidifies and hardens the solder ball joints between the substrate and the electronic device, strengthening the bond between them. Note that the second target temperature is above an evaporation temperature of the liquid to prevent liquid droplets from being left in the cooling portion  304  of the cooling channel in the bond head  102 . 
     The heater plate  202  is heated up or cooled to, and maintained at a desired temperature (either the first or second target temperature) using the heater control mechanism  106 . In particular, the temperature sensors of the bond head  102  sense the temperature of the heater plate  202  and provide temperature feedback to the heater control mechanism  106 . If the temperature feedback indicates that the temperature of the heater plate  202  is above the desired temperature, the heater control mechanism  106  adjusts the power supply to reduce the heating rate of the heater plate  202  (or maintains the power supply at the same level if the heating rate is already at the lowest heating rate). The heater control mechanism also starts or continues a cooling process (as elaborated below) to cool the heater plate  202 . If on the other hand, the temperature feedback indicates that the temperature of the heater plate  202  is at or below the desired temperature, the heater control mechanism  106  adjusts the power supply to increase the heating rate of the heater plate  202  (or maintains the power supply at the same level if the heating rate is already at the highest heating rate). If the cooling process is being carried out, the heater control mechanism  106  also stops this cooling process. 
     The cooling process is elaborated below. 
     At the start of the cooling process, the heater control mechanism  106  sends control signals to the gas solenoid valve  134  to activate it. The activation of the gas solenoid valve  134  introduces a high-speed flow of gas simultaneously into the mixing tube  502  of the atomization module  126  via the first compressed gas inlet  510 , and the conveying tube  504  of the atomization module  126  via the second compressed gas inlet  512 . This high-speed flow of gas blows the liquid previously introduced into the mixing tube  502 . Initially, a wavy surface liquid film  516  (see  FIG. 5 ) is formed. As the gas continues to flow into the mixing tube  502 , a first gas tearing action caused by the high speed gas flow disintegrates the liquid film  516  into liquid droplets  518 . The liquid droplets  518  then flow through the T-joint  506  into the conveying tube  504  of the atomization module  126 . In the conveying tube  504 , the liquid droplets  518  interact with the gas flow introduced via the second compressed gas inlet  512  to form the liquid spray  520 . In particular, the continuous high-speed gas flow into the conveying tube  504  causes a second gas tearing action which converts the liquid droplets  518  into the liquid spray  520 . The liquid spray  520  then flows out of the atomization module  126  via the liquid spray outlet  514  into the conduit. The conduit connected to the atomization module  126  then conveys the liquid spray from the atomization module  126  to the spray inlet  212  of the bond head  102 . 
     The liquid spray enters the bond head  102  via the spray inlet  212 . Inside the bond head  102 , the liquid spray flows through the cooling channel to which the spray inlet  212  leads. In particular, the input portion  302  of the cooling channel directs the liquid spray from the spray inlet  212  to the inclined inlet  308 . The inclined inlet  308  then directs the liquid spray to the cooling portion  304 . The cooling portion  304  allows the liquid spray through it and since it is in contact with the bottom surface of the heater plate  202 , heat is transferred from the heater plate  202  to the liquid spray. This cools the heater plate  202  and heats up the liquid spray. The inclined outlet  310  then directs the hot liquid spray exiting the cooling portion  304  to the output portion  306  which in turn directs the hot liquid spray to one of the exhaust outlets  214 . 
     The hot liquid spray exits the bond head  102  via the exhaust outlet  214  and flows into the hot spray inlet  602  of the cyclone separator  114 . This leads the hot liquid spray into the cylindrical portion  604   a  of the cyclone separator&#39;s hollow body  604 . The cyclone separator  114  is arranged such that the hot liquid spray flows downwards through the cylindrical portion  604   a  and then through the frusto-conical portion  604   b , cooling down as it flows. This causes the liquid spray to flow in a helical pattern in the frusto-conical portion  604   b , forming a high speed rotating spray flow in this portion  604   b . This in turn separates the liquid from the gas in the liquid spray. In particular, liquid in the rotating spray flow is unable to follow the flow path and thus, strikes the walls of the frusto-conical portion  604   b  and falls to the bottom of the frusto-conical portion  604   b  where the liquid outlet  606  is. The liquid then flows through the liquid outlet  606  and is collected at the liquid supply so that the liquid can be reused. The rest of the liquid spray comprises moisture gas which flows in a straight line from the frusto-conical portion  604   b  to the cylindrical portion  604   a  and out of the cyclone separator  114  via the moisture outlet  608 . 
     To stop the cooling process, the heater control mechanism  106  sends control signals to the liquid and gas solenoid valves  124 ,  134  to deactivate these valves  124 ,  134 . This prevents the liquid and gas from entering the atomization module  126 , in turn stopping the formation of the liquid spray. As a result, flow of the liquid spray into the bond head  102  is stopped. 
     Various modifications will be apparent to those skilled in the art. 
     For example, the angle at which the inclined inlet  308  is inclined with respect to the cooling portion  304  need not be 30 degrees and may range from 30 to 60 degrees (inclusive of 30 and 60 degrees). Similarly, the angle at which the inclined outlet  310  is inclined with respect to the cooling portion  304  need not be 30 degrees and may also range from 30 to 60 degrees (inclusive of 30 and 60 degrees). Further, the inclined inlet  308  and the inclined outlet  310  may be inclined with respect to the cooling portion  304  at different angles. 
     Also, the conduit need not be in the form of a tube. The conduit may be in any other form as long as it can convey the liquid spray from the atomization module  126  to the spray inlet  212  of the bond head  102  at an acceptable rate. 
     In addition, instead of the TiO 2  layer  312 , the cooling layer coating the bottom surface of the heater plate  202  may be in the form of a different hydrophilic layer such as a SiO 2  layer. Further, the liquid may be in the form of distilled water or any other cooling agent suitable for cooling the heater plate  202 . Similarly, the gas may be in any form suitable for atomizing the liquid to form the liquid spray. 
     The number of spray inlets  212  and exhaust outlets  214  may also vary from those in the bond head  102 . There may also be more than one cooling channel to further increase the cooling efficiency. 
     In addition, although in the embodiment described above, the liquid and gas are introduced into the atomization module  126  at different times to form the liquid spray (in particular, the liquid is introduced while the heater plate  202  is being heated up, whereas the gas is introduced only upon detecting a need to cool the heater plate  202 ), it is possible to introduce the liquid and gas simultaneously into the atomization module  126  upon detecting the need to cool the heater plate  202 . 
     Further, to cool the heater plate  202 , it is also not necessary to both adjust the power supply to the heater plate  202  and perform the cooling process. Instead, it may be sufficient to simply perform the cooling process.