Patent Publication Number: US-6214718-B1

Title: Semiconductor assembling method and apparatus

Description:
This is a divisional application of Ser. No. 08/689,912, filed Aug. 16, 1996, now U.S. Pat. No. 5,934,996. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor assembling method and apparatus for joining semiconductor chips with lead frames and the like in semiconductor fabrication processes. 
     Semiconductor chips are connected with external electrodes, such as lead frames, by means of a wire made of gold, aluminium or the like and by using a wire bonder. This wire is connected with the semiconductor chips or external electrodes by heat or ultrasonic waves or by both. 
     Among the wire bonders, in each of those using the bonding process so called ball bonding, a ball is formed at the tip of the wire by electric discharge or other heating means. The junction conditions for this process include the temperature of the stage at which semiconductor chips and external electrodes are heated, the pressure with which the wire is pressed as well as its time, and the oscillation output of ultrasonic waves as well as its time. 
     These conditions are previously stored as data in the wire bonder. These data are given as fixed data in all, or fixed data for each wire. 
     In the case where the wire bonder performs bonding processes continuously for a plurality of wires, the pressurizing tool receives heat from the semiconductor chip heater, resulting in a temperature rise. The ball also comes to a high temperature because the bonding process is carried out immediately after the formation of the ball. 
     However, when the interval from one bonding process to another is prolonged, for example, during the transfer of semiconductor chips or at a restart after a halt, the temperature of the pressurizing tool or the ball would, lower. This poses an issue that the alloying of the wire and the semiconductor chip is suppressed such that a deterioration in the bondability may occur. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is therefore to provide semiconductor assembling method and apparatus which allow the junction to be accomplished without being affected by temperature decreases of the pressurizing tool or the ball even if the interval to the subsequent bonding process is prolonged. 
     In accomplishing these and other objects, according to a first aspect of the present invention, there is provided a semiconductor assembling method for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling method comprising steps of: 
     measuring a time elapsing from a last bonding process to a subsequent bonding process; and 
     changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured time. 
     According to a second aspect of the present invention, there is provided a semiconductor assembling method for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling method comprising steps of: 
     measuring a temperature of the pressurizing tool; and 
     changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured temperature. 
     According to a third aspect of the present invention, there is provided a semiconductor assembling method for joining a bonding wire with a bonding object by forming a ball at a tip of the bonding wire with energy applied to the bonding wire, by pressing the bonding wire against the bonding object with a bonding pressurizing tool, and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling method comprising steps of: 
     measuring a temperature of the tip of the bonding wire; and 
     changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured temperature. 
     According to a fourth aspect of the present invention, there is provided a semiconductor assembling method for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling method comprising steps of: 
     measuring a time elapsing from when a ball is formed at a tip of the bonding wire with energy applied to the bonding wire until when the bonding wire is pressed against the bonding object with the bonding pressurizing tool; and 
     changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured time. 
     According to a fifth aspect of the present invention, there is provided a semiconductor assembling apparatus for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling apparatus comprising: 
     a bonding-interval measuring means for measuring a time elapsing from a last bonding process to a subsequent bonding process; and 
     a junction condition changing means for changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured time. 
     According to a sixth aspect of the present invention, there is provided a semiconductor assembling apparatus for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling apparatus comprising: 
     a pressurizing tool temperature measuring means for detecting a temperature of the pressurizing tool; and 
     a junction condition changing means for changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured temperature of the pressurizing tool. 
     According to a seventh aspect of the present invention, there is a semiconductor assembling apparatus for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling apparatus comprising: 
     a ball forming means for forming a ball at a tip of the bonding wire with energy applied to the bonding wire; 
     a time measuring means for measuring a time elapsing from the formation of the ball at the tip of the bonding wire by the ball forming means until the subsequent bonding process; and 
     a junction condition changing means for changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured time. 
     According to an eighth aspect of the present invention, there is provided a semiconductor assembling apparatus for joining a bonding wire with a bonding object by pressing the bonding wire against the bonding object with a bonding pressurizing tool and by effecting at least one junction process of thermal junction or ultrasonic junction, 
     the semiconductor assembling apparatus comprising: 
     a ball forming means for forming a ball at a tip of the bonding wire with energy applied to the bonding wire; 
     a temperature measuring means for measuring a temperature of the tip of the bonding wire; and 
     a junction condition changing means for changing at least one junction condition of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time for the subsequent bonding process, based on the measured temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is an arrangement view of an apparatus for joining semiconductor chips according to a first embodiment of the present invention; 
     FIG. 2 is an arrangement view of an apparatus for joining semiconductor chips according to a second embodiment of the present invention; 
     FIG. 3 is an arrangement view of an apparatus for joining semiconductor chips according to a third embodiment of the present invention; and 
     FIG. 4 is an arrangement view of an apparatus for joining semiconductor chips according to a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. 
     Embodiments of the present invention are described hereinbelow with reference to FIGS. 1 to  4 . 
     FIG. 1 shows a first embodiment of the invention. 
     The first embodiment is an example in which, based on measurement results obtained from a bonding-interval measuring means which is set on a wire bonding device of the thermosonic-junction ball bonding or wedge bonding method and which measures the time elapsing from the last bonding process to the subsequent bonding process, the assembling process is carried out by changing part or all of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time. 
     The wire bonding device feeds a bonding wire  2  from a wire feeder  1  to a bonding pressurizing tool  3  by an optimum length by an unshown drive method, and presses the bonding pressurizing tool  3  against a bonding object  6  by a pressurizer  4 . The object  6  is an external lead of a semiconductor chip or lead frame. Designated by reference numeral  5  is a heater for heating the bonding object  6 . The pressurizer  4  is implemented by an AC servo motor, linear motor, air cylinder or the like. The pressurizing tool  3  is so arranged that ultrasonic waves generated from an ultrasonic oscillator  7  are transferred to the wire  2  of the junction part. 
     A main controller  9  for controlling the whole bonding process reads the data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time from a data storage  10 , and outputs them to a calculating means  11 . 
     The calculating means  11  is so arranged as to change the data according to measured time T obtained from an interval measuring means  12  that measures the time elapsing from the last bonding process to the subsequent bonding process and to send commands to a pressurizing force and time control means  13  and an ultrasonic oscillation output and time control means  8 . The calculating means  11  is also arranged so as to strengthen the junction conditions when the measured time T has become a prolonged one which is longer than an allowable interval time between the continuously bonding processes. For example, when an ordinary interval time between the continuously bonding processes is 0.1 seconds and the measured time T is within an allowable interval time of 10 seconds, the junction condition is not changed because the measure time T is within the allowable area. When the measured time T is longer than the allowable interval time of 10 seconds, the junction condition(s) is changed. Strengthening the junction conditions means increasing the pressurizing force, or prolonging the pressurizing time, or increasing the ultrasonic oscillation output, or prolonging the ultrasonic oscillation time. In order to avoid any damage to the object  6  by excessively increasing the pressurizing force, it is preferable that the pressurizing force is increased to a small extent and the ultrasonic oscillation output is increased. The strengthening of the junction conditions also merely means that all junction conditions are increased. That is, the strengthening of the junction conditions also means that the pressurizing time is decreased while the pressurizing force is increased so as to increase junction energy, and that the ultrasonic oscillation time is decreased while the ultrasonic oscillation output is increased so as to increase junction energy. 
     The pressurizing force and time control means  13  controls the pressurizer  4  in compliance with the command given from the calculating means  11 . The ultrasonic oscillation output and time control means  8  controls the ultrasonic oscillator  7  in compliance with the command given from the calculating means  11 . 
     Explaining according to the junction procedure, the main controller  9  makes the bonding-interval measuring means  12  start at the time of bonding pressurization. In the subsequent bonding process, the calculating means  11  receives the measured time T from the bonding-interval measuring means  12 , receives bonding condition data read from the data storage  10  via the main controller  9 , performs predetermined calculation, and issues commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculation as one example is performed by the calculation means  11  as follows: A table showing relationship between the measured time T and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time is stored in the data storage  10 . Then, based on the measured time T, the to-be-strengthened data and the to-be-increased value thereof for strengthening are read from the table by the calculating means  11  and are sent as the commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8  by the calculating means  11 . The calculation can be performed by using an equation showing relationship between the measured time T and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time which is stored in the data storage  10 . 
     The bonding wire  2  is pressurized against the bonding object  6  by the pressurizing tool  3 , and ultrasonic oscillation is further effected, by which the junction of the bonding wire  2  and the bonding object  6  is completed. 
     As a result, since the junction conditions can be strengthened by detecting bonding intervals, any deterioration in the bondability can be prevented. 
     In addition, it is apparent that the ultrasonic oscillator  7  and the ultrasonic oscillation output and time control means  8  are unnecessary when a thermal junction method alone is used as the junction method, and that the heater  5  is unnecessary when an ultrasonic junction alone is used. 
     FIG. 2 shows a second embodiment of the present invention. 
     The second embodiment is an example in which the assembling process is carried out by changing part or all of the pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time based on a result obtained from a pressurizing tool temperature measuring means. 
     Reference numeral  14  denotes a pressurizing tool temperature measuring sensor for measuring the temperature of the pressurizing tool  3 . The pressurizing tool temperature measuring sensor  14  is exemplified by a thermocouple or non-contact heat sensor. Designated by numeral  15  is a pressurizing tool temperature measuring means for measuring the temperature of the pressurizing tool based on an output of the pressurizing tool temperature measuring sensor  14 . The other components including the wire feeder  1 , the bonding wire  2 , the pressurizing tool  3 , the pressurizer  4 , the heater  5 , the bonding object  6 , the ultrasonic oscillator  7 , the ultrasonic oscillation output and time control means  8 , the main controller  9 , and the data storage  10  are the same as in the first embodiment. 
     The calculating means  11  of this second embodiment is so connected as to change the data based on the measured temperature obtained from the pressurizing tool temperature measuring means  15 , and to send commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculating means  11  strengthens the junction conditions when the measured temperature has become a lowered one which is lower than an allowable temperature at the bonding process. For example, in a case where an ordinary temperature at the bonding process is 100° C., when the measured temperature is lower than 100° C. and equal to or higher than an allowable temperature of 50° C., the junction condition is not changed because the measure temperature is within the allowable area. When the measured temperature is lower than the allowable temperature of 50° C., the junction condition(s) is changed. 
     During the bonding process, the calculating means  11  receives the measured temperature from the pressurizing tool temperature measuring means  15 , receives bonding condition data from the data storage  10 , performs predetermined calculation, and issues commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculation as one example is performed by the calculation means  11  as follows: A table showing relationship between the measured temperature and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time is stored in the data storage  10 . Then, based on the measured temperature, the to-be-strengthened data and the to-be-increased value thereof for strengthening are read from the table by the calculating means  11  and are sent as the commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8  by the calculating means  11 . The calculation can be performed by using an equation showing relationship between the measured temperature and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time which is stored in the data storage  10 . 
     The bonding wire  2  is pressurized against the bonding object  6  by the pressurizing tool  3 , and ultrasonic oscillation is further effected, by which the junction of the bonding wire  2  and the bonding object  6  is completed. 
     As a result, since the junction conditions can be strengthened by detecting the temperature of the pressurizing tool, any deterioration in the bondability can be prevented. 
     FIG. 3 shows a third embodiment of the present invention. 
     The third embodiment is an example in which the assembling process is carried out by changing part or all of the pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time based on a result obtained from a time measuring means that measures the time elapsing after the formation of a ball until the subsequent bonding process. 
     Referring to FIG. 3, reference numeral  16  denotes an energy generator that imparts energy to the tip of the wire  2  so that a ball  17  is formed at the tip of the wire  2  by a ball forming means  117 . The energy generator  16  is exemplified by a high-voltage discharge device, as an example. 
     The calculating means  11  is so arranged as to change the data based on the measured time obtained from a time measuring means  18  that measures the time after the formation of the ball  17  until the subsequent bonding process, and to send commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculating means  11  strengthens the junction conditions when the measured time has become a prolonged one which is longer than an allowable interval time after the formation of the ball  17  until the subsequent bonding process. For example, when an ordinary interval time is 0.1 seconds and the measured time is within an allowable interval time of 10 seconds, the junction condition is not changed because the measure time is within the allowable area. When the measured time is longer than the allowable interval time of 10 seconds, the junction condition(s) is changed. The other components including the wire feeder  1 , the bonding wire  2 , the bonding pressurizing tool  3 , the pressurizer  4 , the heater  5 , the bonding object  6 , the ultrasonic oscillator  7 , the ultrasonic oscillation output and time control means  8 , the main controller  9 , and the data storage  10  are the same as in the first embodiment. 
     During the bonding process, the calculating means  11  receives the measured time from the time measuring means  18 , receives bonding condition data from the data storage  10 , performs predetermined calculation, and issues commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculation as one example is performed by the calculation means  11  as follows: A table showing relationship between the measured time after the formation of the ball  17  until the subsequent bonding process and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time is stored in the data storage  10 . Then, based on the measured time, the to-be-strengthened data and the to-be-increased value thereof for strengthening are read from the table by the calculating means  11  and are sent as the commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8  by the calculating means  11 . The calculation can be performed by using an equation showing relationship between the measured time and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time which is stored in the data storage  10 . 
     The bonding wire  2  is pressurized against the bonding object  6  by the pressurizing tool  3 , and ultrasonic oscillation is further effected, by which the junction of the bonding wire  2  and the bonding object  6  is completed. 
     As a result, since the junction conditions can be strengthened by detecting the time after the formation of the ball, any deterioration in the bondability can be prevented. 
     FIG. 4 shows a fourth embodiment of the present invention. 
     The fourth embodiment is an example in which the assembling process is carried out by changing part or all of the pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time based on a result obtained from a ball temperature measuring means. 
     Reference numeral  19  denotes a ball temperature measuring sensor, which is exemplified by a non-contact heat sensor, as an example. Designated by numeral  20  is a ball temperature measuring means for measuring the temperature of the ball  17  based on an output of the ball temperature measuring sensor  19 . The other components including the wire feeder  1 , the bonding wire  2 , the bonding pressurizing tool  3 , the pressurizer  4 , the heater  5 , the bonding object  6 , the ultrasonic oscillator  7 , the ultrasonic oscillation output and time control means  8 , the main controller  9 , and the data storage  10  are the same as in the first embodiment. 
     The calculating means  11  is so arranged as to change the data based on the measured temperature obtained from the ball temperature measuring means  20  that measures the temperature of the ball  17  formed by the ball forming means  117  and to send commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculating means  11  strengthens the junction conditions when the measured temperature has become a lowered one which is lower than an allowable ball temperature at the ball bonding process. For example, in a case where an ordinary ball temperature at the ball bonding process is 100° C., when the measured temperature is lower than 100° C. and equal to or higher than an allowable ball temperature of 50° C., the junction condition is not changed because the measured temperature is within an allowable area. When the measured temperature is lower than the allowable ball temperature of 50° C., the junction condition(s) is changed. 
     During the bonding process, the calculating means  11  receives the measured temperature from the ball temperature measuring means  20 , receives bonding condition data from the data storage  10 , performs predetermined calculation, and issues commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8 . The calculation as one example is performed by the calculation means  11  as follows: A table showing relationship between the measured ball temperature and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time is stored in the data storage  10 . Then, based on the measured ball temperature, the to-be-strengthened data and the to-be-increased value thereof for strengthening are read from the table by the calculating means  11  and are sent as the commands to the pressurizing force and time control means  13  and the ultrasonic oscillation output and time control means  8  by the calculating means  11 . The calculation can be performed by using an equation showing relationship between the measured temperature and the to-be-strengthened data of pressurizing force, pressurizing time, ultrasonic oscillation output, and ultrasonic oscillation time which is stored in the data storage  10 . 
     The bonding wire  2  is pressurized against the bonding object  6  by the pressurizing tool  3 , and ultrasonic oscillation is further effected, by which the junction of the bonding wire  2  and the bonding object  6  is completed. 
     As a result, since the junction conditions can be strengthened by detecting any decrease in the ball temperature, any deterioration in the bondability can be prevented. 
     In addition, even if the change of the junction conditions is made on only any one of the pressurizing time, pressurizing force, ultrasonic oscillation output, and ultrasonic oscillation time, it is possible to improve the bondability. Therefore, without the need of necessarily storing all the data by the data storage  10 , the bonding method and bonding apparatus may be implemented with some of the data fixed. 
     Although the apparatuses according to the first and second embodiments have no ball forming means  117  shown in FIGS. 3 and 4, each of the apparatuses can have such a ball forming means  117  shown in FIGS. 3 and 4 for performing the similar ball bonding process. 
     The allowable times and temperatures described in the first through fourth embodiments can be set based on various kinds of requirements at the junction processes. 
     As described above, according to the present invention, even if the interval from one bonding process to another is prolonged, for example, during the transfer process of semiconductor chips or at a restart after a halt, the junction of wire and object can be accomplished without being affected by any decrease in the temperature of the pressurizing tool or the ball. Thus, the bondability will never be deteriorated, advantageously. 
     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.