JP5930563B2 - Mounting method and mounting apparatus - Google Patents

Description

  The present invention relates to a mounting method and a mounting apparatus for thermocompression-bonding a flip chip with pillar bumps, on which solder is formed at the tip of a columnar pillar provided on the flip chip, to a substrate.

  In recent years, due to the demand for high density mounting, solder bumps have been used with a narrower electrode interval, and the bump structure has been used from a round ball bump having a columnar shape. Patent Document 1 discloses a columnar pillar bump having an extremely fine bump pitch. The pillar bumps have hemispherical solder formed at the tip of a pillar (columnar shape) such as Cu standing upright at a narrow pitch. The solder at the tip may be hemispherical, or may have a tip that is flattened into an ellipse. Therefore, the bump pitch can be made finer than that of a conventional solder ball type solder bump. Moreover, it can respond to high-density mounting. Since these solder portions have a very small area on the bottom surface of the pillar (column), solder joint portions are formed with an extremely small amount of solder as compared with conventional solder ball type solder bumps.

JP 2006-245288 A

  When a chip on which such pillar bumps are formed is thermocompression-bonded to a substrate and the bonding state is to be inspected, there are the following problems.

  The alignment between the chip and the substrate is performed by recognizing the alignment marks provided on the chip and the substrate and driving the thermocompression tool for holding the chip or the substrate stage for holding the substrate based on the image recognition data. doing. Therefore, even if the chip and the substrate are aligned based on the alignment mark, if the center position of the pillar bump and the electrode of the substrate exceeds the predetermined range, the pillar bump will be displaced from the electrode when the chip is pressed. (In particular, pillar bumps with fine bump pitches have a narrow alignment margin, making it difficult to align the pillar bumps with the electrodes). Bonding between the chip and the substrate in a state where the pillar bump is displaced from the electrode causes a problem such as a short circuit.

  Also, since the amount of solder provided at the tip of the pillar bump is smaller than that of the conventional ball bump, depending on the balance between the heating of the solder by the heater and the pressing force of the chip, the molten solder between the pillar and the electrode There is also a problem that the material is crushed and protrudes from the joint surface of the electrode.

  Accordingly, an object of the present invention is to provide a mounting method in which a chip on which fine solder bumps such as pillar bumps are formed is thermocompression-bonded to a substrate. A method and mounting apparatus are provided.

In order to solve the above-mentioned problem, the invention described in claim 1
A mounting method in which a pillar bump in which solder is formed on a tip of a pillar provided on a chip is heated and thermocompression bonded to an electrode provided on a substrate while being pressed,
Holding the chip with a thermocompression bonding tool and lowering it to the substrate side;
A first height measuring step for measuring a raising / lowering position of a thermocompression bonding tool holding the chip at a timing when it is detected that the pillar bump of the chip is in contact with the electrode of the substrate;
In a state where the solder is softened by preheating, the softened solder will not be crushed, and the thermocompression bonding that holds the chip after pressing the chip to the substrate side for a preset time with a preset weight. A second height measuring step for measuring the lift position of the tool;
From the measurement result of the first height measurement process and the measurement result of the second height measurement process, a change in the distance between the chip and the substrate due to the pressing of the chip is obtained. And a sinking amount determination step for determining whether or not the alignment of the electrodes is good.

  According to the first aspect of the present invention, after a chip having pillar bumps, on which solder is formed at the tip of the pillar, is held by the thermocompression bonding tool and lowered to the substrate side, the pillar bump of the chip contacts the electrode of the substrate. The raising / lowering position of the thermocompression bonding tool holding the chip is measured (first height measurement step).

  Then, in a state where the solder is softened by preheating, the softened solder is not crushed, and the chip is held after pressing the chip to the substrate side for a preset time with a preset weight. The raising / lowering position of the thermocompression bonding tool is measured (second height measurement step).

  Then, from the measurement result of the first height measurement process and the measurement result of the second height measurement process, a change in the gap between the chip and the substrate due to the pressing is obtained, and the pillar bump and the electrode are in a stage before the solder is melted. Is determined (subduction amount determination step).

  In a state where the pillar bumps of the chip are in contact with the electrodes of the substrate, the temperature of the thermocompression bonding tool is not increased, so that the solder of the pillar bumps is in a solid phase that is not melted. Therefore, when the contact position of the solder of the pillar bump is aligned with the range of the bonding surface of the electrode of the substrate, the solder at the tip of the pillar bump comes into contact with the bonding surface of the electrode. In this state, even if the chip is pressed against the substrate only for a preset pressure and for a preset time, only the deformation of the solder of the pillar bump accompanying the press will change the gap between the chip and the substrate. . However, when the contact position of the solder of the pillar bump is out of the contact surface of the electrode, and is in contact with the end of the contact surface of the electrode, if the chip is pressed with a predetermined pressure for a predetermined time, the contact surface of the electrode Since the reaction force from is not sufficient, the chip sinks to the substrate side with the pressing amount. Therefore, the gap between the chip and the substrate is narrower than in the case where the solder at the tip of the pillar bump is aligned within the bonding surface of the electrode.

  Accordingly, the measurement result of the first height measurement process, which is the raising / lowering position of the thermocompression bonding tool in which the pillar bump contacts the electrode, and the second raising / lowering position of the thermocompression bonding tool after pressing the chip at a predetermined pressure for a predetermined time. By determining the change in the gap between the chip and the substrate from the measurement result of the height measurement step, it is possible to determine whether the alignment of the solder of the pillar bump and the electrode is well performed before the solder is melted ( Subduction amount judgment process).

The invention described in claim 2
A thermocompression bonding tool for holding a chip provided with pillar bumps in which solder is formed at the tip of the pillar;
A substrate stage for holding a substrate having electrodes to which the pillar bumps of the chip are bonded;
Driving means for moving the thermocompression bonding tool holding the chip up and down toward the substrate stage holding the substrate;
A height detection means for detecting the raising and lowering position of the thermocompression bonding tool holding the chip;
A load detecting means for detecting a pressing force when the thermocompression bonding tool holding the chip presses the substrate;
A heater for raising the temperature of the thermocompression bonding tool;
A mounting apparatus comprising: a control unit that measures chip height position information by the height detection unit, measures a pressing force to the chip by the load detection unit, and controls the driving unit and the heater. ,
The control means is
The timing at which it was detected that the pillar bump of the chip contacted the electrode of the substrate,
In a state where the solder is softened by preheating, the softened solder will not be crushed, with a preset weight, a preset time, and a timing when the chip is pressed to the substrate side ,
From a change in the switch-up and substrate distance, at the front solder melting step, a mounting device having a function of determining the quality of alignment of the pillar bump and the electrode.

  According to the second aspect of the present invention, the control means has a predetermined load in which the softened solder is not crushed in a state where the solder is softened by preheating after the pillar bump of the chip contacts the bonding surface of the electrode of the substrate. The chip is pressed to the substrate side for a predetermined time. It has a function of measuring the change in the gap between the chip and the substrate due to the pressing by the height detecting means and determining whether the alignment of the solder of the pillar bump and the electrode before melting is good or bad.

  By lowering the thermocompression bonding tool, the position where the pillar bump of the chip held by the thermocompression bonding tool is contacted is measured by the height detection means, and the pressing force of the chip is maintained at a predetermined value by the load detection means for a predetermined time, Pressing. The change in the gap between the chip and the substrate can be measured by measuring the position of the thermocompression bonding tool when the pressing is completed with the height detection means.

  If the pillar bumps of the chip are aligned with the bonding surfaces of the electrodes, the solder of the pillar bumps before the solder is melted is deformed according to the amount of pressing because of the solid state, and the amount of deformation is a change in the gap between the chip and the substrate. Become. However, when the pillar bump and the electrode are aligned, if the pillar bump is positioned at the end of the joint surface of the electrode, the chip sinks to the substrate side according to the pressing force. In such a case, when the pressing is completed, the gap between the chip and the substrate becomes narrower than in the case where the pillar bump and the electrode are aligned. Since the control means for judging whether or not the alignment is good from the change in the gap between the chip and the substrate is used, the position deviation of the pillar bumps can be detected well before the solder is melted.

  According to the present invention, in a mounting method and a mounting apparatus in which a pillar bump, on which solder is formed on a tip of a pillar provided on a chip, is heated and pressed against an electrode provided on a substrate while being pressed, At a stage, it can be determined whether the solder of the pillar bump and the electrode are well aligned.

It is a schematic side view of the mounting apparatus according to the present invention. It is a schematic side view which shows the relationship between a chip | tip and a board | substrate. It is a flowchart explaining the mounting method which concerns on this invention. It is a chart which shows Z-axis head height and a detected load. It is a side view which shows the state of a chip | tip and a board | substrate, and is a figure explaining the relationship between a detection load and Z-axis head height.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side view of a mounting apparatus according to an embodiment of the present invention, and FIG. 2 is a side view of a chip 2 and a substrate 6 used in the mounting apparatus. In FIG. 1, the left-right direction toward the mounting apparatus 1 is an X-axis, the front-rear direction is a Y-axis, an axis orthogonal to the XY plane composed of the X-axis and the Y-axis is a Z-axis, and the Z-axis is the θ-axis.

  The mounting apparatus 1 includes a head 8 for sucking and holding the chip 2, a substrate stage 11 for sucking and holding the substrate 6, a two-field camera 13 for recognizing alignment marks provided on the chip 2 and the substrate 6, and the mounting apparatus 1. It is comprised from the control part 20 which controls the whole.

  The head 8 has a built-in load cell 10 that detects the pressure applied to the chip 2. A tool 9 for sucking and holding the chip 2 is attached to the lower side of the head 8. The tool 9 incorporates a heater 16 and a thermocouple 18 so that the chip 2 can be heated based on a command from the control unit 20 (the heater 16 is indicated by a dotted line in FIG. 1). The head 8 moves up and down in the Z direction by driving and controlling the servo motor 14 and the ball screw 15 connected to the servo motor 14. The drive means of the present invention is composed of a servo motor 14 and a ball screw 15.

  Further, the head 8 is configured to be able to perform load control for controlling the pressing force and position control for controlling the Z-axis height position based on a command from the control unit 20. The thermocompression bonding tool of the present invention includes a head 8 and a tool 9.

  The pressing force of the head 8 is preferably controlled by the torque of the motor, but any means that generates a pressing force such as a voice coil motor or a pneumatic cylinder may be used.

  The amount of movement that fluctuates in the Z direction in order to keep the pressing force constant during load control is configured so that position information can be acquired by position detection means by the encoder 19 of the servo motor 14. As long as the position detecting means can measure the position in the Z direction, a linear scale or the like may be used outside.

  The substrate stage 11 can be moved in the X, Y, and θ directions by a drive mechanism (not shown), and is configured so that the suctioned and held substrate 6 can be positioned at a predetermined position.

  The two-field camera 13 is inserted between the chip 2 sucked and held by the tool 9 and the circuit board 6 sucked and held by the substrate stage 11, and recognizes the alignment marks attached to the chip 2 and the substrate 6. can do. Usually, it stands by at the standby position (dotted line notation in FIG. 1) and can move to the image recognition position (between the chip 2 and the substrate 6) during image recognition.

  As shown in FIG. 2A, the chip 2 is provided with a Cu pillar 4 (copper post) on the chip back surface 2b. Solder 5 is formed at the tip of the pillar 4. A pillar bump 3 is formed by the pillar 4 and the solder 5. An electrode 7 is provided on the substrate 6, and the surface of the electrode 7 is subjected to solder plating 7a. An adhesive 17 that is a non-conductive thermosetting resin is filled around the electrode 7 of the substrate 6. The electrode 7 is provided with a flat bonding surface 7 b to be bonded to the pillar bump 3.

  The pillar 4 made of Cu has a cylindrical shape. The pillar 4 is not limited to a cylindrical shape, and may be a polygonal column or a conical column as long as the solder 5 is formed at the tip of the column. For example, the shape as shown in FIG.

  A mounting method for mounting the chip 2 on the substrate 6 using the mounting apparatus 1 will be described with reference to the flowchart of FIG. 3 and the graph for explaining the mounting state of FIG. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the height of the head 8 in the Z-axis direction and the detected load of the load cell 10.

  First, the chip 2 is sucked and held by the tool 9 of the head 8, and the head 8 is lowered to a predetermined height (search height) toward the substrate 6 while the substrate 6 is sucked and held by the substrate stage 11. Start with. In advance, the alignment mark on the chip 2 and the alignment mark on the substrate 6 are image-recognized by a two-field camera, and the substrate stage 11 is aligned in the X, Y, and θ directions based on the image recognition data. The heater 16 of the tool 9 is warmed to the preheating temperature T1. At the preheating temperature T1, the solder is in a softened state (for example, 160 ° C.) that moves from the solid phase state to the molten state. In the drive control of the head 8, the servo motor 14 is driven based on the detection position of the encoder 19 which is a height detection means, and the position is controlled (step ST00).

  Next, the chip head 8 is lowered by a predetermined height at a low speed. The pillar bump 3 descends while pushing away the adhesive 17 around the electrode 7. This state is the timing at t0 in FIG. The bump 3 approaches the vicinity of the electrode 7. The head 8 gradually descends, and a search operation is performed to detect the timing at which the solder 5 at the tip of the pillar bump 3 contacts the electrode 7 (step ST01).

  Next, the load P1 is detected by the load cell 10 (step ST02). The load P1 is set as a search load. The timing t1 in FIG. 4 is the timing when the solder 5 of the bump 3 contacts the electrode 7. The drive control of the head 8 is switched to load control based on the detected load of the load cell 10.

  When the solder 5 of the pillar bump 3 contacts the electrode 7, the temperature of the tool 9 heated to the preheating temperature T1 is transmitted to the substrate 6 side.

  Further, the adhesive 17 prefilled in the substrate 6 is pushed out from the contact portion between the bump 3 and the electrode 7 when the chip 2 is pressed against the substrate 6 with the search load P1. This process is performed because if the adhesive 17 remains between the pillar bumps 3 and the electrodes 7, a product failure occurs in a later process.

  Next, the search load P1 is maintained for a predetermined time tm1 (step ST03). The chip 2 is provided with a plurality of pillar bumps 3. The height of each pillar bump 3 is slightly different. Therefore, all the pillar bumps 3 are grounded to the joint surface 7b of the electrode 7 by maintaining the search weight P1 for a predetermined time tm1.

  Next, the height position H1 of the head 8 is measured by the encoder 19 which is a height detection means of the head 8, and stored in the control unit 20 (step ST04). The measurement is performed at timing t2 in FIG. The measurement of the height position H1 corresponds to the first height measurement process of the present invention.

  Next, the set load of the head 8 is changed to P2 (step ST05). In a preheating state (for example, a state of about 160 ° C.), the solder 5 formed at the tip of the pillar bump 3 is not melted. The solder 5 is in a softened state at the stage of transition from the solid phase state to the liquid phase state. Therefore, when the head 8 is load-controlled with the set load P2, the softened solder 5 is pushed into the electrode 7 and the shape is deformed.

Next, for a predetermined time tm2 from timing t3 to t4 in FIG.
Control the load with.

  Next, the height position H2 of the head 8 is measured by the encoder 19 which is a height detection means of the head 8, and stored in the control unit 20 (step ST06). The measurement of the height position H2 corresponds to the second height measurement process of the present invention.

  By changing the setting load P1 of the load control of the head 8 from P1 to P2, the pillar bump 3 is pushed into the electrode 7. At this time, when the bonding surface 7b of the pillar bump 3 and the electrode 7 is displaced, the height displacement amount (H1-H2) of the head 8 measured in step ST04 and step ST06 is set as a permissible value. Ha will be exceeded. Therefore, after performing load control for a predetermined time tm2 with the set load P2, it is determined whether or not the height displacement amount (H1-H2) of the head 8 is within the allowable value Ha (step ST07). The determination is made at timing t4 in FIG. The height displacement amount (H1-H2) of the head 8 corresponds to the change in the gap between the chip 2 and the substrate 6, and whether or not it is within the allowable value Ha is determined by the solder bump and the electrode before melting according to the present invention. This corresponds to a sinking amount determination step for determining whether or not the alignment is good. If the height displacement amount (H1-H2) of the head 8 exceeding the allowable value Ha is detected, the control unit 20 stores that there is a misalignment defect between the solder 5 and the electrode 7 on the working substrate 6 (step). ST07NG).

  The allowable value Ha is set based on the case where the solder 5 of the pillar bump 3 is aligned near the center of the bonding surface 7b of the electrode 7. When the contact position between the solder 5 and the joint surface 7b is displaced and is in contact with the end of the electrode 7, if the chip 2 is pressed for a predetermined time tm2 with the set load P2, the reaction force from the electrode 7 is sufficient. Therefore, the chip 2 sinks to the substrate 6 side with the pressing amount.

  Accordingly, by detecting the height displacement amount of the head 8 that exceeds the allowable value Ha, it is possible to determine whether the solder 5 of the pillar bump 3 and the contact surface 7b of the electrode 7 are well aligned.

  As the set load P2, a load that does not collapse in a state where the solder 5 is heated to the preheating temperature T1 and softened is measured in advance and stored in the control unit 20 and used in an actual process. Therefore, the solder 5 does not endure the load P2 and does not collapse.

  Next, the drive control of the head 8 is switched from the load control based on the detected load of the load cell 10 to the position control based on the detected position of the encoder 19 which is a height detecting means. Thereby, position control is performed so that the distance between the pillar bump 3 and the electrode 7 is kept constant. Next, the set temperature of the heater 16 is changed to T2. At the temperature T2, the solder 5 at the tip of the bump 3 reaches the solder melting temperature (for example, 240 to 280 ° C.).

  Next, after a predetermined time tm3 has elapsed, the head 8 is further lowered toward the substrate 6 by the pushing amount Hb, and the pillar bump 3 is pushed into the electrode 7 (step ST08). The pushing is performed at timing t5 in FIG. When the pillar bump 3 is pushed into the electrode 7, a reaction force is generated. The reaction force is measured as the detected load P3 of the head 8 by the load cell 10 when the push-in is completed (timing t6 in FIG. 4) (step ST09). The measurement of the detected load P3 corresponds to the first reaction force measurement step of the present invention.

  Next, after elapse of a predetermined time tm4, the load P10 measures the detected load P4 of the head 8. The measurement of the detected load P4 is performed at a stage where the load fluctuation of the head 8 is generated and stabilized (timing t7 in FIG. 4) and the solder 5 is melted (step ST10). The measurement of the detected load P4 corresponds to the second reaction force measurement step of the present invention. Since the position of the head 8 is controlled so as to maintain the pushing amount Hb, the reaction force (detected load P3) generated when the pillar bump 3 is pushed into the electrode 7 decreases as the solder 5 melts. Since the solder 5 is heated at the temperature T2, the solder 5 has reached the melting temperature. Further, the adhesive 17 filled between the chip 2 and the substrate 6 is cured.

  When the alignment of the pillar bump 3 and the electrode 7 is performed with high accuracy, the reaction force (detected load P4) generated between the molten solder 5 and the electrode 7 maintains a predetermined value. However, when the alignment between the pillar bump 3 and the electrode 7 is misaligned, the reaction force from the molten electrode 7 does not act on the pillar bump 3, so the detected load P4 is used when the alignment is performed with high accuracy. Compared to lower. Based on this characteristic, it is determined from the detected load P3 and the detected load P4 whether the difference (P3-P4) is within the preset allowable value Hb (step ST11). If P3-P4 is within the allowable value Hb, it is determined that the alignment of the pillar bump 3 and the electrode 7 is accurately performed. If it is out of the range, the alignment of the pillar bump 3 and the electrode 7 is displaced. It is determined that This pass / fail determination corresponds to the reaction force determination step of determining the pass / fail alignment of the melted pillar bump 3 and the electrode 7 of the present invention. If the allowable value Hb is exceeded, the control unit 20 stores that there is a misalignment between the pillar bump 3 and the electrode 7 (step ST11NG).

  Next, the heater 16 is turned off, the suction holding of the chip 2 by the tool 9 is released, the head 8 is raised, and the mounting of the chip 2 on the substrate 6 is finished (step ST12).

  Regarding the reaction force determination step, the state of the solder 5 of the chip 2 and the electrode 7 of the substrate 6 will be described in detail with reference to FIG. FIG. 5 shows the positional relationship between the chip 2 and the substrate 6 in the processes from step ST01 to step ST10. FIG. 5A shows a state where the bump 3 of the chip 2 is in contact with the electrode 7 (step ST02). The distance between the back surface 2b of the chip 2 in this state and the substrate 6 is h0. The detected load is P1, and the height H1 of the head 8 is maintained.

  FIG. 5B shows a state (step ST06) in which the bump 3 of the chip 2 is pressed against the electrode 7 with a predetermined load (a load in which the pillar 4 and the electrode 6 do not contact). The distance between the back surface 2b of the chip 2 in this state and the substrate 6 is h1. The detected load is P2, and the head height H2 is maintained.

  FIG. 5C shows a state where the bump 3 of the chip 2 is pushed into the electrode by a predetermined pushing amount Hb (step ST09) and the solder 5 reaches the melting temperature (step ST10). In this state, the solder 5 and the electrode 7 are aligned with high accuracy. For this reason, the reaction force generated between the solder 5 and the electrode 7 maintains a predetermined value even in the solder melted state.

  On the other hand, FIG. 5D shows a case where the solder 5 and the electrode 7 are misaligned. Since the positions of the melted solder 5 and the electrode 7 are shifted, the reaction force from the electrode 7 is not transmitted to the solder 5. Therefore, the detected load P4 is lower than that in a state where the detection load P4 is accurately aligned.

  Specifically, for each production lot of the chip 2 and the substrate 6, the values of the detected loads P3 and P4 with respect to the pushing amount Hb are stored in the control unit 20 in advance. In addition, a setting value is stored in the control unit 20 with respect to the detected load P4 when a positional deviation occurs. Based on these data, the detected loads P3 and P4 are compared for each joining of the chip 2 and the substrate 6, and the quality of the joining is judged.

DESCRIPTION OF SYMBOLS 1 Mounting apparatus 2 Chip 2b Chip back surface 3 Pillar bump 4 Pillar 5 Solder 6 Substrate 7 Electrode 7a Solder plating 7b Join surface 8 Head 9 Tool 10 Load cell 11 Substrate stage 13 2 Field of view camera 14 Servo motor 15 Ball screw 16 Heater 17 Adhesive 18 Thermoelectric Vs. 19 encoder 20 control unit T1 preheating temperature T2 solder melting temperature

Claims (2)

A mounting method in which a pillar bump in which solder is formed on a tip of a pillar provided on a chip is heated and thermocompression bonded to an electrode provided on a substrate while being pressed,
Holding the chip with a thermocompression bonding tool and lowering it to the substrate side;
A first height measuring step for measuring a raising / lowering position of a thermocompression bonding tool holding the chip at a timing when it is detected that the pillar bump of the chip is in contact with the electrode of the substrate;
In a state where the solder is softened by preheating, the softened solder will not be crushed, and the thermocompression bonding that holds the chip after pressing the chip to the substrate side for a preset time with a preset weight. A second height measuring step for measuring the lift position of the tool;
From the measurement result of the first height measurement process and the measurement result of the second height measurement process, a change in the distance between the chip and the substrate due to the pressing of the chip is obtained. And a sinking amount determination step for determining whether the alignment of the electrodes is good or bad. A thermocompression bonding tool for holding a chip provided with pillar bumps in which solder is formed at the tip of the pillar;
A substrate stage for holding a substrate having electrodes to which the pillar bumps of the chip are bonded;
Driving means for moving the thermocompression bonding tool holding the chip up and down toward the substrate stage holding the substrate;
A height detection means for detecting the raising and lowering position of the thermocompression bonding tool holding the chip;
A load detecting means for detecting a pressing force when the thermocompression bonding tool holding the chip presses the substrate;
A heater for raising the temperature of the thermocompression bonding tool;
A mounting apparatus comprising: a control unit that measures chip height position information by the height detection unit, measures a pressing force to the chip by the load detection unit, and controls the driving unit and the heater. ,
The control means is
The timing at which it was detected that the pillar bump of the chip contacted the electrode of the substrate,
In a state where the solder is softened by preheating, the softened solder will not be crushed, with a preset weight, a preset time, and a timing when the chip is pressed to the substrate side ,
From a change in the switch-up and substrate distance, at the front solder melting step, mounting device having a function of determining the quality of alignment of the pillar bump and the electrode.

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