Die bonder and bonding method

With a die bonder or a bonding method, the die is adsorbed by the collet, the dicing tape to which the die is adsorbed is thrust up, the die adsorbed by the collet, and thrust up is peeled from the dicing tape, and the peeled die is bonded to the substrate. When the decrease in the air leak flow rate through the gap between the collet and the die upon the thrust up is smaller than the decrease in the normal peel by a predetermined amount, it is judged that a deflection occurs in the die.

BACKGROUND OF THE INVENTION

The present invention relates to a die bonder and a bonding method, and more particularly, to a die bonder and a bonding method which are highly reliable.

RELATED ART

A process of assembling a package by mounting a die (semiconductor chip)(hereinafter simply referred to as a die) onto a substrate such as a wiring substrate and a lead frame includes a step of separating a die from a semiconductor wafer (hereinafter simply referred to as a wafer), and a die bonding step of bonding the separated dies onto the substrate.

The bonding step includes a peeling step that peels the dies separated from the wafer. In the peeling step, each die is peeled from a dicing tape held by a pickup device one by one, and is further conveyed onto the substrate using a suction jig called collet.

JP-A No. 2002-184836 and JP-A No. 2007-42996 disclose the peeling step as generally employed technique. JP-A No. 2002-184836 discloses that a group of first thrust-up pins provided at four corners of the die, and a group of second thrust-up pins provided at the center or peripheral portion of the die each having a leading end lower than that of the first thrust-up pin are attached to a pin holder which is lifted for peeling.

JP-A No. 2007-42996 discloses that three blocks are arranged so as to allow the thrust-up height to be higher as the position is closer to the center of the die. A protrusion that protrudes toward the corner of the die is integrally formed at each of the four corners of the block at the outermost side so that the three blocks are sequentially thrust up.

The above-described related art monitors the flow rate of the air leaking to the collet when picking up of the die to judge whether or not crack occurs in the die.

SUMMARY OF THE INVENTION

Recently, an effort to reduce the package thickness has been in progress for the purpose of promoting high-density packaging of a semiconductor device. Especially, the stacked package that allows a plurality of dies to be three-dimensionally mounted onto the wiring substrate of the memory card has been put into practical use. Assembly of the stacked package requires reduction of the die thickness to 20 μm or smaller in order to prevent increase in the package thickness.

As the thickness of the die is reduced, rigidity of the die is significantly deteriorated compared to the adhesive power of the dicing tape. This may cause the risk of increasing the possibility to cause the crack in the die to be higher than the generally employed case. It is therefore important to monitor whether or not the crack occurs in the die when conducting the multistage thrust-up pin method using the groups of the first and the second pins with different heights as disclosed in JP-A No. 2002-184836, and the multistage block method with protruding portion as disclosed in JP-A No. 2007-42996.

However, the generally employed technique is not capable of judging occurrence of deflection if no crack occurs. Especially, even a large deflection amount which may cause the non-conforming product cannot be detected.

The present invention provides a highly reliable die bonder capable of judging occurrence of the deflection in the case where no crack occurs in the die.

Characteristics of the present invention will be described as below.

The present invention provides a die bonder and a bonding method as a first characteristic that the die is adsorbed by the collet, the dicing tape to which the die is adsorbed is thrust up, the die adsorbed by the collet, and thrust up is peeled from the dicing tape is placed on a substrate, and the peeled die is bonded to the substrate. When a decrease in an air leak flow rate through the gap between the collet and the die upon the thrust up is smaller than the decrease in the normal peel by a predetermined amount, a first judgment is made that a deflection occurs in the die.

As a second characteristic of the present invention, the first judgment is made based on the decrease in the air leak flow rate by means of a differential value.

As a third characteristic of the present invention, a second judgment is made that a crack occurs in the die when the air leak flow rate becomes constant or substantially constant.

As a fourth characteristic of the present invention, the first judgment is made that the peel is normally done in spite of the deflection when the air leak flow rate becomes equal to or smaller than a first predetermined value, or the decrease in the air leak flow rate is equal to or smaller than a second predetermined value within a predetermined time.

As a fifth characteristic of the present invention, the thrust up operation thrusts the dicing tape upward at a predetermined portion of a peripheral portion of the die to form a peel start point. A judgment is made with respect to the deflection upon formation of the peel start point.

As a sixth characteristic of the present invention, the peel start point is formed at the predetermined portion provided at least at one corner portion of four corner portions of the die.

The present invention provides highly reliable die bonder and bonding method which are capable of judging occurrence of the deflection even if no crack occurs in the die when it is picked up.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described referring to the drawings.

FIG. 1is a conceptual view of a die bonder10as an embodiment of the present invention, seen from above. The die bonder is mainly formed of a wafer supply unit1, a work supply/carry-out unit2and a die bonding unit3.

The work supply/carry-out unit2includes a stack loader21, a frame feeder22and an unloader23. A work (substrate such as the lead frame, or the die already mounted onto the substrate) supplied to the frame feeder22by the stack loader21is conveyed to the unloader23via two processing positions on the frame feeder22.

The die bonding unit3includes a preform portion31and a bonding head portion32. The preform portion31applies a die adhesive agent to the incoming work fed by the frame feeder22. The bonding head portion32picks up the die from a pickup device12, and ascends to move the die in parallel to a bonding point on the frame feeder22. The bonding head portion32descends the die so as to be bonded to the work to which the die adhesive agent has been applied.

The wafer supply unit1includes a wafer cassette lifter11and the pickup device12. The wafer cassette lifter11includes a wafer cassette (not shown) loaded with wafer rings which are sequentially supplied to the pickup device12.

The embodiment is of a type which allows a bonding head35of the bonding head portion32to pick up the die. Alternatively, the pickup head for exclusive use of the pickup may be added apart from the bonding head35so that the die picked up by the pickup head is placed at a predetermined position, and the placed die is picked up by the bonding head.

The structure of the pickup device12will be described referring toFIGS. 2 and 3.FIG. 2is a perspective view showing an outer appearance of the pickup device12.FIG. 3is a sectional view schematically showing a main part of the pickup device12. Referring toFIGS. 2 and 3, the pickup device12includes an expand ring15that holds the wafer ring14, a support ring17that is held by the wafer ring14, and horizontally positions the dicing tape16to which a plurality of dies (chip)4are adhered, and a thrust-up unit50that is provided inside the support ring17for thrusting the die4upward. The thrust-up unit50is configured to be driven by a not shown drive mechanism to move in a vertical direction. The pickup device12is moved in a horizontal direction.

The pickup device12descends the expand ring15that holds the wafer ring14upon thrust up of the die4. As a result, the dicing tape16held by the wafer ring14is stretched to widen the interval between the dies4, and the die4is thrust up by the thrust-up unit50from below so as to facilitate the pickup operation of the die4. Along with the thickness reduction, the adhesive agent in the liquid state is transformed to be in the film state. A film-like adhesive material called a die attach film18is applied between the wafer and the dicing tape16. In the case where the wafer has the die attach film18, the dicing is performed with respect to the wafer and the die attach film18. In the peeling step, the wafer and the die attach film18are peeled from the dicing tape16.

FIG. 4shows structures of the thrust-up unit50and a collet portion40of the bond head unit (not shown) according to the embodiment of the present invention.FIG. 5is a view of the part on which a thrust-up block portion and the pin forming a peel start point (the following, expressed as “peel start point forming pin”) of the thrust-up unit exist when seen from above.

Referring toFIG. 4, the collet portion40includes a collet42, a collet holder41that holds the collet42, and suction holes41vand42vfor adsorbing the die4.

Meanwhile, the thrust-up unit50is mainly formed of the thrust-up block portion, the peel start point forming pin portion, a drive unit that drives the thrust-up block portion and the peel start point forming pin portion, and a dome body58that holds those elements as described above. The thrust-up block portion includes a block body59, an inner block54directly connected to the block body59, and an outer block52that is provided around the inner block via a ½ switching spring52band has an outer shape smaller than that of the die4.

Referring toFIG. 5, the peel start point forming pin portion includes four peel start point forming pins51respectively formed outside the four corners of the outer block52, that is, at four corners of the die, pin vertical links55that hold the peel start point forming pins, and are vertically movable, and pin drive links56that rotate around points56aas supporting points to move the pin vertical links55in the vertical direction.

The drive unit includes a drive shaft57that is driven by a motor to move in the vertical direction, and an operation body53that moves vertically accompanied with the vertical motion of the drive shaft57. When the operation body53descends, the left and right pin drive links56are rotated to ascend the pin vertical links55to thrust up the peel start point forming pins51upward. When the operation body53ascends, the block body is moved upward to push the outer and inner blocks upward. As described above, the pin vertical links55and the pin drive links56form an inversion portion that transforms the descending motion of the operation body53into the thrust up (ascending) motion of the peel start point forming pin51.

A dome head58bhaving a large number of suction holes58a, which adsorbs and holds the die4is provided at the upper portion of the dome body58.FIG. 5shows only a unit in a single row around the block portion. However, the units in a plurality of rows are provided for the purpose of stably holding a die4dthat is not intended to be picked up. AsFIG. 5shows, a gap54vbetween the inner block54and the outer block52, and a gap52vbetween the outer block52and the dome head58bare adsorbed to hold the dicing tape16to the side of the block portion.

The thrust-up unit50as described above descends the peel start point forming pins51after ascending. However, they do not have to be necessarily descended. For example, the pins are ascended to form the peel start point, and then the outer and the inner blocks may be ascended as described later while holding the peel start point position.

The pickup operation performed by the above-described thrust-up unit50will be described referring toFIGS. 6A to 6D.FIGS. 6A to 6Dshow operations of a portion around the dome head58b, and the collet portion40upon the pickup operation.

Referring toFIG. 6A, the collet portion40descends to land on the dome head58bof the thrust-up unit50. At this time, the peel start point forming pins51, the outer block52, and the inner block54are in plane with the surface of the dome head58b. The dicing tape16and the die4are placed in the plane while being in a stable posture. After the landing, the collet42adsorbs the die4by means of the suction hole58aof the dome head58b, and the gaps52vand54vbetween the respective blocks.

FIG. 6Bshows that the peel start point forming pins51at four corners of the outer block52are only ascended by several tens to hundreds μm. The operation body53is descended to rotate the pin vertical links56around the point56aas the supporting point, which ascends the pin vertical links55, thus ascending the peel start point forming pins51. As the peel start point forming pins51are ascended, the dicing tape16therearound is raised to generate a thrust-up portion. A very small space is generated between the dicing tape16and the die attach film18, that is, the peel start point51ais generated. Such space significantly reduces the anchor effect that keeps the dicing tape16applied to the dome head58b, that is, the stress exerted to the die4. This ensures the peeling operation in the subsequent step. The peel start point forming pin51may have its leading end with a round shape having its diameter of 700 μm or smaller, or with a flat shape so long as a very small space is generated. A flange42tof the collet42is slightly deformed in connection with deformation of the die, thus preventing the air inflow.

FIG. 6Cshows the state where the operation body53is ascended to return the peel start point forming pin51to the original positions so that the outer block52and the inner block54are ascended together. The outer block52and the inner block54are ascended by separating the operation body53from the pin drive links56, and further ascending. When the operation body53is separated from the pin drive links56, the peel start point forming pin51is returned to the original point, which does not contribute to subsequent peeling operation. The position of the peel start point forming pin51may be retained without being returned to the original position.

FIG. 6Dshows the state where the operation body53is further ascended to ascend the inner block54only by action of the ½ switching spring52b. In this state, the contact area between the dicing tape16and the die4is sufficient to allow peeling by ascending the collet. The die4is peeled off by ascending the collet42.

As described above, the embodiment provides the peel start point forming pins51at positions corresponding to four corners of the die4, which are ascended at the initial stage of the peeling process so that the space serving as the point at which the peeling starts is generated. This makes it possible to reduce the stress exerted to the die4, and ensures the peeling process performed by the outer block52and the inner block54in the subsequent process.

This makes it possible to provide the highly reliable die bonder or the pickup method while reducing the pickup error.

The die peeling process described referring toFIGS. 6A to 6Dallows the peel start point forming pins51to perform the die peeling process. However, the die thickness reduction may cause crack in the die4during the thrust-up operation as shown inFIGS. 6B,6C and6D, or the deflection to exceed the acceptable value, thus failing to peel the die.

FIG. 7is an explanatory view representing the principle for making a judgment with respect to the normal peel, crack and deflection of the die during the thrust-up operation according to the embodiment. In the embodiment, the thrust-up operation is performed in three stages of ascending a peel start point forming pin51, the outer block52and the inner block54, and the inner block54. The upper portion of the view shown inFIG. 7represents the change in the air leak flow rate caused by the peel start point forming pins51. The lower portion of the view shown inFIG. 7represents the time between the peel start point forming pins51is ascending, and ranges of the time between the primary judgment and the secondary judgment are performing with respect to the state of the die which will be described later.

Substantially the same change curve is obtained when ascending the outer block52and the inner block52, and the inner block54as well although the air leak flow rate value differs. The judgment may be made in the same way as the case of the peel start point forming pins51.

AsFIG. 6Ashows, when the collet42lands on the die to start adsorbing, the upper portion ofFIG. 7indicates that the collet42is in tight contact with the die and the air leak flow rate L is converged to the low flow rate. Thereafter, asFIG. 6Bshows, when ascending the peel start point forming pins51, the flange42tof the collet42is deformed to suppress the air leak flow rate L in the initial stage. As the deformation at the end of the die4proceeds, the gap between the collet42and the die4is generated to gradually increase the air leak flow rate L until a peel start point forming time td.

Thereafter, the air leak flow rate L is decreased owing to adhesive power of the dicing tape. At this time, if there is no crack or no deflection occurs in the die4, or the peel is normally done while having the small deflection, the air leak flow rate L is gradually decreased into convergence as indicated by the broken line.

When the crack occurs in the process of decrease in the air leak flow rate L, the air leak flow rate L hardly changes from the time point at which the crack occurs, and is kept constant or substantially constant by dashed line. In the case with a low probability where the crack occurs before formation of the peel start point, the air leak flow rate L may be kept constant or substantially constant from the time point.

When the deflection occurs in the die4, decrease in the air leak flow rate L is alleviated in accordance with the deflection amount as indicated by the solid line. If the decrease is equal to or smaller than the predetermined value, it is returned to the normal air leak flow rate L.

Based on the phenomenon analysis, in the case where the air leak flow rate L is reversely changed from increase to decrease with the diminish curve or gradient at a predetermined level or higher, judgment is made as the normal peel, or probability of the crack. In the case where the air leak flow rate is decreased with the diminish curve or the gradient at a predetermined level or lower, it is judged that the deflection has occurred. In the case where the deflection occurs, monitoring is performed until the deflection amount is recovered to be in the predetermined range. If it is recovered, or the decrease in the deflection amount is in the range equal to or lower than the predetermined value, it is considered that the normal state is recovered. Accordingly, the judgment is made that the peel has been normally done. The former case ensures to assist with the die4to restore the normal state although the time for monitoring is prolonged, and the pickup processing time is also prolonged. Meanwhile, although it is likely that the latter case misses the die4which restores the normal state, the pickup processing time may be reduced. The aforementioned judgment will be referred to as a primary judgment. The primary judgment is made for a period from the time at which the peel start point forming pins start ascending to the time after an elapse of a predetermined time from completion of forming the peel start point.

After the elapse of the primary judgment time, the secondary judgment is made whether the air leak flow rate L is kept constant, or substantially constant, that is, the crack has occurred within a secondary judgment time as shown inFIG. 7. If the crack has not occurred, it is judged that the peel has been normally done. Supposing that the crack occurs during ascending of the peel start point forming pins51, it is judged that the crack has occurred immediately after starting the secondary judgment.

The data processing method for the primary and the secondary judgments is conducted using the differential value of the air leak flow rate L. Alternatively, the gradient value while prolonging the time, or the diminish amount or flow rate value after an elapse of the predetermined time may be used likewise the case of the differential value. In short, may be any data processing can understand the phenomenon described above.

The description with respect to the judgment will be made taking the differential value as an example. In this case, the differential value is expressed as ΔBL(=ΔL/Δt), and each suffix of j, k, 1 and 2 denotes the actual measurement value, allowable value, the primary judgment allowable value, and the secondary judgment allowable value. The judgment will be made as follows.

Primary Judgment

ΔBLj≧ΔBLk1: normal peel or crack

Secondary Judgment

Generally, the threshold value of the air leak flow rate is managed with a timer so as to judge with respect to the crack, and the processing time is prolonged by an amount corresponding to the waiting period of the timer. The embodiment is capable of judging with respect to the crack and deflection quickly. The quick judgment may reduce the processing time and improve the throughput.

FIG. 8is a flowchart of the pickup process steps.FIG. 9is a flowchart as a sub-routine of the process shown inFIG. 8, which will be executed for judgment with respect to the normal peel, crack and deflection upon thrust-up of the die based on the principle shown inFIG. 7.

The dicing tape16is adsorbed to the dome head58b(step1). The collet42is landed on the die4so as to be adsorbed (step2). Thereafter, the peel start point forming pins51are ascended to form the peel start point (step3). A judgment is made with respect to the normal peel, crack and deflection in step4parallel to the process for forming the peel start point (step4). In the judgment step shown inFIG. 9, the primary judgment process as described referring toFIG. 7is executed (step S1). If it is judged that the deflection has occurred based on the result of the primary judgment process (step S2), it is further judged whether or not the deflection is in an allowable range (step S3). If the deflection is in the allowable range, it is judged that the peel is normally done, and a normal flag is set (step S6). If the deflection is not in the allowable range, an abnormal flag is set (step S7).

If it is judged that the peel has been normally done or the crack has occurred in step S2, the secondary judgment process is executed (step S4). If it is judged that the peel has been normally done based on the result of the secondary judgment process (step S5), the normal flag is set (step S6), and the process returns to the main routine. If it is judged that the crack has occurred, the abnormal flat is set (step S7), and the process returns to the main routine.

Upon return to the main routine, it is judged whether the process may be continuously executed based on the normal and abnormal flags (step5). If the abnormal flag is set, the device is stopped (step17). If the normal flag is set, the outer block52and the inner block54are ascended together (step6), and steps7,8and17are executed likewise the steps4,5and17which are executed when the peel start point is formed.

If it is judged that the peel has been normally done in step8, the inner block54is ascended (step9), and steps10,11and17are executed likewise the steps4,5and17which are executed when the peel start point is formed.

If it is judged that the peel has been normally done in step11, the collet42is ascended to pick up the die4(step12). Thereafter, the adsorption of the dicing tape is released (step13), and the outer block and the inner block are returned to the original heights (step14). The thrust-up unit50is moved to the position where the next die is thrust up (step15). Finally, it is judged whether a predetermined number of dies have been processed (step16), and the process ends.

The embodiment as described above provides the highly reliable die bonder and the bonding method which allow judgment with respect to occurrence of the deflection if no crack occurs upon pickup of the die.

The embodiment as described above provides the die bonder and the bonding method with high yield, which are capable of judging with respect to the die that returns to the normal state even if the deflection occurs.

The embodiment as described above provides the die bonder and the bonding method with low throughput, which accelerate the transition to the next operation to shorten the processing time as the judgment with respect to occurrence of the crack and deflection is made at an earlier stage.

In the embodiment as described above, after formation of the peel start point using the peel start point forming pins, the outer block and the inner block are ascended. However, the embodiment is applicable to the type that peels using a large number of pins as disclosed in JP-A No. 2002-184836.

The embodiments according to the present invention have been described. It is to be understood that the present invention may be made into an alternative form, corrected, and modified based on the description. The present invention contains an alternative examples, correction or modification as described above within a scope of the present invention.