Method for mounting semiconductor element, and semiconductor device

0001The present invention relates to a method for mounting a semiconductor element and a semiconductor device.

0002When mounting a semiconductor optical element such as a light receiving element or a light emitting element on a substrate, it is important to accurately manage the junction gap (clearance) between the substrate and the semiconductor optical element. Conventionally, as a method of forming bumps (protruding electrodes) for joining a semiconductor optical element to a substrate, for example, a plating method of precipitating metal from a plating solution, a vapor deposition method of evaporating metal in a vacuum to form a film, and conductivity. A printing method or the like is known for pasting by a printing device. However, the plating method cannot be said to have sufficient bonding reliability for bonding at low temperatures, and is not suitable for mounting semiconductor optical devices. In addition, it is difficult to form a large bonding gap by the vapor deposition method or the printing method.

<p num="0003"><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2003-86877</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 4-273444</text></patcit></p>

<p num="0004"> This case was made in view of the above problems, and when mounting a semiconductor element on a substrate, a semiconductor capable of improving dimensional accuracy even if the design dimension of the junction gap between the substrate and the semiconductor element is large. An object of the present invention is to provide a method for mounting an element and a semiconductor device.</p>

<p num="0005"> According to one aspect of the present case, it is a mounting method for mounting a semiconductor element on a substrate, in which a step of attaching a first solder bonding material on a substrate-side pad formed on the substrate and a step of mounting the first solder bonding material on the first solder bonding material. Between the step of supplying the second solder bonding material having a melting point lower than that of the first solder bonding material and the element side pad formed on the semiconductor element facing the corresponding substrate side pad and the substrate. Reflow is performed at a step of arranging the semiconductor element so that a predetermined bonding gap is provided and a reflow temperature lower than the melting point of the first solder bonding material and higher than the melting point of the second solder bonding material. Provided is a method for mounting a semiconductor element, which comprises a reflow step of joining a first solder bonding material and a second solder bonding material.</p><p num="0006"> Further, according to another viewpoint of the present case, a substrate having a substrate-side pad formed on its surface, a semiconductor element mounted on the substrate and having an element-side pad corresponding to the substrate-side pad, the substrate-side pad, and the above. A solder bump for joining the element-side pad is provided, and the solder bump is provided between the first solder-bonded portion formed on the substrate-side pad and between the first solder-bonded portion and the element-side pad. The first solder joint and the second solder joint include a second solder joint that is interposed and has a melting point lower than that of the first solder joint, and the temperature of the first solder joint and the second solder joint is lower than the melting point of the first solder joint. Moreover, a semiconductor device is provided which is integrally joined by being reflowed at a reflow temperature higher than the melting point of the second solder joint.</p>

<p num="0007"> According to the present invention, when mounting a semiconductor element on a substrate, a method for mounting the semiconductor element and a semiconductor device capable of improving dimensional accuracy even if the design dimension of the junction gap between the substrate and the semiconductor element is large is provided. be able to.</p>

0008<figref num="1">It is a figure which shows schematic the cross-sectional structure of the semiconductor device which concerns on embodiment.</figref><figref num="2">It is a figure which shows the circuit board which concerns on embodiment.</figref><figref num="3">It is a figure which shows the process of attaching the high melting point solder ball to each substrate side pad of the circuit board which concerns on embodiment.</figref><figref num="4">It is a figure which shows the jig for forming a recess which concerns on embodiment.</figref><figref num="5">It is a figure which shows the recess formation process which concerns on embodiment.</figref><figref num="6">It is a figure which shows the sealing process which concerns on embodiment.</figref><figref num="7">It is a figure which shows the state which removed the recess forming jig from the high melting point solder ball after the sealing process which concerns on embodiment.</figref><figref num="8">It is a figure which shows the state which put the screen plate which concerns on embodiment on a circuit board.</figref><figref num="9">It is a figure which shows the process of supplying the low melting point solder paste which concerns on embodiment.</figref><figref num="10">It is a figure which shows the reflow process which concerns on embodiment.</figref><figref num="11">It is a figure which shows the process of filling the 2nd mold resin in the gap between the mold resin and the optical element silicon chip which concerns on embodiment.</figref><figref num="12">It is a figure which shows the sealing process which concerns on the modification.</figref><figref num="13">It is a figure which shows the screen plate 8A with a protrusion which concerns on the modification.</figref><figref num="14">It is a figure which shows the recess formation process which concerns on the modification.</figref><figref num="15">It is a figure which shows the process of supplying the low melting point solder paste which concerns on the modification.</figref><figref num="16">It is a figure which shows the state which removed the screen plate with a protrusion from the circuit board which concerns on a modification.</figref><figref num="17">It is a figure which shows the reflow process which concerns on the modification.</figref><figref num="18">It is a figure which shows the process of filling the 2nd mold resin in the gap between the mold resin which concerns on a modification, and an optical element silicon chip.</figref>

0009&lt;Embodiment&gt; Hereinafter, the method of mounting the semiconductor device and the semiconductor element according to the present case will be described in detail with reference to the drawings.

0010&lt;&lt; Semiconductor device &gt;&gt; FIG. 1 is a diagram schematically showing a cross-sectional structure of the semiconductor device 1 according to the embodiment. The semiconductor device 1 is an optical module including a circuit board 2 and an optical element silicon chip 3 which is a semiconductor optical element mounted on the circuit board 2. The optical element silicon chip 3 in the present embodiment is, for example, a VCSEL (Vertical Cavity Semicond μctor Em). Ission Laser) and other light emitting elements, such as the light emitting unit 31 and the waveguide (optical transmission line) 32. Etc. Further, the circuit board 2 includes a light receiving unit 21 that receives the light output from the light emitting unit 31 of the optical element silicon chip 3, a waveguide (optical transmission line) 22 that receives the light received by the light receiving unit 21, and the like (not shown). ing. The solder bump 4 is a protruding electrode formed by solder. The circuit board 2 and the optical element silicon chip 3 are joined via solder bumps 4. The circuit board 2 and the optical element silicon chip 3 are examples of a substrate and a semiconductor element, respectively.

0011Reference numeral 2a represents the upper surface of the circuit board 2, and reference numeral 3a represents the lower surface of the optical element silicon chip 3. As shown in FIG. 1, the optical element silicon chip 3 is flip-chip bonded to the upper surface 2a of the circuit board 2 via the solder bump 4, and the lower surface 3a of the optical element silicon chip 3 and the upper surface 2a of the circuit board 2 Are arranged facing each other. The reference numeral Gc represents a "junction gap" (also referred to as "junction clearance"), which is a dimension in which the upper surface 2a of the circuit board 2 and the lower surface 3a of the optical element silicon chip 3 are separated from each other. In the present embodiment, the size of the junction gap Gc in the semiconductor device 1 is not particularly limited, but is set to, for example, about 200 μm.

0012By the way, in a so-called optical module such as the semiconductor device 1 according to the present embodiment, it is necessary to accurately realize the junction gap Gc according to the design value in order to secure the optical transmission characteristics of the optical element silicon chip 3. .. Since the optical element silicon chip 3 and the circuit board 2 are joined via the solder bumps 4, high accuracy in the height direction of the solder bumps 4 is required. Further, many semiconductor optical devices such as the optical element silicon chip 3 have a relatively low heat resistant temperature, for example, about 160 to 180 ° C. Therefore, when mounting the optical element silicon chip 3, there is a restriction that the reflow temperature cannot be raised so much in consideration of the heat resistant temperature of the optical element silicon chip 3. Here, as a conventional bump forming method, a plating method, a vapor deposition method, a printing method and the like are known. However, the plating method does not have sufficient bonding reliability for bonding at low temperatures, and it is difficult to form a large bonding gap with the thin-film deposition method or printing method. It can be said that the method of is not very suitable.

0013Therefore, in the semiconductor device 1 according to the present embodiment, the solder bump 4 for joining the circuit board 2 and the optical element silicon chip 3 is formed by including the high melting point solder joint portion 41 and the low melting point solder joint portion 42. did. The high melting point solder joint 41 is a solder ball formed of high melting point solder (high temperature solder) such as SnAgCu-based solder (tin-silver-copper solder). On the other hand, the low melting point solder joint 42 is formed of low melting point solder (low temperature solder) such as SnBi type solder (tin-bismuth type solder). The melting point of the low melting point solder joint 42 (for example, about 139 ° C) is lower than the melting point of the high melting point solder joint 41 (for example, about 220 ° C).

0014Here, the high melting point solder bonding portion 41 is bonded to an electrode pad (hereinafter, referred to as board side pad) 23 formed on the upper surface 2a of the circuit board 2. On the other hand, the low melting point solder bonding portion 42 is bonded to an electrode pad (hereinafter, referred to as element side pad) 33 formed on the lower surface 3a of the optical element silicon chip 3. The solder bump 4 is formed by integrally joining the high melting point solder bonding portion 41 and the low melting point solder bonding portion 42 by performing low temperature hierarchical bonding. Specifically, when reflowing the high melting point solder joint 41 and the low melting point solder joint 42, the reflow temperature is lower than the melting point of the high melting point solder joint 41 and higher than the melting point of the low melting point solder joint 42. By reflowing with, both are joined together. Further, a concavo-convex joint portion 43 having a concavo-convex shape is formed on the joint interface between the high-melting-point solder joint portion 41 and the low-melting-point solder joint portion 42 in the solder bump 4. Reference numerals 7 and 7A represent a mold resin and a second mold resin. The mold resin 7 and the second mold resin 7A will be described later.

0015&lt;&lt; Mounting method of semiconductor element &gt;&gt; Next, a method of mounting the optical element silicon chip 3 will be described. 2 to 11 are diagrams illustrating a mounting process of the optical element silicon chip 31.

0016When manufacturing the semiconductor device 1, the circuit board 2 shown in FIG. 2 is prepared. The circuit board 2 is, for example, a resin substrate formed of, for example, an epoxy resin or the like, but is not limited thereto. A plurality of substrate-side pads 23 are exposed and formed at appropriate positions on the upper surface 2a of the circuit board 2. Further, the circuit board 2 is formed with a light receiving unit 21 for receiving light output from the light emitting unit 31 of the optical element silicon chip 3, a waveguide 22, and the like.

0017Next, as shown in FIG. 3, a solder ball (hereinafter referred to as "high melting point solder ball") 41A formed of high melting point solder (high temperature solder) such as SnAgCu type solder (tin-silver-copper type solder) is used. , Attach to each board side pad 23 of the circuit board 2. The high melting point solder ball 41A forms the high melting point solder joint 41 of the solder bump 4 shown in FIG. 1 after the optical element silicon chip 3 is mounted on the circuit board 2. To the substrate side pad 23 of the refractory solder ball 41A The installation can be performed by the following procedure. First, the flux is supplied onto the substrate side pad 23. The flux may be supplied onto the substrate-side pad 23 by squeezing using a printing device. After the application of the flux to the substrate side pad 23 is completed, the high melting point solder ball 41A is mounted on the flux and heated (reflow) by the reflow furnace. The reflow temperature here may be a temperature higher than the melting temperature of the refractory solder ball 41A (for example, about 235 ° C.). By performing the reflow, the high melting point solder balls 41A are melted, and the high melting point solder balls 41A are integrally joined to each substrate side pad 23. In the present embodiment, the high melting point solder ball 41A is an example of the first solder bonding material.

0018Next, a jig for forming a recess (hereinafter referred to as a jig for forming a recess) 6 as shown in FIG. 4 is prepared. The recess forming jig 6 is mounted on a semiconductor manufacturing apparatus (flip chip bonder) used for mounting the optical element silicon chip 3 on the circuit board 2, and is heated by receiving heat supply from the semiconductor manufacturing apparatus. A plurality of protrusions 61 are provided on the lower surface 6a of the recess forming jig 6 so as to correspond to the planar arrangement pattern of the solder balls 41. In the present embodiment, the protrusion 61 has a substantially conical shape, but the shape of the protrusion 61 can be changed as appropriate. Further, a flat flat portion 62 is formed on a portion of the lower surface 6a of the recess forming jig 6 where the protrusion 61 is not formed. In the present embodiment, the recess forming jig 6 is formed of a glass plate. However, the recess forming jig 6 may be formed by using another material.

0019Next, as shown in FIG. 5, the recess forming jig 6 is pressed against the crown 410 of the refractory solder ball 41A. As described above, each protrusion 61 formed on the lower surface 6a of the recess forming jig 6 is arranged in association with the plane arrangement pattern of the refractory solder ball 41A attached to the circuit board 2. Here, the recess forming jig 6 is pressed against the refractory solder ball 41A so that each protrusion 61 of the recess forming jig 6 bites into the crown 410 of the corresponding refractory solder ball 41A.

0020In the present embodiment, the recess forming jig 6 is pressed against the crown 410 of the high melting point solder ball 41A while being heated to, for example, about 150 to 180 ° C. As a result, the high melting point solder ball 41A is softened by the heat transferred from the recess forming jig 6, so that the stress acting on the high melting point solder ball 41A is reduced, and the protrusion 61 is formed on the crown 410 of the high melting point solder ball 41A. Can be made to bite. As a result, as shown in FIG. 5, a conical concave portion 411 (concave and convex shape) corresponding to the protrusion 61 is formed on the crown portion 410 of the refractory solder ball 41A (recess formation step). In the present embodiment, a single recess 411 is formed for the crown 410 of each melting point solder ball 41A, but a plurality of recesses 411 are formed in one melting point solder ball 41A. May be done. Further, the height of the protrusion 61 in the recess forming jig 6 can be appropriately changed according to the depth of the recess 411 formed in the refractory solder ball 41A.

0021Next, as shown in FIG. 6, a mold resin 7 as a sealing material is supplied onto the circuit board 2 in a state where the recess forming jig 6 is pressed against the crown 410 of the high melting point solder ball 41A. Then, the high melting point solder ball 41A is sealed so that at least the crown 410 of the high melting point solder ball 41A is exposed (sealing step). In this embodiment, a thermoplastic resin is used as the mold resin 7. As the thermoplastic resin, for example, a thermoplastic epoxy resin can be preferably used.

0022In the sealing step, for example, the mold resin 7 in a softened state by heating to about 80 ° C. is poured into the upper surface 2a of the circuit board 2. At that time, since the recess forming jig 6 is left on the crown portion 410 of the high melting point solder ball 41A, it is possible to prevent the mold resin 7 from covering the crown portion 410 of the high melting point solder ball 41A. That is, by performing the sealing process in a state where the recess forming jig 6 is pressed against the crown 410 of the high melting point solder ball 41A, the molding process is performed. It is possible to prevent the recess 411 from being covered with the resin 7. As described above, in the present embodiment, the periphery of the high melting point solder ball 41A is covered with the mold resin 7, leaving the crown 410 of the high melting point solder ball 41A. Then, after the mold resin 7 is cooled and cured, the recess forming jig 6 is removed from the high melting point solder ball 41A.

0023As described above, the flat portion 62 is formed on the lower surface 6a of the recess forming jig 6. Therefore, by performing the sealing step with the recess forming jig 6 attached to the crown 410 of the high melting point solder ball 41A, the upper surface of the mold resin 7 is flattened by the flat portion 62 of the recess forming jig 6. Can be done (flattening process). Therefore, as shown in FIG. 7, when the recess forming jig 6 is removed from the refractory solder ball 41A, the recess 411 is formed on the crown 410 of the recess forming jig 6, and the outer peripheral edge of the recess 411 is formed. The flattened flat surfaces 71 of the mold resin 7 are arranged in a row in the portion.

0024Next, as shown in FIG. 8, the screen slab 8 having the through hole 8a formed at a predetermined position is placed on the circuit board 2. The screen plate 8 is installed on the flat surface 71 of the mold resin 7 as shown. In the screen plate 8, a plurality of through holes 8a are formed at positions corresponding to the planar arrangement pattern of the refractory solder balls 41A. When the screen plate 8 is installed on the circuit board 2, the positions of the through holes 8a are aligned with the positions of the corresponding high melting point solder balls 41A (recesses 411).

0025Next, as shown in FIG. 9, a low melting point solder paste 42A formed from, for example, SnBi-based solder (tin-bismuth-based solder) or the like is supplied onto the screen plate 8 using, for example, a printing apparatus. The low melting point solder paste 42A forms the low melting point solder joint 42 of the solder bump 4 shown in FIG. 1 after the optical element silicon chip 3 is mounted on the circuit board 2. The low melting point solder paste 42A supplied by the printing apparatus is filled into the recess 411 of the high melting point solder ball 41A through each through hole 8a by, for example, squeezing with a squeegee. The melting point of the low melting point solder paste 42A is about 139 ° C, which is lower than the melting point of the high melting point solder ball 41A (about 220 ° C). In the present embodiment, the low melting point solder paste 42A is an example of the second solder bonding material.

0026When the low melting point solder paste 42A is supplied, the gap between the high melting point solder balls 41A is already covered with the mold resin 7. Therefore, even if a force acts in the direction in which the screen plate 8 causes a relative displacement in the plane direction due to squeezing using a squeegee, the high melting point solder ball 41A or the high melting point solder ball 41A is joined to the substrate side pad 23. The stress acting on the part can be reduced. As a result, it is possible to suppress the occurrence of damage such as cracks at the high melting point solder ball 41A and the joint portion between the high melting point solder ball 41A and the substrate side pad 23.

0027Further, since the screen plate 8 can be installed on the flat surface 71 of the mold resin 7, the low melting point solder paste 42A can be printed with high accuracy even if the adjustment accuracy of the squeegee is relatively rough. Work efficiency can be improved. Further, by coating the periphery of the high melting point solder ball 41A with the mold resin 7, the low melting point solder paste 42A flowing into the through hole 8a of the screen plate 8 leaks from the gap between the through hole 8a and the high melting point solder ball 41A. It is suppressed to put out. As a result, an appropriate amount of the low melting point solder paste 42A can be accurately supplied on the high melting point solder ball 41A. Further, since the low melting point solder paste 42A can be suppressed from slipping off from the high melting point solder ball 41A, a short circuit between adjacent substrate side pads 23 can be suppressed.

0028Next, the screen plate 8 is removed from the circuit board 2, and as shown in FIG. 10, the optical element silicon chip 3 so that the lower surface 3a of the optical element silicon chip 3 faces the upper surface 2a of the circuit board 2. To place. A plurality of element-side pads 33 are exposed and formed at appropriate positions on the lower surface 3a of the optical element silicon chip 3. Further, a light emitting unit 31 and a waveguide 32 are formed in the optical element silicon chip 3. In the optical element silicon chip 3, the plane positions of the element side pad 33 and the substrate side pad 23 match, and a predetermined bonding gap Gc is provided between the circuit board 2 and the optical element silicon chip 3. The relative position with the circuit board 2 is adjusted.

0029Next, the circuit board 2 and the optical element silicon chip 3 are heat-treated (reflow) by the reflow furnace (reflow step). Here, the reflow temperature (heating temperature) at the time of performing reflow is set to be lower than the melting point of the high melting point solder ball 41A and higher than the melting point of the low melting point solder paste 42A. For example, the reflow temperature is set to about 160 ° C. At the time of reflow, since the reflow temperature is lower than the melting point of the high melting point solder ball 41A, the high melting point solder ball 41A does not change its shape and maintains its original shape. On the other hand, since the reflow temperature is higher than the melting point of the low melting point solder paste 42A, the low melting point solder paste 42A will melt.

0030In the present embodiment, the dimension of the refractory solder ball 41A is set to be slightly smaller than the dimension obtained by subtracting the thicknesses of the substrate side pad 23 and the element side pad 33 from the bonding gap Gc. Then, the high melting point solder ball 41A whose shape does not change during reflow is used as a spacer (space securing member) for securing the joining gap Gc, and the gap between the element side pad 33 and the high melting point solder ball 41A is filled with the low melting point solder paste. It was decided to connect by 42A. The low melting point solder paste 42A melted by the reflow diffuses into the solder alloy of the high melting point solder ball 41A, and the low melting point solder paste 42A and the high melting point solder ball 41A are integrally joined. After that, the low melting point solder paste 42A and the high melting point solder ball 41A are cooled to complete the solder bump 4 shown in FIG. At that time, the above-mentioned low melting point solder paste 42A forms the low melting point solder joint portion 42 of the solder bump 4, and the high melting point solder ball 41A forms the high melting point solder joint portion 41 of the solder bump 4.

0031After that, as shown in FIG. 11, the gap between the mold resin 7 and the optical element silicon chip 3 is filled with the second mold resin 7A. As the second mold resin 7A, a thermosetting resin that softens at a temperature lower than the melting point of the low melting point solder 42 can be preferably used. Through the above steps, the mounting process of the optical element silicon chip 3 on the circuit board 2 is completed, and the semiconductor device 1 is completed.

0032As described above, in the mounting method of the optical element silicon chip 3 according to the present embodiment, temperature layer bonding is performed at a temperature lower than the melting point of the high melting point solder ball 41A (high melting point solder joint portion 41). According to this, since the high melting point solder ball 41A that maintains its shape even during reflow can be used as a spacer, a large bonding gap Gc can be easily secured. Further, the gap between the element side pad 33 and the high melting point solder ball 41A in the optical element silicon chip 3 is filled with the low melting point solder paste 42A that melts during reflow. Therefore, even if the height of each high melting point solder ball 41A is slightly different or the optical element silicon chip 3 is slightly tilted, the variation (error) in the height direction can be easily eliminated by the low melting point solder paste 42A. Can be absorbed by. As a result, even if the design dimension of the junction gap Gc between the circuit board 2 and the optical element silicon chip 3 is large, the junction gap Gc can be accurately formed according to the design dimensions. That is, according to the mounting method according to the present embodiment, the dimensional accuracy of the joint gap Gc can be improved.

0033Further, in the mounting process of the optical element silicon chip 3 according to the present embodiment, the recess 411 is provided in the crown 410 of the refractory solder ball 41A (see FIG. 7 and the like). According to this, the boundary surface where the high melting point solder joint portion 41 (high melting point solder ball 41A) and the low melting point solder joint portion 42 (low melting point solder paste 42A) of the solder bump 4 are joined has an uneven shape. The joint 43 can be formed. In this way, by forming the concavo-convex joint portion 43 on the joint interface between the high melting point solder joint portion 41 and the low melting point solder joint portion 42, the high melting point solder joint portion 41 and the low melting point solder joint portion 42 are mechanically engaged with each other. By the action, the mechanical strength to resist the external force can be increased.

0034Further, by forming the joint interface between the high melting point solder joint portion 41 and the low melting point solder joint portion 42 into an uneven shape, the contact area between the high melting point solder joint portion 41 and the low melting point solder joint portion 42 can be increased. Therefore, it is possible to suppress the aggregation of the low melting point solder paste 42A during reflow, promote the diffusion of the low melting point solder paste 42A into the high melting point solder ball 41A, and promote the integration of both. .. As a result, interfacial peeling between dissimilar solder alloys is less likely to occur, and the mutual bonding strength can be increased.

0035As described above, according to the mounting method of the optical element silicon chip 3 according to the present embodiment, the bonding gap (bonding clearance) Gc between the optical element silicon chip 3 and the circuit board 2 is accurately controlled to an appropriate value. Can be done. Moreover, high bonding reliability can be ensured even if the reflow temperature is set relatively low when the optical element silicon chip 3 is mounted.

0036In the method for mounting the optical element silicon chip 3 described above, the sealing step with the mold resin 7 may be performed before forming the recess 411 in the crown 410 of the refractory solder ball 41A. Further, in some cases, the sealing step with the mold resin 7 can be omitted. Even when the sealing step is omitted, by forming the recess 411 in the crown 410 of the high melting point solder ball 41A, the low melting point solder paste 42A supplied from the printing apparatus can be received by the recess 411. As a result, the low melting point solder paste 42A can be prevented from slipping off from the high melting point solder ball 41A. As a result, an appropriate amount of the low melting point solder paste 42A can be supplied to the high melting point solder ball 41A, and the bonding reliability between the optical element silicon chip 3 and the circuit board 2 via the solder bump 4 is improved. Is possible.

0037Further, in the above-described method for mounting the optical element silicon chip 3, the flattening step of flattening the upper surface of the mold resin 7 is performed by using the lower surface 6a of the recess forming jig 6. According to this, the recess forming step and the flattening step of forming the recess 411 on the crown 410 of the refractory solder ball 41A can be performed at the same time. As a result, the man-hours required for mounting the optical element silicon chip 3 can be reduced, and the manufacturing efficiency of the semiconductor device 1 can be improved. However, the flattening step of flattening the upper surface of the mold resin 7 may be performed before supplying the paste of the low melting point solder 42 to the recess 411, or may be performed after the recess forming step.

0038&lt;&lt; Modification example of mounting method of semiconductor element &gt;&gt; Next, a modified example of the mounting method of the optical element silicon chip 3 will be described. 12 to 18 are views for explaining the mounting process of the optical element silicon chip 3 according to this modification. In the following, the differences from the mounting method described with reference to FIGS. 2 to 11 will be mainly described. Further, the same reference numerals will be given to the configurations common to the above-described embodiments, and detailed description thereof will be omitted.

0039The mounting method according to this modification is also the same as that of the above-described embodiment until the high melting point solder ball 41A is attached to each substrate side pad 23 of the circuit board 2. The melting point solder ball 41A is as described above. Next, as shown in FIG. 12, the mold resin 7 as a sealing material is supplied to the upper surface 2a of the circuit board 2 in which the refractory solder ball 41A is attached. The mold resin 7 is formed of a thermoplastic resin as described above. In this modification, the softened mold resin 7 is supplied so that the crown 410 of the high melting point solder ball 41A is at least exposed, and the high melting point solder ball 41A is sealed by the mold resin 7. (Seal process). The upper surface of the mold resin 7 supplied in the sealing step does not have to be flat.

0040Next, the screen plate 8A with protrusions shown in FIG. 13 is prepared. Similar to the screen plate 8 described above, the screen plate 8A with protrusions has a plurality of through holes 8a formed at positions corresponding to the arrangement pattern of the refractory solder balls 41A. Further, a plurality of protrusions 81 are formed on the lower surface 80 of the screen plate 8A with protrusions. Two protrusions 81 are provided in the vicinity of the peripheral edge of each through hole 8a in the lower surface 80 of the screen plate 8A with protrusions, and the protrusions 81 project downward from the lower surface 80. However, the number of protrusions 81 corresponding to each through hole 8a can be changed as appropriate. Further, on the lower surface of the screen plate 8A with protrusions, a flat flat portion 82 is formed on a portion where the protrusions 81 are not formed.

0041Next, as shown in FIG. 14, the screen plate 8A with protrusions is placed on the circuit board 2 while aligning the through holes 8a with the positions of the corresponding refractory solder balls 41A. Here, when the screen plate 8A with protrusions is placed on the circuit board 2, the protrusions 81 provided on the lower surface 80 of the screen plate 8A with protrusions are pressed against the crown 410 of the high melting point solder ball 41A to bite into the screen plate 8A. .. As a result, a recess 411A is formed in the crown 410 of each high melting point solder ball 41A. In this modification, since two protrusions 81 are provided on the periphery of each through hole 8a in the screen plate 8A with protrusions, two recesses 411A are formed in the crown 410 of each melting point solder ball 41A. (Recess formation process). In this modification, the recess forming step is performed before the mold resin 7 is cured. By pressing the flat portion 82 of the screen plate 8A with protrusions against the upper surface of the softened mold resin 7, the flat surface 71 can be formed on the upper surface of the mold resin 7. That is, the upper surface of the mold resin 7 can be flattened.

0042Here, the high melting point solder ball 41A is sealed with a mold resin 7 filled around the high melting point solder ball 41A. Therefore, when the protrusion 81 of the screen plate 8A with a protrusion is pressed against the crown 410 of the refractory solder ball 41A to form the recess 411A, a large stress acts on the joint between the refractory solder ball 41A and the substrate side pad 23. Can be suppressed. As described above, in this modification, the sealing step is performed before the recess forming step.

0043Next, as shown in FIG. 15, the low melting point solder paste 42A is supplied onto the projected screen plate 8A using, for example, a printing device. The low melting point solder paste 42A is as described above. The low melting point solder paste 42A supplied by the printing apparatus is supplied to the crown 410 of the high melting point solder ball 41A through each through hole 8a by squeezing with a squeegee.

0044Also in this modification, when the low melting point solder paste 42A is supplied to the crown 410 of the high melting point solder ball 41A, the periphery of the high melting point solder ball 41A is coated (sealed) with the mold resin 7. Therefore, it is possible to prevent the low melting point solder paste 42A from slipping off from the crown 410 of the high melting point solder ball 41A, and to transfer an appropriate amount of the low melting point solder paste 42A onto the high melting point solder ball 41A with high accuracy. Further, since the flat flat surface 71 is formed on the upper surface of the mold resin 7, the low melting point solder paste 42A can be printed with high accuracy. Further, when the low melting point solder paste 42A is supplied, the stress acting on the joint portion between the high melting point solder ball 41A and the substrate side pad 23 can be reduced, so that the breakage of the joint portion can be suppressed.

0045Next, the screen plate 8A with protrusions is removed from the circuit board 2. As a result, as shown in FIG. 16, the low melting point solder paste 42A filled in the through hole 8a of the screen plate 8A with protrusions flows into the recess 411A formed in the crown 410 of the high melting point solder ball 41A. It is filled. Next, as shown in FIG. 17, the optical element silicon chip 3 is arranged so that the lower surface 3a of the optical element silicon chip 3 faces the upper surface 2a of the circuit board 2. In the optical element silicon chip 3, the plane positions of the element side pad 33 and the substrate side pad 23 match, and a predetermined bonding gap Gc is provided between the circuit board 2 and the optical element silicon chip 3. The relative position with the circuit board 2 is adjusted.

0046Next, the circuit board 2 and the optical element silicon chip 3 are heat-treated (reflow) by the reflow furnace (reflow step). The reflow temperature is set to be lower than the melting point of the high melting point solder ball 41A and higher than the melting point of the low melting point solder paste 42A, as in the above embodiment. Therefore, similarly to the above embodiment, the low melting point solder paste 42A melts during the reflow, while the high melting point solder ball 41A maintains the shape before the reflow. Also in this modification, the dimension of the refractory solder ball 41A is set to be slightly smaller than the dimension obtained by subtracting the thicknesses of the substrate side pad 23 and the element side pad 33 from the bonding gap Gc. Then, the high melting point solder ball 41A whose shape does not change during reflow is used as a spacer for securing the joining gap Gc, and the gap between the element side pad 33 and the high melting point solder ball 41A is connected by the low melting point solder paste 42A. After that, the low melting point solder paste 42A and the high melting point solder ball 41A are cooled to form the solder bumps 4 as in the above embodiment. At that time, the low melting point solder paste 42A forms the low melting point solder joint portion 42 of the solder bump 4, and the high melting point solder ball 41A forms the high melting point solder joint portion 41 of the solder bump 4.

0047After that, as shown in FIG. 18, the gap between the mold resin 7 and the optical element silicon chip 3 is filled with the second mold resin 7A. As the second mold resin 7A, a thermosetting resin that softens at a temperature lower than the melting point of the low melting point solder 42 can be preferably used. Through the above steps, the mounting process of the optical element silicon chip 3 on the circuit board 2 is completed, and the semiconductor device 1 is completed.

0048Also in this modification, the recess 411A is provided in the crown 410 of the refractory solder ball 41A. According to this, the concavo-convex joint having an uneven shape on the boundary surface where the high melting point solder joint portion 41 (high melting point solder ball 41A) and the low melting point solder joint portion 42 (low melting point solder paste 42A) of the solder bump 4 are joined. Part 43 is formed. As a result, the mechanical strength against the external force of the solder bump 4 can be increased by the mechanical meshing action between the high melting point solder joint 41 and the low melting point solder joint 42. Then, the contact area between the high melting point solder joint 41 and the low melting point solder joint 42 can be increased by the uneven joint 43 having the uneven shape. Therefore, interfacial peeling between dissimilar solder alloys is less likely to occur, and the bonding strength between the high melting point solder bonding portion 41 and the low melting point solder bonding portion 42 can be increased. As a result, excellent bonding (connection) reliability of the circuit board 2 and the optical element silicon chip 3 via the solder bump 4 can be realized. Then, by performing temperature hierarchical bonding in which the reflow temperature is lower than the melting point of the high melting point solder ball 41A (high melting point solder joint portion 41), a larger bonding gap Gc can be easily obtained, and moreover, the bonding is performed. The dimensional accuracy of the gap Gc can be improved more than before. That is, even if the design dimension of the junction gap Gc between the circuit board 2 and the optical element silicon chip 3 is large, the dimensional accuracy of the junction gap Gc to be formed can be suitably improved.

0049Further, in the mounting method according to this modification, the low melting point solder paste 42A is transferred to the crown 410 of the high melting point solder ball 41A by using the projection screen plate 8A having the protrusion 81 and the flat portion 82. .. According to this, the transfer of the low melting point solder paste 42A to the crown 410 of the high melting point solder ball 41A, the formation of the recess 411A on the crown 410 of the high melting point solder ball 41A, and the flattening of the upper surface of the mold resin 7 are performed. , Can be done collectively (in the same process). As a result, the man-hours required for mounting the optical element silicon chip 3 can be reduced. Therefore, the manufacturing efficiency of the semiconductor device 1 can be improved.

0050Further, this modification is different from the above embodiment in that a recess 411A is formed in the crown 410 of the refractory solder ball 41A in a state where the periphery of the refractory solder ball 41A is sealed with the mold resin 7. .. According to this, when the protrusion 81 of the screen plate 8A with protrusion is pressed against the crown 410 of the high melting point solder ball 41A, the stress acting on the joint between the high melting point solder ball 41A and the substrate side pad 23 is suitably reduced. can do. As a result, the joint portion between the high melting point solder ball 41A and the substrate side pad 23 can be made more difficult to be damaged.

0051Although the method of mounting the semiconductor device and the semiconductor element according to the present case has been described above according to the embodiment, the present case is not limited to these. It is obvious to those skilled in the art that various changes, improvements, combinations and the like can be made to the above embodiments. For example, in the above-described embodiment and modification, the case where the semiconductor element mounted on the circuit board 2 is a light emitting element such as a VCSEL has been exemplified, but a light receiving element such as a photodiode may be used. Further, the mounting method according to the present invention can be suitably applied when mounting various semiconductor devices, not limited to optical elements such as VCSELs and photodiodes.

00521 ... Semiconductor device 2 ... Circuit board 3 Optical element Silicon chip 4 Solder bump 6 Jig for forming recesses 7 Mold resin 23 Board side pad 33 Element side pad 41 High melting point solder joint 41A High melting point solder ball 42 Low melting point solder joint 42A Low melting point solder paste 43 Concavo-convex joint 410 Top of the head 411 Recess Gc Joint gap