JP2014187137A - Method for producing electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the separation of wire due to heating after wire bonding as much as possible in a method for producing an electronic device which is formed by wire-bonding and soldering to a power chip provided with a wire pad composed of an Au-plated layer on an undercoat whose surface is a Ni-plated layer and a solder land for soldering.SOLUTION: The method for producing an electronic device comprises a soldering step of soldering a terminal 50, a wire-bonding step of joining a wire 40 to a wire pad 21 thereafter, a heating step of heating a power chip 20 thereafter. Then, a Ni diffusion step in which Ni is diffused from a Ni-plated layer 211 to the surface of an Au-plated layer 212 in the wire pad 21 is carried out by heating the prepared power chip 20 before the soldering step.

Description

  The present invention relates to a method for manufacturing an electronic device having an electronic component having both wire pads and solder lands.

  2. Description of the Related Art Conventionally, an electronic device is generally known that includes an electronic component having a wire pad for wire bonding and a wire made of aluminum wire-bonded on the wire pad. Here, the wire pad is usually composed of an Au plating layer whose surface is a Ni plating layer, that is, a Ni / Au plating layer.

  In such a case, for the electronic device after wire bonding, for example, heating for further connection of other components, application of an adhesion imparting agent before mold sealing, drying, etc. is performed as a post-process. It is normal.

  Therefore, for example, as described in Patent Document 1, when the Au plating layer is thick (for example, 500 nm or more), the electronic component becomes high temperature (for example, 150 ° C. or more) by the heating process, and voids are generated in the Au plating layer. It is known that the bonding wire is easily peeled off.

JP 2003-59962 A

  On the other hand, this inventor confirmed experimentally that the void generation | occurrence | production in the said Au plating layer can be suppressed by making Au plating layer thin, for example with 20 nm-50 nm.

  Furthermore, the present inventor has studied the case where the electronic component has a configuration in which a solder land for soldering with a solder containing Sn is further added to the wire pad. Hereinafter, this configuration is referred to as a “wire-solder dual configuration”.

  This wire-solder dual arrangement is usually formed by performing wire bonding after soldering. As a result of the study by the present inventor, in this case, it was found that even if the Au plating layer was made thin, peeling of the wire occurred due to heating to the electronic device described above.

  The present invention has been made in view of the above problems, and wire bonding and soldering are performed on an electronic component including a wire pad made of an Au plating layer whose surface is a Ni plating layer and a solder land for soldering. In the manufacturing method of the electronic device formed by performing the above, the object is to prevent wire peeling due to heating after wire bonding as much as possible.

  In order to achieve the above object, the present inventor has intensively studied and estimated the occurrence mechanism of the wire peeling in the electronic device having both the wire-solder configuration as follows. This estimation mechanism will be described with reference to FIG. FIG. 7 shows a schematic cross section of the wire pad 21 whose surface is made of the Au plating layer 212 with the Ni plating layer 211 as a base.

  First, before wire bonding, a solder land (not shown) on the electronic component is soldered with solder containing Sn. Then, as shown in FIGS. 7A and 7B, Sn1 (indicated by a dot-hatched circle in the figure) is scattered from the solder on the electronic component onto the wire pad 21 by the reflow of the solder. Then, it adheres to the surface of the Au plating layer 212.

Further, this Sn1 diffuses into the Au plating layer 212 due to the heat of the solder reflow, reacts with Ni diffused from the underlying Ni plating layer 211, and as shown in FIG. 7C, the Au plating layer An Sn—Ni alloy (for example, Ni ₃ Sn, indicated by a hatched circle on one side in the figure) 2 is formed in 212.

  Then, by performing wire bonding to the wire pad 21 in this state, the wire 40 made of Al is connected on the Au plating layer 212 as shown in FIG. After the wire bonding, the electronic device is heated as a post-process described above.

  At this time, in the heating step, as shown in FIGS. 7E and 7F, mutual diffusion occurs between the Au of the Au plating layer 212 and the Al of the wire 40 in the wire pad 21, and the Ni plating layer 211 and the wire 40, the Au—Al alloy layer 213 is formed, and the thin Au plating layer 212 substantially disappears.

  However, in the formation of the Au—Al alloy layer 213, if the Sn—Ni alloy 2 exists in the Au plating layer 212, the diffusion of Au is obstructed by the Si—Ni alloy 2, and the existing portion of the Sn—Ni alloy 2 is present. In this case, the diffusion is slow and the diffusion is fast in the non-existing portion, so that the diffusion rate of Au becomes non-uniform. Therefore, as shown in FIGS. 7E and 7F, void B is generated in the portion of the Sn—Ni alloy 2 in the wire pad 21.

  Therefore, the strength of the wire pad 21 is reduced at the void B portion, and the wire 40 is easily peeled off. The above is the presumed mechanism by examination of this inventor. This is confirmed by microscopic observation and elemental analysis.

  Therefore, in view of this mechanism, the present inventor can prevent Sn adhering to the Au plating layer surface of the wire pad from diffusing into the Au plating layer at the time of the solder reflow. It was thought that the formation of the Ni alloy could be prevented as much as possible. The present invention has been created by focusing on this point.

That is, according to the first aspect of the present invention, an electronic component (20) having a wire pad (21) for wire bonding and a solder land (22) for soldering, and a wire made of aluminum wire-bonded to the wire pad (40) and a joining member (50) soldered to a solder land via a solder (70) containing Sn,
As an electronic component, a preparation process for preparing the surface of the wire pad consisting of an Au plating layer (212) with the Ni plating layer (211) as a base, solder is disposed on the solder land, and a joining member is provided on the solder After reflowing the solder in the mounted state, a soldering process for soldering the joining member, a wire bonding process for bonding the wire to the wire pad by performing wire bonding after the soldering process, and after the wire bonding process A heating process for heating the electronic component,
Before the soldering step, the prepared electronic component is heated to perform a Ni diffusion step of diffusing Ni from the Ni plating layer on the surface of the Au plating layer in the wire pad.

  According to this, since Ni is diffused in advance on the surface of the Au plating layer by the Ni diffusion step before the solder reflow, even if Sn (1) adheres to the surface of the Au plating layer during the solder reflow, the Au plating of this Sn Diffusion into the layer is inhibited by Ni (3) present on the same surface.

  Therefore, since the formation of the Sn—Ni alloy (2) is suppressed in the Au plating layer, the Au—Al alloy layer (213) is formed between the Ni plating layer and the Al wire by heating after wire bonding. Even if formed, generation of voids (B) in the wire pad can be suppressed. Therefore, according to the present invention, it is possible to prevent wire peeling due to heating after wire bonding as much as possible.

  According to a second aspect of the present invention, in the method of manufacturing an electronic device according to the first aspect, in the soldering step, the solder is disposed on the solder land as a solder paste containing a flux. In particular, in the case of a solder paste, since there is much adhesion of Sn, the effect by the Ni diffusion step is effectively exhibited.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

(A) is a schematic sectional drawing of the electronic device concerning embodiment of this invention, (b) is an enlarged view which shows the detail of the wire pad and solder land immediately after the wire bonding in the electronic component in (a). (C) is a figure which shows the state after the heating performed after the wire bonding in (b). It is process drawing which shows the manufacturing method of the electronic device shown by FIG. It is a schematic sectional drawing which shows the state change of the wire pad accompanying progress of the manufacturing process shown by FIG. It is a figure which shows the presumed mechanism of wire peeling generation | occurrence | production prevention in the said embodiment. It is a figure which shows an example of the effect in the said embodiment. It is a figure which shows an example of the effect in the said embodiment. It is a figure which shows the presumed mechanism of wire peeling generation | occurrence | production by the inventor's trial manufacture examination.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
The electronic device S1 according to the first embodiment of the present invention will be described with reference to FIGS. The electronic device S1 is mounted on a vehicle such as an automobile and is applied as a device for driving, controlling, etc. various devices for the vehicle.

  The electronic device S1 of the present embodiment is broadly divided into a substrate 10, a power chip 20 and other mounted components 30 mounted on the substrate 10, and each of the substrate 10, each component 20, 30 on the substrate 10. A bonding wire 40 and a terminal 50 that are electrically connected to each other are provided.

  The substrate 10 has a plate shape in which the front and back plate surfaces are one surface 11 and the other surface 12, respectively. The substrate 10 of the present embodiment is a lead frame made of Cu or the like, but other examples of the substrate 10 include a ceramic substrate and a printed circuit board. In FIG. 1, a cross section of the electronic device S <b> 1 along the thickness direction of the substrate 10 is shown.

  The power chip 20 is configured as an electronic component 20 having wire pads 21 for wire bonding and solder lands 22 for soldering. Examples of such a power chip 20 include a power MOS transistor and an IGBT.

  The other mounted component 30 is a control IC such as a microcomputer. The power chip 20 and other mounting components 30 are connected to the one surface 11 of the substrate 10 via a mounting material 60 such as solder or a conductive adhesive.

  The wire pad 21 and the solder land 22 in the power chip 20 have aluminum layers 210 and 220 made of aluminum (Al) on the one surface 11 side of the substrate 10, and each layer is laminated thereon.

  Here, as shown in FIG. 1B and FIG. 2B to be described later, the surfaces of both the wire pad 21 immediately after the bonding wire 40 and the solder land 22 before the solder 70 are connected are as follows. It consists of Au plating layers 212 and 222 with Ni plating layers 211 and 221 as bases. Although not limited, the thickness of the Au plating layers 212 and 222 is, for example, about 20 nm to 50 nm.

  That is, both the wire pad 21 and the solder land 22 are initially made of “Ni / Au plating”. Then, by heating the wire pad 21 after the bonding wire 40 is connected and soldering to the solder land 22, as shown in FIGS. 1B and 1C, surface portions of the wire pad 21 and the solder land 22. Changes from the initial state, and finally becomes the state of FIG.

  Including this state change, each connection configuration of the wire pad 21 and the solder land 22 will be described. The bonding wire 40 is made of Al and is formed by a normal wire bonding method. With this wire 40, the wire pad 21 of the power chip 20 and the other mounting component 30 are connected, and these are electrically connected.

  Immediately after the bonding wire 40 is connected to the wire pad 21, the surface of the wire pad 21 is initially “Ni / Au plated” as shown in FIG.

  Here, after wire bonding, for example, mounting of another component on the substrate 10, application of an adhesion-imparting agent before mold sealing, heating for drying, etc., or electronic component S 1 and other members A heating process as a post-process of wire bonding, such as connection, is performed.

  Then, the Au plating layer 212 on the surface of the wire pad 21 and the aluminum of the wire 40 are diffused by the heating process as a subsequent process, so that the thin Au plating layer 212 substantially disappears, and FIG. ), An Au—Al alloy layer 213 is formed.

  That is, finally (that is, when used as a product), the wire pad 21 in the electronic device S1 of the present embodiment includes the aluminum layer 210, the Ni plating layer 211, and the Au as shown in FIG. The Al alloy layer 213 is sequentially stacked from the substrate 10 side.

  On the other hand, the terminal 50 as a joining member to be soldered to the solder land 22 is made of Cu, iron-based metal, or the like, and has a plate shape bent as shown in FIG. With this terminal 50, the solder land 22 of the power chip 20 and the substrate 10 are soldered via the solder 70, and these are electrically connected. Here, the solder 70 is a lead-free solder or eutectic solder containing Sn (tin).

  By the soldering of the terminal 50, the Au plating layer 222 (see FIG. 2B) originally present on the surface of the solder land 22 is absorbed by the solder 70 and disappears. Finally, the solder land 22 in the electronic device S1 of the present embodiment has an aluminum layer 220 and a Ni plating layer 221 as shown in FIGS. 1B and 1C sequentially stacked from the substrate 10 side. It becomes the composition which was done.

  Next, a method for manufacturing the electronic device S1 of the present embodiment will be described with reference to FIG. In FIG. 2, the initial state of the wire pad 21 and the solder land 22 is shown in detail in (b), but the state change accompanying the manufacturing process of these parts 21 and 22 is as described above. , (C) and (d), the wire pads 21 and the solder lands 22 are simplified.

  First, in the preparation step, the substrate 10 is prepared as shown in FIGS. 2 (a) and 2 (b). Further, as an electronic component, a power chip 20 is prepared in which the surface of the wire pad 21 is made of an Au plating layer 212 with a Ni plating layer 211 as a base, that is, the “Ni / Au plating”.

  Here, the surface of the solder land 22 in the prepared power chip 20 is also the above-mentioned “Ni / Au plating”. Such wire pads 21 and solder lands 22 are formed by aluminum deposition, sputtering, electroplating, electroless plating, or the like. This is the preparation process.

  Next, as shown in FIG. 2B, the power chip 20 and other mounting components 30 are mounted and bonded to the one surface 11 of the substrate 10 via the mounting material 60 (component mounting step).

  Next, in the soldering process shown in FIG. 2C, the solder 70 is disposed on the solder land 22, and the solder 70 is reflowed in a state where the terminal 50 as a joining member is mounted on the solder 70. The terminal 50 is soldered. In the present embodiment, the solder 70 is applied by printing or the like in a solder paste state.

  After this soldering step, as shown in FIG. 2D, a wire bonding step of bonding the wire 40 to the wire pad 21 by performing aluminum wire bonding is performed.

  Thereafter, if necessary, a process of mounting other components on the substrate 10, an application of an adhesion imparting agent (primer) such as polyamide, a drying process, and other members when sealing with mold resin A heating process as a post-process such as a connecting process is performed. The electronic component is heated by a heating process as a subsequent process. Thus, the electronic device S1 is completed.

  In such a manufacturing method, in the present embodiment, the prepared power chip 20 is further heated before the soldering step, whereby the Ni plating layer 211 to the Ni plating layer 211 are formed on the surface of the Au plating layer 212 in the wire pad 21. A Ni diffusion step for diffusing is performed.

  The Ni diffusion step may be performed by heating the prepared power chip 20 alone, or may be performed by heating the component mounted on the substrate 10 in the component mounting step. The heating conditions of the power chip at this time are, for example, 280 ° C. or higher and 180 seconds or longer.

  As described above, in the manufacturing method of the present embodiment, the Ni diffusion process is performed before the soldering process, which is performed in order to suppress the peeling of the wire 40 due to the heating process as the subsequent process described above. is there. The Ni diffusion process will be specifically described with reference to FIGS. In addition, about the state change and mechanism of a wire pad shown by FIG. 3, FIG. 4, it is based on the result confirmed by microscope observation, elemental analysis, etc. FIG.

  Before the Ni diffusion step, as shown in FIGS. 3A and 4A, the surface of the wire pad 21 is composed of the underlying Ni plating layer 211 and the Au plating layer 212 thereon. Then, a Ni diffusion process is performed.

  Due to the heating in the Ni diffusion step, as shown in FIGS. 3B and 4A, Ni3 (shown by white circles in the figure) in the underlying Ni plating layer 211 becomes the surface of the Au plating layer 212. To spread. Then, when the soldering process is performed in this state, Sn1 (indicated by a dot-hatched circle in the figure) scatters from the solder on the solder land onto the wire pad 21 due to the heat of the solder reflow. It adheres to the surface of 212.

  Here, Sn1 adhering to the Au plating layer 212 due to the heat of solder reflow attempts to diffuse into the Au plating layer 212, but is blocked by Ni3 already present on the surface of the same Au plating layer 212. Therefore, diffusion of the Sn1 into the Au plating 212 layer is suppressed (see FIG. 4B). Therefore, in this embodiment, as shown in FIG. 4C, the formation of the Sn—Ni alloy 2 in the Au plating layer 212 is suppressed as much as possible.

  3 (c) and 4 (d), wire bonding is performed on the wire pad 21 in this state, so that the bonding wire 40 made of Al is formed on the Au plating layer 212. Connected.

  After the wire bonding, the electronic device S1 is heated as described above. At this time, in the heating process, as shown in FIGS. 3D, 4E, and 4F, mutual diffusion occurs between the Au of the Au plating layer 212 and the Al of the wire 40 in the wire pad 21. As a result, an Au—Al alloy layer 213 is formed between the Ni plating layer 211 and the wire 40.

  Here, in the formation of the Au—Al alloy layer 213 of the present embodiment, the amount of the Sn—Ni alloy 2 present in the Au plating layer 212 and hindering the mutual diffusion is greatly reduced. The non-uniformity of Au diffusion rate as described in (1) is eliminated as much as possible. Therefore, generation of void B generated in the wire pad 21 can be greatly suppressed.

  Thus, according to the present embodiment, even if the Au—Al alloy layer 213 is formed between the Ni plating layer 211 and the Al wire 40 in the heating process as a post process, Generation of void B can be suppressed. Therefore, according to this embodiment, it is possible to prevent wire peeling due to heating after wire bonding as much as possible.

  In the present embodiment, in the soldering process, the solder 70 is disposed on the solder land 22 as a solder paste containing flux. In the case of the solder paste, since the adhesion of Sn becomes remarkable, the effect by the Ni diffusion step is effectively exhibited.

  Here, a specific example of the above-described effect according to the present embodiment will be described with reference to FIGS. FIG. 5 shows experimentally confirmed effects of Ni diffusing to the surface of the Au plating layer 212 of the wire pad 21 by the Ni diffusion process.

  Specifically, etching was performed in the thickness direction from the surface of the Au plating layer 212 after the Ni diffusion step, and the Ni abundance at each etching depth was obtained by Auger Electron Spectroscopy (AES). In FIG. 5, the vertical axis represents the etching time (unit: minutes) and corresponds to the thickness direction of the Au plating layer 212, and the horizontal axis represents Ni strength and corresponds to the amount of Ni present.

  As shown in FIG. 5, the etching time is 0, that is, the amount of Ni present on the surface of the Au plating layer 212 is approximately doubled when “Yes” is present when the Ni diffusion step is performed and when the Ni diffusion step is not performed. is increasing. That is, the Ni diffusion effect by the Ni diffusion process in this embodiment was confirmed.

  FIG. 6 shows the results of examining the effect of preventing void generation by the annealing time (heating time, unit: second) at a heating temperature of 280 ° C. in the Ni diffusion step. According to FIG. 6, the heating time is approximately 180 seconds or more, and the degree of reduction in the void ratio is saturated. For this reason, in order to appropriately exhibit the Ni diffusion effect by the Ni diffusion step, when the heating temperature is 280 ° C., it is desirable to heat for 180 seconds or more.

(Other embodiments)
The electronic component 20 is not limited to the power chip 20 as long as it has both the wire pad 21 to which the Al wire 40 is wire-bonded and the solder land 22. For example, as other electronic components, various surface mount components, circuit boards, various sensor chips, and the like may be used.

  Moreover, as for the electronic component 20, the surface of the solder land 22 has the same “Ni / Au plating” configuration as that of the wire pad 21, but this is because the surface of the solder land 22 is formed in the manufacturing process of the electronic component. In the case of Au / Ni plating, the wire pad 21 is usually of the same surface configuration.

  However, the solder land 22 only needs to be soldered with the Sn solder 70. If the solder land 22 can be soldered, the same surface configuration as that of the wire pad 21 as in the above embodiment, that is, “Ni / Au It may be other than “plating”.

  Further, a plurality of electronic components 20 having both wire pads 21 and solder lands 22 may be mounted on the substrate 10. Also in this case, the Ni diffusion process may be performed on each electronic component 20 before the soldering process.

  Moreover, as a joining member, what is soldered to a solder land is sufficient, and things other than the said terminal 50 may be sufficient. Further, the solder 70 may be arranged by solder balls or the like in addition to the application of the solder paste.

  Further, the present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope described in the claims. Moreover, the said embodiment is not limited to said example of illustration. Further, in the above-described embodiment, it is needless to say that elements constituting the embodiment are not necessarily indispensable except for the case where it is clearly indicated that the element is essential and the case where the element is clearly considered to be essential in principle. . Further, in the above embodiment, when numerical values such as the number, numerical value, quantity, range, etc. of the constituent elements of the embodiment are mentioned, it is particularly limited to a specific number when clearly indicated as essential and in principle. The number is not limited to a specific number except for cases. In the above embodiment, when referring to the shape, positional relationship, etc. of components, the shape, position, etc., unless otherwise specified and in principle limited to a specific shape, positional relationship, etc. It is not limited to relationships.

DESCRIPTION OF SYMBOLS 10 Board | substrate 20 Power chip as an electronic component 21 Wire pad 22 Solder land 40 Bonding wire 50 Terminal as a joining member 70 Solder 211 Ni plating layer of wire pad 212 Au plating layer of wire pad

Claims (3)

An electronic component (20) having a wire pad (21) for wire bonding and a solder land (22) for soldering;
A wire (40) made of aluminum wire-bonded to the wire pad;
A joining member (50) soldered to the solder land via a solder (70) containing Sn, and an electronic device manufacturing method comprising:
A preparation step of preparing an electronic component having a surface of the wire pad made of an Au plating layer (212) based on a Ni plating layer (211);
A soldering step of soldering the joining member by placing the solder on the solder land and reflowing the solder in a state where the joining member is mounted on the solder;
After the soldering step, wire bonding is performed to bond the wire to the wire pad by performing wire bonding;
A heating step of heating the electronic component after the wire bonding step,
Before the soldering step, performing the Ni diffusion step of diffusing Ni from the Ni plating layer on the surface of the Au plating layer in the wire pad by heating the prepared electronic component. A method for manufacturing an electronic device.   2. The method of manufacturing an electronic device according to claim 1, wherein in the soldering step, the solder is disposed on the solder land as a solder paste containing a flux.   In the preparation step, as the electronic component, the surface of the solder land is also made of an Au plating layer (222) based on a Ni plating layer (221) using the same material as the wire pad. The method for manufacturing an electronic device according to claim 1, wherein:

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