JP2003133474A - Mounting structure of electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that the external connection pad of an electronic device is stripped from a solder connecting the pad with an external electric circuit board and thereby an electronic component cannot be operated normally over a long term. SOLUTION: An alloy layer 19 containing copper, nickel, and tin is formed on a nickel plating layer 17 covering the external connection pad 15 of an electronic device 1. The nickel plating layer 17 is bonded rigidly to a solder through the alloy layer 19 containing copper, nickel, and tin.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device comprising an electronic component such as a semiconductor element mounted on an insulating substrate having external connection pads covered on its lower surface with a nickel layer. The present invention relates to a mounting structure of an electronic device in which the device is mounted on an external electric circuit board having an electronic device connection pad on an upper surface via a solder containing tin. 2. Description of the Related Art Conventionally, an insulating substrate formed by laminating a plurality of insulating layers made of, for example, an epoxy resin or an insulating plate made of a glass-epoxy plate or the like, and a plurality of insulating films made of a copper foil or the like on the upper and lower surfaces. 2. Description of the Related Art An electronic device in which a wiring conductor is provided and an electronic component such as a semiconductor element is mounted on the insulating base is known. In such an electronic device, an electrode of an electronic component is electrically connected to a part of a wiring conductor led out on the insulating base via a bonding wire or a metal bump, and is connected to a lower surface of the insulating base. Some of the wiring conductors form external connection pads that are connected to the external electric circuit board via solder. Further, solder made of, for example, a lead-tin eutectic alloy is previously bonded to the external connection pad in order to facilitate connection with an external electric circuit board via solder. In order to bond the solder to the external connection pad in such an electronic device, a nickel plating layer having a thickness of about 0.5 to 10 μm and a gold plating having a thickness of about 0.01 to 0.8 μm are formed on the exposed surface of the external connection pad. A method is adopted in which the layers are sequentially applied, and the solder is melted and applied thereon. At this time, the gold plating layer is diffused and absorbed in the molten solder and disappears, and nickel on the nickel plating layer reacts with tin in the solder to form a nickel-tin alloy layer on the nickel plating layer. Is done. [0005] The electronic device is mounted on the external electric circuit board by fusing the solder joined to the external connection pad to the electronic device connection pad provided on the external electric circuit board. The electronic device connection pad may be formed by depositing a nickel plating layer on a copper foil or may be formed only of a copper foil. At this time, if the electronic device connection pad of the external electric circuit board is formed by depositing a nickel plating layer on a copper foil, the nickel-tin alloy layer on the nickel plating layer on the external connection pad of the electronic device Remains substantially as it is, and when the wiring is made of copper foil, the copper contained in the copper foil of the electronic device connection pad diffuses into the solder and reacts with the nickel-tin alloy layer on the external connection pad of the electronic device. By doing so, a copper-nickel-tin alloy layer is formed on the nickel-tin alloy layer on the external connection pads of the electronic device. However, according to the mounting structure of the conventional electronic device, the thermal stress caused by heat or the like generated when an electronic component such as a semiconductor element is operated causes the solder and the external connection pad to have a problem. When the voltage is repeatedly applied during this time, the nickel-tin alloy on the nickel plating layer of the external connection pad is apt to peel off, so that the electronic component cannot be normally operated for a long period of time. . The present invention has been completed in view of the above-mentioned problems, and an object of the present invention is to prevent the peeling between the nickel plating layer and the solder from occurring and keep the electronic component for a long period of time. It is an object of the present invention to provide a mounting structure of an electronic device that can be operated at a high speed. [0008] The electronic device mounting structure of the present invention is an electronic device comprising an electronic component mounted on an insulating base having external connection pads covered with a nickel layer on the lower surface. On an external electric circuit board having an electronic device connection pad on the upper surface, a mounting structure of an electronic device which is mounted by bonding the external connection pad and the electronic device connection pad via solder containing tin, An alloy layer containing copper, nickel and tin is formed on the nickel layer. According to the electronic device mounting structure of the present invention, since a substantially homogeneous alloy layer containing copper, nickel and tin is formed on the nickel plating layer covering the external connection pads of the electronic device, The nickel plating layer on the external connection pad and the solder are firmly joined via an alloy layer containing copper, nickel and tin. Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an example of an embodiment in which the present invention is applied to an electronic device on which a semiconductor element is mounted, wherein 1 is an electronic device, and 2 is an external electric circuit board. By mounting the electronic device 1 on the external electric circuit board 2 via the solder 3, the mounting structure of the electronic device of the present invention is formed. The electronic device 1 mainly includes an insulating base 4, an electronic component 5 mounted thereon, and a sealing member 6. In this example, the electronic component 5 is a semiconductor element such as an LSI, for example. The sealing member 6 is a sealing resin such as an epoxy resin. The insulating base 4 is made of a glass fabric in which glass fibers are woven vertically and horizontally and impregnated with a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin. A plurality of insulating layers 8 each made of a thermosetting resin such as a bismaleimide triazine resin are laminated, and a plurality of wiring conductors 9 made of copper foil or the like are formed from the upper surface to the lower surface. The core 7 constituting the insulating base 4 has a thickness of 0.1 mm.
It has a plurality of through holes 10 of about 3 to 1.5 mm and a diameter of about 0.2 to 1.0 mm from the upper surface to the lower surface. A part of the wiring conductor 9 is attached to the upper and lower surfaces and the inner wall of each through hole 10, and the wiring conductors 9 on the upper and lower surfaces are electrically connected through the through hole 10. The core 7 is formed by thermally curing a sheet in which a glass fabric is impregnated with an uncured thermosetting resin.
It is manufactured by performing drilling from the upper surface to the lower surface. The wiring conductors 9 on the upper and lower surfaces of the core 7 are attached with copper foil having a thickness of about 5 to 50 μm on the entire upper and lower surfaces of the sheet for the core 7 and are etched after the copper foil is cured. Thus, a predetermined pattern is formed. The wiring conductor 9 on the inner wall of the through-hole 10 is formed by depositing a copper foil having a thickness of about 5 to 50 μm on the inner wall of the through-hole 10 by providing the through-hole 10 on the core body 7 by electroless plating and electrolytic plating. Formed. Further, the core 7 is filled with a resin column 11 made of a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin inside the through hole 10. Resin pillar 11
Is intended to enable the insulating layer 8 to be formed directly above and directly below the through-hole 10 by closing the through-hole 10. An uncured paste-like thermosetting resin is screen-printed in the through-hole 10. And hardened by heat, and then the upper and lower surfaces are polished to be substantially flat. An insulating layer 8 is laminated on the upper and lower surfaces of the core 7 including the resin pillar 11. The insulating layers 8 laminated on the upper and lower surfaces of the core 7
A plurality of through holes 1 each having a thickness of about 20 to 50 μm and a diameter of about 30 to 100 μm from the upper surface to the lower surface of each layer.
Has two. These insulating layers 8 are provided to provide an insulating interval for wiring the wiring conductors 9 at high density, and the insulating layers 8 except for the outermost layer have surfaces and through holes.
A part of the wiring conductor 9 is attached in the inside 12. By electrically connecting the upper-layer wiring conductor 9 and the lower-layer wiring conductor 9 through the through-hole 12, high-density wiring can be formed three-dimensionally. Note that the outermost insulating layer 8 is a solder resist layer. Such an insulating layer 8 has a thickness of 20
A film of an uncured thermosetting resin having a thickness of about 50 μm is attached to the upper and lower surfaces of the core 7, which is thermally cured, and a through hole 12 is formed by laser processing. It is formed by sequentially stacking the insulating layers 8. The wiring conductor 9 attached to the surface of each insulating layer 8 and the inside of the through hole 12 has a thickness of about 5 to 50 μm on the surface of each insulating layer 8 and inside the through hole 12 every time the insulating layer 8 is formed. It is formed by applying a copper plating layer to a predetermined pattern by a known pattern forming method such as a semi-additive method or a subtractive method. The wiring conductor 9 formed from the upper surface to the lower surface of the insulating base 4 functions as a conductive path for connecting each electrode of the electronic component 5 to the external electric circuit board 2, and is exposed on the upper surface of the insulating base 4. The electronic component connection pad 14 is connected to the respective electrodes of the electronic component 5 via the solder 13 at the portion where the electronic component 5 is connected, and the portion exposed at the lower surface of the insulating base 4 is connected to the external electric circuit board 2 via the solder 3. External connection pads 15 are formed. In this example, each electrode of the electronic component 5 is connected to the electronic component connection pad 14 via the solder 13, but the electrode of the electronic component 5 is connected to the electronic component connection pad 14 via, for example, a bonding wire. Is also good. In that case, the electronic component connection pads 14 are arranged around the portion where the electronic component 5 is mounted. After connecting the electrodes of the electronic component 5 to the electronic component connection pads 14 on the upper surface of the insulating base 4 via the solder 13, the electronic component 5 is sealed with a sealing member 6 made of epoxy resin or the like. The electronic device 1 is completed, and the electronic device 1 is mounted on the external electric circuit board 2 by connecting the external connection pad 15 of the electronic device 1 to the electronic device connection pad 16 of the external electric circuit board 2 via the solder 3. Is done. In such an electronic device 1,
In order to facilitate the mounting on the external electric circuit board 2 via the solder 3, the solder 3 is previously attached to the external connection pad 15. By doing so, when the electronic device 1 is mounted on the external electric circuit board 2, it is possible to easily and surely hold and position the solder 3. At this time,
As the solder 3, for example, a solder containing about 0.25% by mass of copper in a lead-tin eutectic alloy is used. In order to attach the solder 3 to the external connection pad 15 in advance, first, as shown in an enlarged sectional view of a main part in FIG. A plating layer 17 and a gold plating layer 18 having a thickness of 0.01 to 0.8 μm are deposited, and a diameter of about 0.25% by mass of copper contained in, for example, a lead-tin eutectic alloy is added.
A spherical solder 3 of about 4 to 0.7 mm is brought into contact. Next, these are heated to a temperature higher than the melting temperature of the solder 3 in, for example, a nitrogen gas atmosphere and reflowed, and as shown in an enlarged sectional view of a main part in FIG. After being melted and solidified, the solder 3 is attached to the external connection pads. At this time, the gold plating layer 18 on the nickel plating layer 17 is diffused and absorbed into the molten solder 3 and disappears. Further, on the nickel plating layer 17, an alloy layer 19 having a thickness of about 0.5 to 5 μm containing copper, nickel and tin reacts with nickel in the nickel plating layer 17 and tin and copper in the solder 3 reacting. It is formed. Then, the nickel plating layer is interposed through the alloy layer 19.
17 and the solder 3 are firmly joined. As the nickel plating layer 17, for example, electroless nickel plating containing about 4 to 12% by weight of phosphorus is preferably used. As a plating solution for such a nickel plating layer 17, for example, nickel sulfate 40
g / l, sodium citrate 24 g / l, sodium acetate
Electroless nickel plating of 14 g / l, sodium hypophosphite 20 g / l, and ammonium chloride 5 g / l at a temperature of 50 to 90 ° C. is used. Examples of the plating solution for the gold plating layer 18 include an electroless gold plating solution having a temperature of 50 to 90 ° C. and including 5 g / l of potassium gold cyanide, 50 g / l of potassium citrate, and 5 g / l of sodium ethylenediaminetetraacetate. used. The nickel plating layer 17 is provided for preventing the external connection pads 15 from being oxidized and corroded, thereby making the connection between the external connection pads 15 and the solder 3 easy and strong. Is less than 0.5 μm, external connection pad 1
5 cannot be covered well and the external connection pad 15
Is liable to be oxidized or discolored on the surface, and the bonding with the solder 3 tends to be weak. On the other hand, if the thickness exceeds 10 μm, cracks and peeling are likely to occur in the nickel plating layer 17 due to the internal stress of the nickel plating layer 17. Become. Therefore, the thickness of the nickel plating layer 17 is preferably in the range of 0.5 to 10 μm. When the nickel plating layer 17 is made of electroless nickel plating containing phosphorus, if the content of phosphorus in the nickel plating layer 17 is less than 4% by weight, the nickel plating layer 17 When depositing, the deposition rate of nickel plating is slow, and it takes a long time to obtain a nickel plating layer 17 of a predetermined thickness, so that the productivity of the semiconductor device is extremely low. On the other hand, if it exceeds 12% by weight,
It becomes difficult to satisfactorily apply the gold plating layer 18 on the nickel plating layer 17. Therefore, the content of phosphorus in the nickel plating layer 17 is preferably in the range of 4 to 12% by weight. Further, the gold plating layer 18 to be adhered on the nickel plating layer 17 is for satisfactorily joining the nickel plating layer 17 and the solder 3 and has a thickness of 0.01 μm.
If it is less than m, the bonding between the nickel plating layer 17 and the solder 3 tends to be weak. On the other hand, if it exceeds 0.8 μm, a large amount of gold melts into the solder 3 and the solder 3 becomes brittle. Separation is likely to occur between the nickel plating layer 17 and the solder 3 due to stress due to heat or the like generated when the electronic component 5 operates. Therefore, the thickness of the gold plating layer 18 is 0.01 to
A range of 0.8 μm is preferred. The nickel plating layer 17 and the gold plating layer 18 may be applied, for example, before connecting the electrodes of the electronic component 5 to the electronic component connection pads 14 of the insulating base 1. At the same time, a nickel plating layer and a gold plating layer may be similarly applied to the electronic component connection pads. By doing so, it is possible to effectively prevent the electronic component connection pad 14 from being oxidized and corroded, and it is possible to easily and firmly join the electronic component connection pad 14 and the solder 13. On the other hand, the external electric circuit board 2 on which the electronic device 1 is mounted is, for example, a general printed circuit board, and a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin is added to a glass fabric in which glass fibers are woven vertically and horizontally. A plurality of electronic device connection pads are provided on the upper surface of the insulating plate 20 impregnated with resin.
16 is formed. The electronic device connection pad 16 may be formed by depositing a nickel plating layer on a copper foil or may be formed only of a copper foil. Such an external electric circuit board 2 is manufactured by an ordinary method. Then, the electronic device 1 is connected to the external electric circuit board 2.
In order to mount the electronic device 1, the electronic device 1 is placed on the external electric circuit board 2 so that the solder 3 previously attached to the external connection pad 15 and the electronic device connection pad 16 are in contact with each other. A method is employed in which the solder 3 is melted by heating to a temperature higher than the temperature at which the solder 3 melts in a gas atmosphere. At this time, as shown in an enlarged sectional view of a main part in FIG. 3, the nickel plating layer of the external connection pad 15 of the electronic device 1 is formed.
Since an alloy layer 19 containing copper, nickel and tin is previously formed on 17, an electronic device connection pad 16 of the external electric circuit board 2 is formed by depositing a nickel plating layer on a copper foil. Even in the case where it is made of only copper foil, a substantially uniform alloy layer 19 containing copper, nickel and tin and having a thickness of about 0.05 to 10 μm is formed on the nickel plating layer 17. Since the alloy layer 19 containing copper, nickel and tin is formed on the nickel plating 17 on the external connection pad 15 in this manner, the nickel plating layer 17 on the external connection pad 15 and the solder 3 Are firmly joined via an alloy layer 19 containing copper, nickel and tin, and as a result, even if thermal stress due to heat or the like generated during operation of the electronic component 5 is repeatedly applied, the external connection pads 15 The electronic component 5 can be operated normally and stably for a long period of time without peeling between the solder and the solder 3. The thickness of the alloy layer 19 containing copper, nickel and tin formed on the nickel plating layer 17 is 0.05 μm.
If it is less than m, the adhesion between the nickel plating layer 17 and the alloy layer 19 is poor, and peeling may occur between them.
If it exceeds μm, an alloy layer containing copper, nickel and tin 19
Breakage may occur from inside. Therefore, the thickness of the alloy layer 19 containing copper, nickel and tin formed between the nickel plating layer 17 and the solder 3 is preferably in the range of 0.05 to 10 μm. EXAMPLE As a substrate for evaluation, two insulating layers made of epoxy resin and having a thickness of 35 μm were laminated on a 1.6 mm thick core obtained by impregnating a glass fabric with an epoxy resin. A solder resist with a thickness of 25 μm from copper plating made of acrylic-modified epoxy resin is formed on each of ten approximately circular test pads with a diameter of 0.6 mm consisting of a copper plating layer with a thickness of 15 μm on the insulating layer. The layer was applied so as to have an opening having a diameter of 0.5 mm concentric with the test pad, and a nickel plating layer having a thickness of 3 μm and a thickness of 0.06 μm were formed on the surface of the test pad exposed from the opening of the solder resist layer. with providing a evaluation substrate with a gold plating layer are sequentially deposited, the on the test pad, a lead - tin eutectic peak solder volume which contains 0.25% by weight of copper alloy 0.1 mm ³ After forming a solder bump by melting at a soldering temperature of 230 ° C, this is applied to a nickel plating layer on copper foil. The connection pad with a thickness of 15 μm and a diameter of 0.53 mm corresponds to the test pad on the evaluation board. The solder bumps formed on the evaluation board are melted at a peak temperature of 230 ° C, and the connection pads on the printed board and the test pads on the evaluation board are joined via the solder bumps. Thus, a first evaluation sample according to the present invention was obtained. Further, on a test pad of the above-described evaluation substrate, a solder having a volume of 0.1 mm ³ containing 0.25% by mass of copper in a lead-tin eutectic alloy was melted at a peak temperature of 230 ° C. to form a solder bump. After that, this was changed to 12
A connection pad having a diameter of 0.53 mm and a diameter of 0.53 mm is placed on a printed circuit board having a position corresponding to the test pad on the evaluation board, and the solder bumps formed on the evaluation board are melted at a peak temperature of 230 ° C. The connection pads and the test pads of the evaluation substrate were joined via solder bumps to obtain a second evaluation sample according to the present invention. The first and second evaluation materials according to the present invention include 18 to 30% by mass of copper, 0.3 to 5% by mass of nickel and 50 to 60% by mass between the nickel plating layer and the solder bump on the test pad. % Of tin was formed to a thickness of 0.05 to 10 μm. Further, a solder made of a lead-tin eutectic alloy and having a volume of 0.1 mm ³ was melted at a peak temperature of 220 ° C. on a pad of the above-mentioned evaluation substrate to form a solder bump, and this was formed only from copper foil. A connection pad having a thickness of 12 μm and a diameter of 0.53 mm is placed on a printed circuit board having a position corresponding to the test pad on the evaluation board, and the solder bumps formed on the evaluation board are melted at a peak temperature of 220 ° C. The connection pads on the printed board and the test pads on the evaluation board were joined via solder bumps to obtain evaluation samples for comparison. In the evaluation sample for comparison, a nickel-tin alloy layer having a thickness of 0.05 to 20 μm and an alloy layer containing copper, nickel and tin were formed between the nickel plating layer and the solder bump on the test pad. . The thus-obtained evaluation substrate of each evaluation sample was peeled off the printed circuit board, and the peeled surface was observed. As a result, in the evaluation sample according to the present invention,
In all the test pads, peeling occurred between the test pad and the insulating layer, and it was confirmed that the nickel plating layer and the solder were extremely strongly bonded. On the other hand, in the evaluation samples for comparison, peeling occurred between the nickel plating layer and the solder in all the test pads, and it was confirmed that the bonding strength between the nickel plating layer and the solder was weak. Thus, according to the electronic device mounting structure of the present invention, the electronic component 5 can be normally operated for a long period of time. It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention. In one example, the insulating base 4 is formed of a material obtained by impregnating a glass fabric with a thermosetting resin and a thermosetting resin. However, the insulating base 4 may be formed of another insulating material such as a ceramic material. Well, the wiring conductor 8
Other conductive materials such as metallized conductors of metal powder such as tungsten or molybdenum / copper / silver can be used. Further, in the example of the above-described embodiment, the alloy layer 19 containing copper, nickel, and tin is formed on the nickel plating layer 17 by including copper in the solder 3. A copper-containing plating layer is deposited on the surface, and copper, nickel and tin are contained on the nickel plating layer 17 by melting the solder 3 made of a lead-tin eutectic alloy containing no copper. Alloy layer 19
May be formed. According to the electronic device mounting structure of the present invention,
Since the alloy layer containing copper, nickel, and tin is formed on the nickel plating layer of the external connection pad of the electronic device, the nickel plating of the external connection pad is performed by the alloy layer containing copper, nickel, and tin. As a result, the external connection pads and the solder are not separated from each other even if thermal stress due to heat or the like generated during operation of the electronic component is repeatedly applied. For normal operation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example of an embodiment of a mounting structure of an electronic device of the present invention. FIGS. 2A and 2B are enlarged cross-sectional views of a main part for describing a method of attaching solder 3 to an external connection pad 15 of the electronic device 1 shown in FIG. 1 in advance. FIG. 3 is an enlarged sectional view of a main part of the mounting structure of the electronic device shown in FIG. 1; [Description of Signs] 1 ... Electronic device 2 ... External electric circuit board 3 ... Solder 4 ... Insulating base 5 ... Electronic component 15 ... ..Pad 17 for external connection Nickel plating layer 16 Pad 19 for electronic device connection Alloy layer containing copper, nickel and tin

Claims (1)

Claims: 1. An electronic device comprising an electronic component mounted on an insulating base having external connection pads covered with a nickel layer on a lower surface, and an external electric circuit having electronic device connection pads on an upper surface. A mounting structure of an electronic device, which is mounted on a substrate by bonding the external connection pad and the electronic device connection pad via solder containing tin, wherein copper and nickel are provided on the nickel layer. An electronic device mounting structure, wherein an alloy layer containing tin is formed.