JP2006270008A - Lead-free soldering board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free soldering board and its manufacturing method wherein, when a lead of an electronic component is soldered by use of a lead-free solder, voids, etc. are not formed in lead-free soldering in a through hole of the board. <P>SOLUTION: In this board, a lead 8a of an electronic component 8 is inserted into a through-hole 17 of the board, and lead-free solder 16 is filled in the through-hole by flow treatment to solder the lead of the electronic component. This board is a metal core board 10 in which both faces of a metal layer 11 are covered with a resin layer 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lead-free soldering substrate and a method for manufacturing the same, and the substrate is used in, for example, an electric connection box mounted on a vehicle or the like.

  Conventionally, a glass epoxy substrate has been generally used as a substrate, and flow soldering is performed in order to perform soldering in the through hole. In recent years, so-called lead-free solder that does not contain lead has been used as an environmental measure (for example, Patent Document 1).

JP 2000-35164 A

  However, for example, as shown in FIG. 3, a printed circuit board 1 provided with a glass epoxy substrate 2 having an electrode 3 and a through hole 7 penetrating in the thickness direction of the glass epoxy substrate 2 and a plating layer 4 for plating the electrode 3 and the through hole 7. Furthermore, when the lead 8 a of the electronic component 8 is inserted into the through hole 7 and soldered with the lead-free solder 6, the phenomenon that the lead-free solder 6 may spread and the wettability may deteriorate in the through hole 7 occurs. It was. For this reason, voids are generated in the lead-free solder 6 filled in the through holes 7, or voids are formed in the interface between the lead 8a and the lead-free solder 6, the interface between the plating layer 4 and the lead-free solder 6, or the like. As a result, there is a risk that sufficient bonding strength between the electronic component 8 and the printed circuit board 1 cannot be obtained, or that there is a problem in terms of thermal shock resistance.

In view of the above situation, the inventor conducted the following intensive studies.
First of all, lead-free solder generally has a melting point higher than about 180 ° C., which is the melting point of eutectic solder, and above 200 ° C. Therefore, at about 240 ° C., it is considered that lead-free solder is poorly melted, causing problems of viscosity and wettability, resulting in poor solder formation such as voids.

  Secondly, although the solder should be melted at a lead-free solder temperature of 240 ° C., the solder adhesion may worsen, rather, the temperature of the glass-epoxy substrate is unlikely to rise rapidly to 240 ° C. This is probably because the temperature of the lead-free solder is lowered to a temperature lower than or equal to the melting point when the lead-free solder comes into contact with a low temperature substrate. In order to improve this, it is conceivable to increase the temperature of the lead-free solder to 260 ° C. or higher, but there is a problem in terms of heat resistance of the substrate such as an electronic component or a resin layer on the substrate. It was also found that when post-flux was used to improve the adhesion of lead-free solder, gas was generated from the post-flux at 260 ° C. or higher, resulting in bubbles and more voids. . As another method, when the flow process is performed slowly so that the temperature of the glass epoxy substrate follows 240 ° C., which is the same as the solder temperature, the process takes too much time and the productivity of the soldered substrate is deteriorated.

  The present invention has been made on the basis of the above study, and lead-free solder that does not generate voids in the lead-free solder in the through hole of the board when the lead of the electronic component is soldered using lead-free solder. It is an object of the present invention to provide a soldering substrate and a manufacturing method thereof.

  In order to solve the above-described problem, the lead-free soldered board according to claim 1 is configured such that the lead of the electronic component is inserted into the through hole of the board, and the lead-free solder is filled into the through hole by a flow process. A lead-free soldering board to which leads of the electrical component are soldered, wherein the board is a metal core board in which both surfaces of a metal layer are covered with a resin layer.

  A lead-free soldering board according to claim 2 is characterized in that, in the invention according to claim 1, the thickness of the metal layer is 0.3 to 0.6 mm.

  The lead-free soldering board according to claim 3 is the invention according to claim 1 or 2, wherein the resin layer is formed by bonding the metal layer to a plurality of resin sheets, and the resin sheet. The thickness is 0.2 to 0.4 mm.

  The lead-free soldering board according to claim 4 is the invention according to any one of claims 1 to 3, wherein the total thickness of the metal layer and the resin layer is 0.9 to 1.2 mm. It is characterized by being.

  According to a fifth aspect of the present invention, there is provided a method for manufacturing a lead-free soldered substrate, wherein the lead of the electronic component is inserted into the through hole of the substrate, and the lead-free solder is filled into the through hole by a flow process. In the method of manufacturing a lead-free soldered substrate for soldering leads, the substrate is a metal core substrate.

  According to a sixth aspect of the present invention, there is provided the method for producing a lead-free soldered substrate according to the fourth aspect of the invention, wherein the solder has a melting point of 230 ° C. or less, and the lead-free solder temperature in the flow treatment is 220 to It is 255 degreeC.

  According to a seventh aspect of the present invention, there is provided a method for manufacturing a lead-free soldered substrate according to the fifth aspect, wherein the metal layer is exposed from a part of an end surface of the metal core substrate, and the lead-free solder in the flow process is used. Soldering is performed from the end face side where the metal layer is exposed.

  The lead-free soldering board manufacturing method according to claim 8 is the method according to claim 6, wherein the metal layer is exposed before the solder jet for performing lead-free soldering reaches the first soldering portion. The solder jet is brought into contact with the end of the solder for 0.1 second or longer.

  In the lead-free soldering board according to claim 1 of the present invention, the lead of the electronic component is inserted into the through hole of the substrate, the lead-free solder is filled into the through hole by flow processing, and the lead of the electric component is soldered Since the metal core board with both sides of the metal layer covered with a resin layer is used as the printed board, the heat generated by the solder jet flow is rapidly equalized to a temperature close to or close to the solder jet flow by the metal layer of the metal core board. In addition, it is not necessary to raise the temperature of the lead-free solder to a temperature higher than necessary, and it is possible to obtain a good connection state between the electronic component and the substrate that does not generate voids.

  In addition, when the thickness of the metal layer of the lead-free soldering substrate is 0.3 to 0.6 mm, it is possible to prevent the occurrence of barrel cracks in the plating layer formed in the through hole, and to equalize. It is also preferable in terms of heat speed and substrate strength.

  Further, when the resin sheet forming the resin layer of the lead-free soldering substrate has a thickness of 0.2 to 0.4 mm, occurrence of barrel cracks in the plating layer formed in the through hole is prevented. In addition, it is preferable in terms of heat conduction to the metal layer, substrate strength, and insulation.

  Further, when the total thickness of the metal layer and the resin layer of the lead-free soldering substrate is 0.9 to 1.2 mm, occurrence of barrel cracks in the plating layer formed in the through hole is prevented. This is preferable.

  According to a fifth aspect of the present invention, there is provided a method of manufacturing a lead-free soldered substrate, wherein the lead of the electronic component is inserted into the through hole of the substrate, and the lead-free solder is filled into the through hole by a flow process. In the method of manufacturing a lead-free soldering board for soldering the leads of the lead, the board is a metal core board, so that the heat from the solder jet is rapidly equalized to a temperature close to or close to the solder jet by the metal layer of the metal core board. It is possible to obtain a good connection state between the electronic component and the substrate that is heated and does not need to raise the temperature of the lead-free solder to a temperature higher than necessary and does not generate voids.

  Further, in the method for producing a lead-free soldered substrate, when the melting point of the solder is 230 ° C. or less and the temperature of the lead-free solder in the flow process is 220 to 255 ° C., the connection state between the electronic component and the substrate This is preferable from the viewpoint of preventing thermal deterioration of electronic components and substrates.

  In the lead-free soldering board manufacturing method, a metal layer is exposed from a part of the end face of the metal core board, and the lead-free soldering in the flow process is performed from the end face side where the metal layer is exposed. It is preferable in terms of heat conduction to the metal layer. Further, before the solder jet for performing lead-free soldering reaches the first soldering portion, the solder jet is applied to the end portion where the metal layer is exposed. Is more preferable for 0.1 seconds or more.

  In the embodiment of the present invention, the structure of a lead-free soldering substrate will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view of a lead-free soldering board showing an embodiment of a lead-free soldering board according to the present invention.

  As shown in FIG. 1, the lead-free soldering substrate 20 according to the present embodiment includes a metal core substrate 10 in which both surfaces of a metal layer 11 made of a metal such as copper or aluminum are covered with a resin layer 12 such as glass epoxy, A resist layer used in a circuit forming process such as an electrode 13 and a through hole 17 penetrating the metal core substrate 10 in the thickness direction of the metal core substrate 10, a plating layer 14 for plating the inner wall of the electrode 13 and the through hole 17, and the electrode 13. 15, the lead 8 a of the electronic component 8 is inserted into the through hole 17 and soldered with lead-free solder 16.

  Although the metal core substrate 10 is not shown in a plan view, the metal core substrate 10 is square or round when viewed from above, and the metal layer 11 is exposed at the end. That is, when the metal core substrate 10 is a quadrangle when viewed from the top, the metal layer 11 is exposed when the four sides are viewed from the side. The thickness of the metal layer 11 is preferably in the range of 0.3 mm to 0.6 mm. The reason for this is that if the thickness of the metal layer 11 is less than 0.3 mm, the strength of the substrate is impaired, and the entire metal core substrate 10 is maintained at a uniform temperature in the flow soldering process, so that the thickness is 0.3 mm or more. When the thickness of the metal layer 11 exceeds 0.6 mm, barrel cracks are generated in the plated layer formed in the through hole as shown in Table 1 of Examples described later. In addition, the speed at which the entire metal core substrate 10 is soaked in the flow soldering process is reduced, and there is a possibility that the soldering is performed before the temperature of the metal core substrate 10 is sufficiently increased. Therefore, the thickness of the metal layer 11 is preferably in the range of 0.3 mm to 0.6 mm. In the present embodiment, the thickness of the metal layer 11 is set to 0.4 mm. The material of the metal layer is preferably copper from the viewpoint of thermal conductivity.

  Moreover, it is preferable that the thickness of the resin sheet (resin layer 12) bonded to both surfaces of the metal layer 11 is in a range of 0.2 mm to 0.4 mm. This is because, in the process of manufacturing the metal core substrate 10 to be described later, the hole to be formed in the metal layer 11 is temporarily filled with a resin sheet (after that, the hole is formed again), but the thickness of the resin sheet is 0. If it is less than 2 mm, the amount of resin is insufficient, and the through-hole formation planned portion cannot be filled with resin, and the insulation distance between the metal layer 11 and the electrode 13 cannot be secured in the completed metal core substrate 10. On the other hand, if the thickness exceeds 0.4 mm, heat transfer to the metal core substrate 10 is performed through the resin layer 12 in the flow soldering process, so that the rate of soaking is reduced and as shown in Table 2 of Examples described later. In addition, barrel cracks occur in the plating layer formed in the through hole. In this embodiment, the thickness of the resin sheet is set to 0.2 mm, and the resin sheet is bonded to both surfaces of the metal layer 11 of the resin sheet one by one. Therefore, the total thickness of the metal core substrate 10 is 0.2 + 0.4 + 0.2 = 0.8 (mm).

  In addition, the alloy used for the lead-free solder 16 is variously used, such as an alloy in which Bi, In, Cu or the like is added to Sn—Ag, Sn—Bi, Sn—Zn, Sn—In, or the like. However, in the present invention, it is desirable that the alloy is a Sn—Ag—Cu alloy and the solder has a melting point of 230 ° C. or less. This is because if the melting point of the solder exceeds 230 ° C., the temperature of the solder jet exceeds 255 ° C., and the electronic component 8 and the resin layer 12 mounted on the metal core substrate 10 may be thermally deteriorated. It is. In the present embodiment, an alloy composed of Ag 3.5 wt%, Cu 0.5 wt%, the balance Sn and inevitable impurities and having a melting point of 220 ° C. is used.

Next, a method for manufacturing a lead-free soldered substrate will be described.
First, a hole for forming a through hole is formed in the plate-like metal layer 11 with a drill or the like. As shown in FIG. 2, the diameter of the hole is a total value of the hole diameter d of the through hole 17, the thickness f (× 2) of the plating layer 14, and the thickness e (× 2) of the resin layer in the through hole 17. It becomes. Next, one sheet-like prepreg (resin sheet) made of glass epoxy or the like is disposed on both surfaces of the metal layer 11, and the resin sheets are bonded and cured by pressing and heating. Next, the through hole is formed again with a drill or the like. The diameter of the hole at this time is a total value of the hole diameter d of the through hole and the thickness f (× 2) of the plating layer as shown in FIG. Next, a circuit is formed by printing and covering the electrode 13 with a resist layer 15 to form a plated layer 14 of a metal such as copper on the electrode 13 and the inner surface of the hole, and through holes 17 are formed. To obtain the metal core substrate 10.
Finally, the lead 8a of the electronic component 8 is inserted into the through hole 17 and subjected to flow treatment with the lead-free solder 16 and soldered.

  In the flow process, it is desirable that the melting point of the lead-free solder 16 is 230 ° C. or less, and the temperature of the lead-free solder 16 in the flow process is 220 to 255 ° C. This is because if the temperature of the lead-free solder 16 in the flow process is less than 220 ° C., the connection strength between the electronic component and the substrate may be insufficient, and if it exceeds 255 ° C., the electronic component 8 mounted on the metal core substrate 10 may be insufficient. This is because the resin layer 12 may be thermally deteriorated.

  Further, when the flow process is performed from the end face side of the metal core substrate 10, the heat of the solder jet flow is easily transmitted to the metal layer 11 exposed from the end face of the metal core substrate 10, so that the entire metal core substrate is easily heated and the inside of the through hole 17. Thus, the generation of voids in the lead-free solder 16 can be prevented. Note that this effect becomes more prominent if the solder jet is brought into contact with the end where the metal layer is exposed for 0.1 second or more before the solder jet reaches the first soldering portion. In this embodiment, the contact is made for 0.5 seconds.

  In addition, it is desirable that the processing speed of the flow processing is as slow as possible from the viewpoint of soaking the metal core substrate 10, and it is preferably about 2 m / min or less. However, if the processing speed is too slow, productivity may be hindered. In the form, it is set at 0.6 m / min. Note that the contact width between the solder jet and the metal core substrate 10 is preferably as wide as possible from the viewpoint of heat equalization of the metal core substrate 10 and is preferably 10 mm or more. In this embodiment, the contact width is set to 70 mm.

  Further, if the metal core substrate 10 is pre-heated before the flow treatment, the soaking of the metal core substrate 10 becomes more efficient, and the effect of the present invention becomes more remarkable.

[Example 1]
As shown in FIG. 2, the thickness of the metal layer 11 is a (mm), the thickness of the resin sheet is b (mm), and the total of the metal layer 11 and the resin layer 12 after the resin sheet is bonded to the metal layer 11. The thickness is c (mm), the hole diameter of the through hole 17 is d (mm), the distance between the metal layer 11 and the plating layer 14 in the through hole 17 is e (mm), and the thickness of the plating layer 14 is f (mm). ), Various changes were made to the thickness a (mm) of the metal layer 11 to confirm the presence or absence of barrel cracks in the plating layer 14, the strength of the metal core substrate 10, and the influence on the flow soldering process, which is a subsequent process. An experiment was conducted. The results are shown in Table 1. The thickness b of the resin sheet is set to 0.2 mm, the hole diameter d of the through hole 17 is set to 1.0 mm, the distance e is set to 0.5 mm, and the thickness f of the plating layer 14 is set to 0.5 mm. Moreover, it is preferable to use a resin sheet having a linear expansion coefficient of 40 to 60 (10 ⁻⁶ / ° C.). In Example 1, a resin sheet having a linear expansion coefficient of 40 (10 ⁻⁶ / ° C.) is used. did.

  As shown in Table 1, when the thickness a of the metal layer 11 is in the range of 0.3 to 0.6 mm, barrel cracks do not occur in the plating layer 14, and the strength of the metal core substrate 10 and the flow soldering process are also good. It turns out that it is a state. Further, when the thickness a of the metal layer 11 exceeds 0.6 mm, barrel cracks occur in the plating layer 14, and when the thickness a of the metal layer 11 is less than 0.3 mm, barrel cracks and the like do not occur, It has been found that the strength and soaking capability of the metal core substrate 10 are impaired, which affects the subsequent mounting of the electronic component 8 on the metal core substrate 10 and the flow soldering process.

[Example 2]
In Example 2, the thickness b of the resin sheet was changed variously under the same conditions as in Example 1 to determine whether or not barrel cracks occurred in the plating layer 14, the strength of the metal core substrate 10, and the flow solder process, which is a subsequent process. Experiments were conducted to confirm the effects of The results are shown in Table 2. The thickness a of the metal layer 11 was set to 0.4 mm.

As shown in Table 2, when the thickness b of the resin sheet is in the range of 0.2 to 0.4 mm, barrel cracks or the like do not occur in the plating layer 14, and the strength of the metal core substrate 10 and the flow soldering process are also good. It turns out that it is a state. Further, if the thickness b of the resin sheet exceeds 0.4 mm, barrel cracks occur in the plating layer 14 and heat transfer from the metal core substrate 10 through the solder jet flow through the resin layer 12 in the flow soldering process. It has been found that if the resin layer 12 is too thick, that is, if the thickness of the resin sheet exceeds 0.4 mm, the heat supply to the metal layer 11 is impaired, and the soaking rate of the entire metal core substrate 10 is reduced. In addition, when the thickness b of the resin sheet is less than 0.2 mm, barrel cracks and the like are not generated. However, as described above, the resin sheet is filled when filling the through-hole formation planned portion that occurs in the manufacturing stage of the metal core substrate 10. The through-hole formation planned portion cannot be filled with resin because the amount of resin supplied from the metal is insufficient, and the insulation distance between the metal layer 11 and the electrode 13 cannot be secured in the completed metal core substrate 10. It became clear that there were problems such as insufficient strength.
From the results of Example 1 and Example 2, the total thickness of the metal layer 11 and the resin layer 12 is preferably in the range of 0.8 to 1.2 mm.

Example 3
In Example 3, under the same conditions as in Example 1, various changes were made to the hole diameter d of the through hole 17 to determine whether or not barrel cracks occurred in the plated layer 14, the strength of the metal core substrate 10, and the flow solder process, which is a subsequent process. Experiments were conducted to confirm the effects of The results are shown in Table 3. In addition, the thickness a of the metal layer 11 was set to 0.4 mm, and the thickness b of the resin sheet was set to 0.2 mm.

  As shown in Table 3, it was found that barrel cracks occurred in the plated layer 14 when the through hole 17 had a hole diameter d of 0.9 mm or less. Accordingly, it is desirable that the through hole 17 has a hole diameter of 1.0 or more.

It is sectional drawing of the board | substrate which concerns on embodiment of this invention. It is explanatory drawing of the board | substrate which concerns on the Example of this invention. It is sectional drawing of the conventional board | substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Glass epoxy board 3 Electrode 4 Plating layer 6 Lead free solder 7 Through hole 8 Electronic component 8a Lead 10 Metal core board 11 Metal layer 12 Resin layer 13 Electrode 14 Plating layer 15 Resist layer 16 Lead free solder 17 Through hole 20 Lead free Soldering board

Claims (8)

  A lead-free soldering board in which a lead of an electronic component is inserted into a through-hole of the board, lead-free solder is filled in the through-hole by a flow process, and the lead of the electrical component is soldered. A lead-free soldering board characterized by being a metal core board in which both surfaces of a metal layer are covered with a resin layer.   The lead-free soldering board according to claim 1, wherein the metal layer has a thickness of 0.3 to 0.6 mm.   3. The resin layer according to claim 1, wherein the resin layer is formed by laminating a plurality of resin sheets to the metal layer, and the thickness of the resin sheet is 0.2 to 0.4 mm. Lead-free soldering board.   The lead-free soldering substrate according to any one of claims 1 to 3, wherein a total thickness of the metal layer and the resin layer is 0.9 to 1.2 mm.   In the method of manufacturing a lead-free soldered substrate, the lead of the electronic component is inserted into the through-hole of the substrate, and the lead-free solder is filled into the through-hole by flow processing to solder the lead of the electrical component. A method for producing a lead-free soldering board, characterized in that is a metal core board.   5. The method for producing a lead-free soldering board according to claim 4, wherein the solder has a melting point of 230 ° C. or lower, and the temperature of the lead-free solder in the flow treatment is 220 to 255 ° C. 6.   6. The metal layer is exposed from a part of an end surface of the metal core substrate, and the lead-free soldering in the flow process is performed from the end surface side where the metal layer is exposed. The manufacturing method of the lead-free soldering board of description.   7. The method of manufacturing a lead-free soldering board according to claim 6, wherein the solder jet is applied to an end portion where the metal layer is exposed before the solder jet for performing lead-free soldering reaches the first soldering portion. A method for producing a lead-free soldering substrate, wherein the contact is performed for 0.1 second or more.

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