JP2005158892A - Process for producing wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board capable of connecting the electrode of an electronic component normally with a connection pad through solder by recognizing a mark for positioning the electronic component accurately through an image recognition system. <P>SOLUTION: After first solder paste 21 is printed on a mark 3 for positioning an electronic component formed of a conductor layer on the surface of an insulating substrate 1, solder 6 in the first solder paste 21 is thermally fused and welded to the mark 3. Subsequently, second solder paste 23 having viscosity higher than that of the first solder paste 21 is printed on a connection pad 2a formed of the same conductor layer as that of the mark 3 on the surface of the insulating substrate 1 and then solder 4 in the second solder paste 23 is thermally fused and welded to the connection pad 2a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wiring board used for mounting electronic components such as semiconductor elements.

  Conventionally, wiring boards used for mounting electronic components such as semiconductor elements are the interior and surface of an insulating substrate formed by laminating a plurality of insulating layers made of an insulating plate made of, for example, a glass-epoxy plate or an epoxy resin. And a wiring conductor made of a conductor layer such as a copper foil or a copper plating film. In such a wiring board, a part of the conductor layer provided on the surface of the insulating substrate forms a plurality of connection pads that are electrically connected to electrodes of electronic components such as semiconductor elements via solder, A solder resist layer having an opening for exposing each connection pad is deposited on the surface of the insulating substrate on which these connection pads are formed. Furthermore, solder is previously deposited on the connection pad exposed from the solder resist layer, thereby facilitating connection between the connection pad and the electrode of the electronic component via the solder.

  In order to weld the solder to the connection pad in such a wiring board, the solder paste is printed on the exposed surface of the connection pad made of a conductor layer such as a copper foil or a copper plating film by a screen printing method, and then the solder paste The method of heating and melting and welding is adopted.

  In this wiring board, after positioning the electrode of the electronic component to the connection pad to which the electrode of the electronic component is connected, the electronic component is mounted by joining the electrode of the electronic component and the connection pad via solder. Become an electronic device.

By the way, in such a wiring board, in order to align the electrode of the electronic component with the connection pad, an automatic machine having an image recognition device is generally used, and the electronic component is positioned on the upper surface of the insulating substrate. An electronic component positioning mark serving as a reference for alignment is provided, and this mark is recognized by an automatic image recognition device, and the position is automatically aligned based on the information. The electronic component positioning mark is formed on the surface of the insulating substrate by the same conductor layer as the connection pad, and solder for preventing oxidation and discoloration of the mark is welded to the surface. The solder deposited on the surface of the mark has the same composition as the solder deposited on the connection pad. When printing the solder paste on the connection pad, the same solder paste is printed on the mark at the same time. It is welded by heating and melting the solder in the paste.
JP 10-2105060 A

  In recent years, lead-free solder containing no lead has been used as a solder for connecting electrodes of electronic components and connection pads of a wiring board in consideration of the environment. Such lead-free solder is inferior in wettability to the conductor layer forming the connection pad and the electronic component positioning mark, and is less likely to spread on the electronic component positioning mark than the conventional lead-tin solder. Therefore, in order to cover the entire surface of the mark, it is necessary to deposit a larger amount on the mark than before. However, when a large amount of solder is deposited on the electronic component positioning mark, a part of the melted solder collects due to surface tension and becomes a large convex shape, thereby disturbing the reflection of light on the mark. As a result, a problem that the mark recognition by the image recognition apparatus becomes difficult is induced. In addition, as shown in Patent Document 1, solder may not be welded to the mark, but in this case, the exposed mark is likely to be oxidized or discolored. There is a greater risk that oxidation or discoloration will occur, making it difficult to recognize the mark well.

  The present invention has been devised in view of such conventional problems, and an object of the present invention is to reduce the thickness of the mark surface evenly even if the amount of solder welded to the electronic component positioning mark is small. Provided is a wiring board that can be satisfactorily coated with solder, and can accurately recognize a mark with an image recognition device and normally connect an electrode of an electronic component and a connection pad via solder. There is.

  In the method for manufacturing a wiring board according to the present invention, the first solder paste is printed on the electronic component positioning mark formed by the conductor layer on the surface of the insulating substrate, and then the solder in the first solder paste is heated. A step of melting and welding solder to the mark; and a connection pad formed on the surface of the insulating substrate by the same conductor layer as the mark, to which an electrode of an electronic component is connected via solder. And a step of printing the second solder paste having a higher viscosity than the solder paste and then heating and melting the solder in the second solder paste to weld the solder to the connection pad. Is.

  According to the method for manufacturing a wiring board of the present invention, the first solder paste printed on the electronic component positioning mark has a lower amount of viscosity than the second solder paste printed on the connection pad. However, since it is thinly spread on the mark and printed, the solder in the paste is heated and melted, so that a thin uniform thickness of solder can be deposited on the mark and the second solder paste printed on the connection pad Since the viscosity is higher than that of the first solder paste, it is printed thickly without spreading thinly, so that a sufficiently high solder can be deposited on the connection pad. Therefore, a wiring board capable of accurately recognizing the mark with the solder welded by the image recognition apparatus and properly connecting the electrode of the electronic component and the connection pad through a sufficiently high solder. Can be provided.

  Next, a method for manufacturing a wiring board according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an example of an embodiment of a wiring board manufactured by the manufacturing method of the present invention. In FIG. 1, 1 is an insulating substrate, 2 is a wiring conductor, 2a and 2b are connection pads, 3 is a mark for positioning an electronic component, 4, 5 and 6 are solders, and 7 is a solder resist layer. A wiring board for mounting the semiconductor element 8 is configured.

  The insulating substrate 1 is made of, for example, epoxy resin or bismaleimide triazine on the upper and lower surfaces of a plate-like core 1a formed by impregnating a glass fabric in which glass fibers are woven vertically and horizontally with a thermosetting resin such as epoxy resin or bismaleimide triazine resin. A plurality of insulating layers 1b made of a thermosetting resin such as a resin are laminated, and a plurality of wiring conductors 2 made of a conductor layer such as a copper foil or a copper plating film are formed from the upper surface to the lower surface.

  The core 1a constituting the insulating substrate 1 has a thickness of about 0.3 to 1.5 mm and has a plurality of through holes 9 having a diameter of about 0.2 to 1.0 mm from the upper surface to the lower surface. . A part of the wiring conductor 2 is attached to the upper and lower surfaces and the inner surface of each through hole 9, and the upper and lower wiring conductors 2 are electrically connected via the inner surface of the through hole 9.

  Such a core 1a is manufactured by thermally curing a sheet in which a glass fabric is impregnated with an uncured thermosetting resin, and then drilling the sheet from the upper surface to the lower surface. The wiring conductor 2 on the upper and lower surfaces of the core body 1a has a copper foil having a thickness of about 5 to 50 μm adhered to the entire upper and lower surfaces of the sheet for the core body 1a, and this copper foil is etched after the sheet is cured. By doing so, a predetermined pattern is formed. Further, the wiring conductor 2 on the inner surface of the through hole 9 is provided with a copper plating film having a thickness of about 5 to 50 μm on the inner surface of the through hole 9 by electroless plating and electrolytic plating after the through hole 9 is provided in the core body 1a. Formed by precipitation.

  Further, the core body 1a is filled with a resin column 10 made of a thermosetting resin such as an epoxy resin or a bismaleimide triazine resin in the through hole 9 thereof. The resin pillar 10 is for making it possible to form the insulating layer 1b directly above and below the through-hole 9 by closing the through-hole 9, and an uncured paste-like thermosetting resin is put into the through-hole 9. After filling with a screen printing method and thermosetting it, the upper and lower surfaces thereof are polished to be substantially flat. And the insulating layer 1b is laminated | stacked on the upper and lower surfaces of the core 1a containing this resin pillar 10. As shown in FIG.

  The insulating layer 1b laminated on the upper and lower surfaces of the core body 1a has a thickness of about 20 to 50 μm, and has a plurality of via holes 11 having a diameter of about 30 to 100 μm from the upper surface to the lower surface of each layer. These insulating layers 1b are provided to provide an insulating interval for wiring the wiring conductors 2 at a high density. The insulating layer 1b is covered with a part of the wiring conductors 2 on the surface and in the via holes 11. It is worn. A high-density wiring can be formed three-dimensionally by electrically connecting the upper wiring conductor 2 and the lower wiring conductor 2 via the inner wall of the via hole 11.

  Such an insulating layer 1b is formed by sticking an uncured thermosetting resin film having a thickness of about 20 to 50 μm to the upper and lower surfaces of the core body 1a, thermosetting it, and drilling the via hole 11 by laser processing. Further, it is formed by sequentially stacking the next insulating layer 1b in the same manner. The wiring conductor 2 deposited on the surface of each insulating layer 1b and the via hole 11 has a thickness of about 5 to 50 μm on the surface of each insulating layer 1b and the via hole 11 every time each insulating layer 1b is formed. It is formed by depositing a copper plating film in a predetermined pattern by a pattern forming method such as a known semi-additive method or subtractive method.

  Further, a solder resist layer 7 is deposited on the outermost insulating layer 1b. The solder resist layer 7 is made of an insulating material in which, for example, an inorganic powder filler such as silica or talc is dispersed in an acrylic-modified epoxy resin in an amount of about 30 to 70% by mass, and improves the electrical insulation reliability between the wiring conductors 2 on the surface layer. The function is to increase the bonding strength of the connection pads 2a and 2b described later to the insulating substrate 1.

  Such a solder resist layer 7 has a thickness of about 10 to 50 μm, and an uncured resin paste for the solder resist layer 7 having photosensitivity is applied to the outermost insulating layer by using a roll coater method or a screen printing method. It is formed by coating on 1b and drying it, and then exposing and developing to form openings that expose the connection pads 2a, 2b and marks 3, and then thermally curing them. Alternatively, after an uncured resin film for the solder resist layer 7 is stuck on the uppermost insulating layer 1b, it is thermally cured, and then laser is moved to a position corresponding to the connection pads 2a, 2b and the mark 3. By irradiating light and partially removing the cured resin film, the connection pads 2a, 2b and the mark 3 are formed to have openings.

  The wiring conductor 2 formed from the upper surface to the lower surface of the insulating substrate 1 functions as a conductive path for connecting each electrode of the semiconductor element 8 to the external electric circuit substrate, and the portion exposed on the upper surface of the insulating substrate 1 is A connection pad 2a for connecting an electronic component to which each electrode of the semiconductor element 8 is connected via a solder 4 is connected to an external electric circuit board via a solder ball 12 at a portion exposed on the lower surface of the insulating substrate 1. A connection pad 2b for connection is formed.

  Solder 4, 5 made of lead-free solder such as tin-silver alloy or tin-silver-copper alloy is welded to the connection pads 2a, 2b, thereby causing discoloration and oxidation of the connection pads 2a, 2b. In addition to being prevented, the bonding of each electrode of the semiconductor element 3 and the connection pad 2a via the solder 4 and the bonding of the connection pad 2b and the external electric circuit board via the solder ball 12 are facilitated. Note that the upper end of the solder 4 is higher than that of the solder resist layer 7 in order to improve the connection with each electrode of the semiconductor element 7. Moreover, although it is preferable that the solder 5 is usually lower than the solder resist layer 7, it may be the same height as the solder resist layer 7 or higher. In this example, the solder 5 is welded to the connection pad 2b. However, the solder 5 is not necessarily welded to the connection pad 2b. Instead of welding the solder 5, for example, nickel plating and gold plating are sequentially performed. It may be coated.

  Further, on the upper surface of the insulating substrate 1, there is provided an electronic component positioning mark 3 formed of the same conductor layer as the conductor layer constituting the connection pad 2a. The mark 3 serves as a reference for aligning the electrode of the semiconductor element 8 and the connection pad 2a when the semiconductor element 8 is mounted. For example, the mark 3 has a cross shape, an L shape, a T shape, or a circular shape when viewed from above. The whole is exposed in the opening of the solder resist layer 7. Such a mark 3 is formed at the same time as the connection pad 2a by a method similar to that when forming the connection pad 2a on the upper surface of the insulating substrate 1, that is, a semi-additive method or a subtractive method.

  Furthermore, the mark 3 has a solder 6 having the same composition as the solder 4 deposited on the surface thereof at a height lower than that of the solder resist layer 7. The solder 6 functions to prevent discoloration and oxidation of the mark 3 and to increase the contrast between the mark 3 and its surroundings.

  Then, the mark 3 to which the solder 6 is welded is recognized by an image recognition device, and the electrode of the semiconductor element 8 and the connection pad 2a are aligned by an automatic machine based on the information, and then the melting temperature of the solder 4 By heating to the above temperature, the electrode of the semiconductor element 8 and the solder bonding pad 2 a are bonded via the solder 4.

  At this time, if the height of the solder 6 is set lower than the height of the solder resist layer 7, the solder 6 does not contact the semiconductor element 8 when the semiconductor element 8 is mounted, and the semiconductor element 8 is unnecessary. Contamination can be prevented. Therefore, the height of the solder 6 is preferably set lower than the height of the solder resist layer 7.

  If the thickness of the solder 6 welded to the mark 3 is less than 1 μm, the mark 3 cannot be satisfactorily covered and there is a risk that the mark 3 will be discolored. Therefore, the thickness of the solder 6 welded to the mark 3 is preferably 1 μm or more.

  Next, a method of welding the solder 4 and the solder 6 to the connection pad 2a and the mark 3 of the wiring board according to the manufacturing method of the present invention will be described by taking as an example the case of welding the solder 5 to the connection pad 2b.

  First, as shown in FIG. 2A, a low-viscosity first solder paste 21 having a viscosity of 30 to 150 Pa · s is applied to the mark 3 provided on the upper surface of the insulating substrate 1 by screen printing using a metal mask. To print. A solder paste 22 having the same composition and viscosity is also printed on the connection pads 2b for external connection provided on the lower surface of the insulating substrate 1. The first solder paste 21 contains a lead-free solder powder such as a tin-silver alloy or tin-silver-copper alloy, a flux, and a diluent. The viscosity of the first solder paste 21 can be reduced to a low viscosity of 30 to 150 Pa · s. By printing the low-viscosity first solder paste 21 having a viscosity of 30 to 150 Pa · s on the mark 3 in this way, the surface of the mark 3 can be uniformly covered with a small amount of the thin first solder paste 21. . In addition, when the viscosity of the first solder paste 21 is less than 30 Pa · s, the first solder paste 21 greatly bleeds when printing the first solder paste 21, and it becomes difficult to print well. On the other hand, if it exceeds 150 Pa · s, the viscosity of the first solder paste 21 is so high that it is difficult to spread, so it is difficult to cover the surface of the mark 3 with a small amount of the first solder paste 21. Therefore, the viscosity of the first solder paste 21 is preferably in the range of 30 to 150 Pa · s. In this example, the composition and viscosity of the solder paste 22 are the same as those of the first solder paste 21, but the composition and viscosity of the solder paste 22 may be different from those of the first solder paste 21.

  Next, as shown in FIG. 2B, the solder powder in the first solder paste 21 and the solder paste 22 is heated and melted to weld the solder 6 to the mark 3 and the solder 5 to the connection pad 2b. Let At this time, the first solder paste 21 printed on the mark 3 has a low viscosity, is printed thinly and uniformly, and contains a lot of flux. Therefore, when the solder in the first solder paste 21 is melted, It spreads thinly and uniformly on the surface of the mark 3, and a thin solder 6 having a uniform thickness is deposited on the surface of the mark 3. If the height of the solder 6 deposited on the mark 3 is set lower than the height of the solder resist layer 7, the solder paste 23 for the solder 4 is printed on the connection pad 2a as will be described later. In addition, the printing is not hindered, and the solder 6 does not contact the semiconductor element 8 when the semiconductor element 8 is mounted on the wiring board obtained by the present invention. Can be prevented. Therefore, the height of the solder 6 welded to the mark 3 is preferably set lower than the height of the solder resist layer 7. The solder 5 deposited on the connection pad 2b is usually preferably lower than the solder resist layer 7, but may be the same height as the solder resist layer 7 or higher. Further, if the thickness of the solder 6 welded to the mark 3 and the solder 5 welded to the connection pad 2b is less than 1 μm, the mark 3 and the connection pad 2b cannot be satisfactorily covered. There is a risk of discoloration of the connection pad 2b. Therefore, the thickness of the solder 6 welded to the mark 3 and the solder 5 welded to the connection pad 2b is preferably 1 μm or more.

  Next, as shown in FIG. 2C, a second solder paste 23 having a higher viscosity than the first solder paste 21 is printed on the connection pad 2a by screen printing using a metal mask. The second solder paste 23 contains the same solder powder, flux, and diluent as those contained in the first solder paste 21, and the amount of flux and diluent is less than that of the first solder paste 21. By doing so, the viscosity can be increased. At this time, since the viscosity of the second solder paste 23 is higher than that of the first solder paste 21, it is easy to maintain the shape of the printed second solder paste 23. Therefore, the second solder paste 23 is printed thickly on the connection pad 2a. Can do. Therefore, as described later, when the solder in the second solder paste 23 is heated and melted to weld the solder 4 to the connection pad 2a, the solder 4 having a sufficient height can be welded. When the viscosity of the second solder paste 23 is less than 160 Pa · s, it becomes difficult to print the solder paste 23 having a sufficient thickness on the connection pad 2a. When the solder paste 23 is printed, the removal of the paste from the metal mask becomes worse, and it tends to be difficult to print a uniform amount of the solder paste 23. Therefore, the viscosity of the second solder paste 23 is preferably 160 to 450 Pa · s.

  Finally, as shown in FIG. 2D, the solder powder in the second solder paste 23 is heated and melted to weld the solder 4 to the connection pad 2a. At this time, since the second solder paste 23 printed on the connection pad 2a has a higher viscosity than the first solder paste 21 and is printed thicker, if the solder in the second solder paste 23 melts, the connection A sufficiently high solder 4 can be deposited on the pad 2a. When the solder 4 deposited on the connection pad 2a has a height from the surface of the solder resist layer 7 of less than 5 μm, the electrode of the semiconductor element 8 is mounted when the semiconductor element 8 is mounted on the wiring board obtained by the present invention. There is a tendency that it is difficult to firmly connect the connection pad 2a and the connection pad 2a via the solder 4. On the other hand, when the thickness exceeds 80 μm, there is a high risk that the melted solder 4 contacts and is electrically short-circuited. Therefore, the height of the solder 4 is preferably 5 to 80 μm higher than the surface of the solder resist layer 7.

  Thus, according to the method for manufacturing a wiring board of the present invention, the image recognition apparatus can accurately recognize the mark 3 on which the solder 6 having a thin and uniform thickness is welded, and the electrode of the semiconductor element 8 and the connection pad 2a. Can be provided through the solder 4 having a sufficiently high height.

  Note that the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention. For example, in the above-described embodiment, the electronic component Although the entire positioning mark 3 is exposed from the opening of the solder resist layer 7, the outer periphery of the mark 3 may be covered with the solder resist layer 7. In addition, although the insulating substrate 1 is formed of a material obtained by impregnating a glass fabric with a thermosetting resin and a thermosetting resin, the insulating substrate 1 may be formed of another insulating material such as a ceramic material. .

It is sectional drawing which shows an example of the wiring board manufactured by the manufacturing method of this invention. (A)-(d) is sectional drawing for every process for demonstrating the manufacturing method of the wiring board of this invention.

Explanation of symbols

1: Insulating substrate 2: Wiring conductor 2a: Connection pad to which electrodes of electronic component 3 are connected via solder 4: Marks for positioning electronic components 4, 6: Solder 21: First solder paste 23: Second Solder paste

Claims (1)

After printing the first solder paste on the electronic component positioning mark formed by the conductor layer on the surface of the insulating substrate, the solder in the first solder paste is heated and melted to weld the solder to the mark. A second pad having a viscosity higher than that of the first solder paste on a connection pad formed on the surface of the insulating substrate by the same conductor layer as the mark and to which an electrode of an electronic component is connected via solder. A method of manufacturing a wiring board, comprising: printing a solder paste; and heating and melting the solder in the second solder paste to weld the solder to the connection pad.

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