JP2004314601A - Metal mask and lead-free solder paste printing method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize excellent soldering by preventing the reduction of connection strength caused by the deterioration (oxidization) of a flux in a lead-free solder paste printing method using the solder including tin as the main component and silver, the solder including tin as the main component and silver and copper or the like. <P>SOLUTION: A circuit substrate (2) is provided with an electrode (21) for connecting the tip part of the lead member (6). Two openings (11a, 11b) are formed at the position corresponding to the position of the electrode (21) on the circuit substrate (2) to a metal mask (1). The shapes of the two openings (11a, 11b) are respectively circular or elliptical. Two lead-free solder paste patterns (30a, 30a), which are arranged in the direction of pulling out from the electrode (21) to the other circuit, are printed by using the metal mask (1). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

 The present invention relates to a metal mark and a method for printing a lead-free solder paste using the same.

  As a method of performing reflow soldering of electronic components and lead members on a circuit board using a conventional tin-lead solder paste, a method shown in FIG. 6 is known (for example, Patent Document 1). First, as shown in FIG. 6A, a metal mask (1) having an opening (11) at a portion corresponding to the position of the electrode (21) of the circuit board (2) is prepared. The metal mask (1) is mounted on the circuit board (2) as described above, and the tin-lead solder paste (3) is placed on the metal mask (1). Next, the printing squeegee (4) is moved from one end of the metal mask (1) to the other end. As a result, the opening (11) is filled with the tin-lead solder paste (3). Then, by peeling off the metal mask (1), a tin-lead solder paste pattern (3a) is printed over the electrode (21) on the circuit board 2 as shown in FIG. 6 (c). Thereafter, as shown in FIG. 6 (d), the electronic component (5), the lead member (6) and the like are placed on the tin-lead solder paste pattern (3a) printed on the circuit board (2) and reflowed. Solder is passed through the furnace.

  As a material of the printing squeegee (4), urethane, metal, or the like is used. When a material made of urethane is used, the urethane is scraped off at an edge portion of the metal mask and the like. Because of the problem of remaining, metal-made materials are often used.

  In recent years, circuit boards used in electronic devices have been demanded to have high performance, multifunctionality, and miniaturization. For this purpose, it is necessary to mount many electronic components on the boards. For the reflow soldering, the above-mentioned tin-lead-based solder paste has been often used.

  However, since lead is a toxic heavy metal, when used electronic devices and mounted circuit boards are not properly disposed of and are dumped in the natural world, the lead becomes a soluble lead compound due to acid rain and flows out, There is a problem that it not only adversely affects the global environment but also flows into groundwater and the like, affecting animals and plants and the human body. Therefore, the use of lead-free solder containing no lead is strongly required.

  Accordingly, lead-free solders such as tin-silver, tin-silver-copper, tin-bismuth, tin-zinc, and tin-antimony have been developed, and solder pastes containing such lead-free solders have been used. Has become. In particular, in a tin-silver-based solder or a tin-silver-copper-based solder, silver is stable, so that the same level of reliability as conventional can be ensured even when used in place of the tin-lead-based solder.

  Such a lead-free solder paste is produced by mixing a flux with a lead-free solder powder containing tin as a main component. However, while the melting point of tin-lead solder is about 183 ° C., the melting point of lead-free tin-silver and tin-silver-copper solder is as high as 220 ° C., so that tin-lead solder is used. When the used flux is used, in the reflow soldering process, the flux volatilizes before the high melting point solder, so that good soldering cannot be performed.

Therefore, tin-silver-based, tin-silver-copper-based solder as a flux used for high melting point lead-free solder paste, based on rosin or modified rosin, solvent, activator, thixotropic agent and other A compound obtained by blending additives is generally used (for example, Patent Document 2).
JP-A-2002-362003 (page 2, FIG. 3) JP-A-2003-10996 (page 2)

  When a high melting point lead-free solder paste such as tin-silver or tin-silver-copper is printed on a circuit board, a rectangular opening provided in a metal mask (1) as shown in FIG. After filling the lead-free solder paste in (11), large frictional heat is likely to be generated between the metal printing squeegee (4) and the metal mask (1) as shown in FIG. In addition, since the shape of the opening (11) is rectangular, the flowability of the filled lead-free solder paste is poor, and the temperature of the lead-free solder paste tends to be increased particularly at the edge portion (15). However, the flux used in the lead-free solder paste has the property of undergoing a chemical change and being deteriorated (oxidized) when exposed to a high temperature, so that the frictional heat causes the flux to be severely deteriorated (oxidized). As a result, solder wettability decreases. As a result, there is a problem that the connection strength between a large component such as a lead member and the circuit board is significantly reduced, and the component is detached from the circuit board due to external pressure and stress.

  Further, when the opening (11) of the metal mask (1) becomes large, it becomes difficult to uniformly fill the opening (11) with the solder paste. Also, as shown in FIG. 6 (d), after the components are placed on the solder paste pattern (3a) printed on the substrate (2), the solder paste is melted by passing through a reflow furnace, and the substrate is melted. (2) In the reflow step of soldering the component on the upper part, there is a problem that the component moves due to the self-alignment effect due to the melting of the solder paste and is shifted from a predetermined position.

  Accordingly, an object of the present invention is to reduce the deterioration of the flux due to frictional heat even when a high melting point lead-free solder paste such as tin-silver or tin-silver-copper is used, in view of the above problems. An object of the present invention is to provide a metal mask capable of performing reflow soldering and a solder paste printing method using the same.

  The metal mask according to the present invention is for applying a lead-free solder paste on the electrodes of the predetermined pattern, for a circuit board on which electrodes for connecting the leading ends of the lead members are formed in a predetermined pattern. At the position corresponding to the position of the electrode on the circuit board, two openings are formed in which the lead member is arranged in the direction in which the lead member is drawn out from the electrode toward another circuit. It is characterized by being circular or elliptical.

  The lead-free solder paste printing method according to the present invention includes disposing the metal mask of the present invention on a circuit board and moving a printing squeegee along the upper surface of the metal mask, thereby pressing the lead-free solder paste against the metal mask. Then, the lead-free solder paste is printed on electrodes of a predetermined pattern formed on the circuit board through openings formed in the metal mask.

  Here, the lead-free solder paste includes a solder having a melting point higher than 183 ° C., and the circuit board includes an electrode to which a lead member for electrically connecting to another circuit is connected. The two lead-free solder paste patterns are printed side by side in the direction in which the lead member is pulled out from the electrode toward another circuit, and the shape of each of the lead-free solder paste patterns is circular or elliptical.

  By using the lead-free solder paste printing method according to the present invention, it is possible to reduce the frictional heat between the printing squeegee and the metal mask, and improve the flowability of the solder paste inside the opening of the metal mask, A rise in the temperature of the solder paste due to frictional heat can be suppressed. As a result, it is possible to prevent a decrease in connection strength due to deterioration (oxidation) of the flux and to perform good soldering.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the solder paste printing method using a metal mask according to the present invention, a lead-free solder paste containing solder having a melting point higher than 183 ° C., for example, a lead-free solder containing tin-silver or tin-silver-copper solder is used. Paste is used. In such a lead-free solder paste, since silver is stable, even if it is used instead of a tin-lead-based solder, it is possible to secure the same level of reliability as before.

  As shown in FIG. 4, in the metal mask (1) according to the present invention, the lead member (6) is provided at a position corresponding to one electrode (21) on the circuit board to which the lead member (6) is to be connected. Two openings (11, 11) arranged in the direction of being drawn out from the electrode (21) are provided, the area of each opening (11) is made smaller than the conventional opening, and the shape of each opening (11) is formed in an elliptical shape. are doing.

  As shown in FIG. 5, in another metal mask (1) according to the present invention, the lead member (6) is placed at a position corresponding to one electrode (21) on the circuit board to which the lead member (6) is to be connected. ) Are provided from the electrode (21) and four openings (11, 11, 11, 11) arranged in a direction perpendicular to the direction, and the area of each opening (11) is made smaller than that of the conventional opening. Each opening (11) is formed in a circular shape.

  FIG. 1 shows the steps of the solder paste printing method of the present invention. In this step, a metal mask (1) shown in FIG. 2 is used. The metal mask (1) has two elliptical openings corresponding to one electrode (21) on the circuit board to which the lead member (6) is to be connected and arranged in the direction in which the lead member is pulled out from the electrode. (11a, 11b) are provided. Of these two openings (11a, 11b), the area of one first opening (11a) located on the tip side of the lead member is formed smaller than the area of the other second opening (11b), The ratio of the area S1 of the opening (11a) to the area S2 of the second opening (11b) is set to S1: S2 = 1: 2.

  Further, the two openings (11a, 11b) are formed such that both ends in a direction orthogonal to the lead-out direction of the lead member (6) protrude from the electrode (21) on the circuit board in the direction. Dimension A is set to 0.3 to 0.5 mm. The second opening (11b) is formed such that the end of the lead member (6) on the drawing direction side protrudes from the electrode (21) on the circuit board in the direction, and the protruding dimension B is 0.3. It is set to 0.5 mm. Further, the distance C between the two openings (11a, 11b) is set to 0.3 to 0.4 mm.

  As shown in FIG. 1A, first, the above-described metal mask (1) having two openings (11a, 11b) is prepared at a position corresponding to the position of the electrode (21) of the circuit board (2). The metal mask (1) is mounted on the circuit board (2) as shown in FIG. Next, a tin-silver-copper lead-free solder paste (30) is placed on the metal mask (1), and the printing squeegee (4) is moved from one end of the metal mask (1) to multiple ends. Thus, the openings (11a, 11b) of the metal mask (1) are filled with the lead-free solder paste (30).

  After that, the metal mask (1) is peeled off from the circuit board (2). As a result, a lead-free solder paste pattern (30a) is printed on the electrodes (21) of the circuit board (2) as shown in FIG. 1 (c). Thereafter, as shown in FIG. 1 (d), the electronic component (5), the strip-shaped lead member (6) and the like are placed on the solder paste pattern (30a) on the electrode (21) and passed through the inside of the reflow furnace. Perform soldering. In the reflow furnace, the solder paste is melted, and the solder paste applied outside the electrode falls within the range of the electrode.

  According to the above-described lead-free solder paste printing method, it becomes easy to uniformly fill the openings (11a, 11b) of the metal mask (1) with the lead-free solder paste. Further, the frictional heat generated between the edge (15) of the opening (11) of the metal mask (1) and the metal printing squeegee (4) conventionally shown in FIG. In addition, the fluidity of the lead-free solder paste (30) in the opening is improved, and a rise in the temperature of the lead-free solder paste (30) can be suppressed.

  In addition, as shown in FIG. 2, the first opening (11a) and the other second opening (11b) located on the distal end side of the lead member (6) have a second opening (11b) where external pressure and stress act greatly. ) Is formed to be larger than the area of the first opening (11a), and the solder paste is protruded from the electrode to perform pattern printing. Therefore, even if the lead member is moved by the self-alignment effect during the reflow process, the lead member is still connected. Since a sufficient amount of solder paste can be supplied to the end of the electrode to which a large pressure and stress is applied from the outside in the lead member lead-out direction and to both ends in the direction perpendicular to the lead member lead-out direction, a large connection Strength can be secured. As a result, the connection strength between the lead member (6) and the circuit board increases, and the lead member (6) hardly comes off from the circuit board.

  Also, the area ratio between the first opening (11a) and the second opening (11b), that is, the area ratio between the first printed portion and the second printed portion of the lead-free solder paste formed by these openings is 1: 1.5 to 1.5. It is desirable to set the ratio in a range of 1: 3. When the area of the first printing section is large beyond this range, the difference between the area of the first printing section and the second printing section becomes small, and the pressure from the outside is reduced. On the other hand, the effect of improving the connection strength cannot be sufficiently obtained. If the area of the second printed portion is larger than this range, the lead-free solder paste is uniformly applied because the area of the second opening (11b) is large in the step of applying the lead-free solder paste to the circuit board using a printing squeegee. And the connection strength decreases as a result.

  In a configuration in which two openings are provided in the metal mask in a direction orthogonal to the lead member lead-out direction, a sufficient amount of stress is applied to the end of the electrode where a large stress is applied from the outside when the lead member is connected. Since the solder paste cannot be supplied, the effect of improving the connection strength may not be obtained.

  In the lead-free solder paste printing method of the present invention, since a small gap is provided in the gap between the two openings (11a, 11b) formed in the metal mask (1), the transferability of the solder paste during printing, that is, The metal mask has good removability. Of course, two lead-free solder paste patterns (30a, 30a) are formed on one electrode (21) by the metal mask (1), and a slight gap is formed between the two patterns (30a, 30a). Therefore, gas generated at the time of soldering passes through this gap and is smoothly discharged.

  As described above, according to the lead-free solder paste printing method using the metal mask of the present invention, even when a high melting point lead-free solder paste such as tin-silver or tin-silver-copper is used, a printing squeegee and metal The heat of friction with the mask can be reduced, the fluidity of the solder paste inside the opening of the metal mask can be improved, and the temperature rise of the solder paste due to the heat of friction can be suppressed. As a result, a decrease in the connection strength due to the deterioration (oxidation) of the flux is prevented, and good soldering can be performed.

  It should be noted that the configuration of each part of the present invention is not limited to the above-described embodiment, and various modifications possible by an expert in the technical field can be made without departing from the spirit of the present invention. For example, even if two openings (11a, 11b) opened in the metal mask (1) are connected to each other on each side as shown in FIG. 8, the same effect can be obtained. I can do it. In addition, the shape of the opening of the metal mask according to the present invention includes not only a circular or elliptical shape but also a shape substantially equivalent to a circular or elliptical shape, which provides an effect equivalent to that of a circular or elliptical shape.

It is a series of perspective views showing steps of a lead-free solder paste printing method concerning the present invention. It is a top view of the metal mask in an example. It is a top view of the conventional metal mask. FIG. 3 is a plan view of a metal mask provided with two elliptical openings for one electrode. It is a top view of the metal mask which provided four circular openings on one electrode. It is a series of figures showing a process of a conventional solder paste printing method. FIGS. 3A and 3B are a cross-sectional view and a plan view illustrating a generation of friction between a printing squeegee and a metal mask. FIGS. FIG. 4 is a plan view of a metal mask in which two openings are connected to each other.

Explanation of reference numerals

(1) Metal mask
(11) Opening
(11a) First opening
(11b) Second opening
(15) Edge
(2) Circuit board
(21) Electrode
(3) Tin-lead solder paste
(3a) Tin-lead solder paste pattern
(30) Lead-free solder paste
(30a) Lead-free solder paste pattern
(4) Printing squeegee
(5) Electronic components
(6) Lead member

Claims (13)

For a circuit board (2) in which electrodes (21) for connecting the tips of the lead members (6) are formed in a predetermined pattern, a lead-free solder paste (30) is formed on the electrodes (21) of the predetermined pattern. In a metal mask for applying
At the position corresponding to the position of the electrode (21) on the circuit board (2), two openings (11a, 11a, 11b) are arranged in a direction in which the lead member (6) is drawn out from the electrode (21) toward another circuit. 11b) is formed, and the shape of these two openings (11a, 11b) is circular or elliptical, respectively. The metal mask according to claim 1, wherein the two openings (11a, 11b) each have an elliptical shape having a short axis in a drawing direction of the lead member (6). Of the two openings (11a, 11b), the area of the first opening (11a) located on the tip side of the lead member (6) connected to the electrode (21) of the circuit board (2) is the other. The metal mask according to claim 1 or 2, wherein the area is set smaller than the area of the second opening (11b). The metal mask according to claim 3, wherein an area ratio of the first opening (11a) and the second opening (11b) is set to 1: 1.5 to 1: 3. The two openings (11a, 11b) are formed such that both ends in a direction orthogonal to the drawing direction of the lead member (6) protrude from the electrode (21) on the circuit board (2). The metal mask according to any one of claims 1 to 4, wherein: Of the two openings (11a, 11b), the opening (11b) located in the lead member drawing direction has an end on the lead member drawing direction side from the electrode (21) on the circuit board (2) in the direction. The metal mask according to claim 1, wherein the metal mask is formed so as to protrude. 7. The metal mask according to claim 1, wherein the two openings are connected to each other at respective side portions. 8. A metal mask (1) is set on a circuit board (2) on which an electrode (21) for connecting the leading end of a lead member (6) is formed in a predetermined pattern, and the metal mask (1) is placed on the upper surface of the metal mask (1). A lead-free solder paste printing method for printing by moving the surface of the electrode (21) on the circuit board (2) by moving the printing squeegee (4) along the surface of the electrode (21) on the circuit board (2).
The circuit board (2) includes an electrode (21) for connecting the tip of a lead member (6), and the metal mask (1) has an electrode (21) on the circuit board (2). Two openings (11a, 11b) are formed at positions corresponding to the positions, and the shapes of these two openings (11a, 11b) are each circular or elliptical, and by using the metal mask (1), A lead-free solder paste printing method, comprising printing two lead-free solder paste patterns (30a, 30a) arranged in a direction to be drawn from the electrode (21) to another circuit. Of the two openings (11a, 11b) of the metal mask (2), a first opening (11a) located on the tip side of a lead member (6) connected to an electrode (21) of the circuit board (2). 9. The method for printing lead-free solder paste according to claim 8, wherein the area of the second opening (11b) is smaller than the area of the other second opening (11b). The lead-free solder paste printing method according to claim 9, wherein an area ratio between the first opening (11a) and the second opening (11b) is set to 1: 1.5 to 1: 3. The two openings (11a, 11b) of the metal mask are formed so that both ends in a direction orthogonal to the lead-out direction of the lead member (6) protrude from the electrode (21) on the circuit board (2). The method for printing a lead-free solder paste according to claim 8, wherein: Of the two openings (11a, 11b) of the metal mask, the opening (11b) located in the lead member lead-out direction has an end on the lead member lead-out direction side from the electrode (21) on the circuit board (2). The lead-free solder paste printing method according to any one of claims 8 to 11, wherein the solder paste is formed in a size protruding in the direction. The lead-free solder paste according to any one of claims 8 to 12, wherein the lead-free solder paste (30) is made of solder containing tin as a main component and containing silver, or solder containing tin as a main component and containing silver and copper. Solder paste printing method.

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