JP2007081086A - Metal mask and packaging method of electronic parts - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To hold the bonding strength of electronic parts to a printed circuit suppressing the generation of solder balls, moreover, even when the mounting position of the electronic part is misaligned, and the printing position of cream solder is misaligned. <P>SOLUTION: The packaging method includes a process to superpose a metal mask 1 on a printed circuit board 5; a process to coat by printing W-shaped cream solders 10 whose tops are arranged to be facing opposedly on the one pair of part lands 6, 6 formed in a rectangular shape in the printed circuit; a process to mount the electronic part W on the printed circuit so that the electrodes Wa of the both ends overlap respectively the cream solders on the one pair of part lands; and a process to solder the electronic parts by charging, setting, and warming the electronic parts mounted on the printed circuit by the every printed circuit board in a reflow furnace. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal mask and an electronic component mounting method using the metal mask.

As a method of mounting a chip-type electronic component having electrodes on both left and right ends of a main body, such as a chip capacitor or a chip resistor, on a printed circuit board, conventionally, an opening of a metal mask superimposed on the printed circuit board is used. The solder paste is applied by printing onto a pair of component lands on the printed circuit board, and then the electronic component is mounted on the printed circuit board so that the electrodes at both ends thereof overlap the cream solder on the component land. A method is known in which electronic components mounted on a printed circuit board are set in a reflow furnace together with the printed circuit board and heated to heat the electronic components.
In such an electronic component mounting method, it has been common to apply cream solder on a component land formed on a printed circuit board so as to form a rectangular shape having substantially the same shape as the component land. However, in this case, when the electronic component is mounted on the cream solder, the cream solder protrudes from the side surface of the electronic component, and the excess cream solder that protrudes does not adhere to the electrode when the heat treatment is performed in the reflow furnace. It remains as a solder ball. When this solder ball is detached from the printed circuit board due to vibration or the like, for example, it hits between electrode pins of other electronic components, causing a problem that the electrode pins are short-circuited.

In order to deal with such a problem, in Patent Document 1, cream solder is applied to a pair of component lands so that the corners are arc-shaped by removing the inner corners in a round shape. Has been proposed.
Further, in Patent Document 2, as shown in FIG. 10, cream solder 101 is applied on a pair of component lands 100 so that the inner corners are removed in a triangular shape so that the whole becomes a substantially base shape. It has been proposed to do.
Further, in Patent Document 3, as shown in FIG. 11, on the pair of component lands 100, the entire inner corner portion is removed into a triangular shape and the inner end portion is also excluded. It has been proposed to apply the cream solder 101 in a state of being close to the outside of the land 100. In FIGS. 10 and 11, reference numeral 102 denotes an uncoated portion of cream solder, W denotes an electronic component, and Wa denotes an electrode of the electronic component.
Japanese Patent Laid-Open No. 7-273441 JP-A-5-121868 JP 2000-91739 A

However, the above-described conventional electronic component mounting method has the following problems.
In the electronic component mounting method described in Patent Document 1, cream solder is applied on a pair of component lands except for the inner corners being rounded, but the amount of cream solder applied is still large. In many cases, when an electronic component is mounted so that an electrode is superimposed on the cream solder, the cream solder protrudes from the side surface of the electronic component W, and there is a problem that a desired solder ball reduction effect cannot be obtained.

Further, in the electronic component mounting method described in Patent Document 2, as shown in FIG. 10, since there are wide unapplied portions 102 to which the cream solder 101 is not applied at the inner corners of the component land 100, the cream solder When the electronic component W is mounted on 101, when the electronic component W is mistakenly mounted obliquely from the normal position (see FIG. 10B), the electrode Wa of the electronic component W is applied with the cream solder 101. Even if it overlaps, the area of the overlapping part is extremely small, and the electronic component W is soldered to the printed circuit board while being displaced from the normal position during reflow. It becomes. In this case, since the soldered portion is narrow, there arises a problem that the bonding strength of the electronic component W to the printed circuit board is weakened.
In order to avoid this, the cream solder uncoated portions 102 at the inner corners of the component land 100 may be narrowed. However, in this case, as shown in FIG. As a result, part of the electronic component W protrudes from the side surface of the electronic component W, and eventually, the solder ball 103 is formed. For this reason, the desired solder ball reduction effect cannot be obtained.

  In the electronic component mounting method described in Patent Document 3, as shown in FIG. 11, since there are unapplied portions 102 to which the cream solder 101 is not applied at the inner corner portions and inner end portions of the component land 100, When the electronic component W is mounted on the cream solder 101, as shown in FIG. 11B, when the electronic component W is erroneously mounted obliquely with respect to the normal position, the electrode Wa is cream soldered. There is a problem in that the bonding strength of the electronic component W to the printed circuit board is weakened because it is difficult to overlap the coated portion 101. In addition, when the cream solder 101 is printed on the pair of component lands 100, as shown in FIG. 11C, when printing misalignment occurs in the length direction of the electronic component W, the electrode Wa of the electronic component W is displayed. However, there is a problem that the electronic component W cannot be bonded to the printed circuit board because it does not overlap at all with the portion to which the cream solder 101 is applied.

      The present invention has been made in view of the above-described problems, can suppress the generation of solder balls, and even when the mounting position of the electronic component is shifted or the printing position of the cream solder is shifted, the electronic component It is an object of the present invention to provide a metal mask and an electronic component mounting method capable of ensuring strong bonding strength to a printed circuit board.

The present invention employs the following configuration in order to solve the above problems.
That is, a metal mask according to the present invention includes a pair of openings for printing cream solder for soldering electrodes of electronic components on a pair of component lands each formed in a square shape on a printed circuit board. The pair of openings are formed so as to expose a region excluding the inner corners and the inner middle portion of the pair of component lands when overlaid on the printed circuit board. Features.

  According to the present invention, the cream solder printed by the metal mask is applied to other areas except for both the inner corners and the inner middle part of the pair of component lands, and the cream solder is not applied. Since the portion expands, the uncoated portion absorbs excess cream solder when an electronic component is mounted, and the amount of cream solder protruding from the component land can be suppressed as much as possible. As a result, the generation of solder balls can be suppressed. Also, the cream solder printed by the metal mask is applied to other areas excluding both the inner corners and the inner middle part of the pair of component lands. At the edge, at least one top is formed on each of the left and right sides. For this reason, the top of the inner edge of the cream solder application portion and the electrode of the electronic component can overlap even if there is a position shift when mounting the electronic component or a print shift occurs during cream solder printing As a result, it is possible to secure a high bonding strength of the electronic component to the printed circuit board.

The metal mask according to the present invention is characterized in that inner edges of the pair of openings facing each other are formed in a W shape so that the tops are opposed to each other.
According to the present invention, the cream solder printed by the metal mask is also formed in a W shape with the top portion opposed to each other. Therefore, a wide uncoated portion of the cream solder is ensured while ensuring the required length with respect to the component land. can do.

The metal mask according to the present invention is characterized in that the distance between the base ends of the W-shaped openings formed in the W-shape of the pair of openings is set equal to the length of the electronic component.
According to the present invention, the distance between the top portions of the cream solder coated portions printed by the metal mask is always shorter than the length of the electronic component. For this reason, even if there is a position shift when mounting electronic components, or even when a print shift occurs during cream solder printing, the top of the inner edge of the cream solder application part and the electrode of the electronic component are more reliably connected. Can be overlapped.

The metal mask according to the present invention is characterized in that the top of the W-shaped opening is formed in an arc shape.
According to the present invention, the adhesion of cream solder to the metal mask is weak at the top of the W-shaped opening. Therefore, when the metal mask is peeled off from the printed circuit board after printing, the cream solder once printed on the component land can be prevented from being removed from the component land while adhering to the metal mask.

  In the electronic component mounting method according to the present invention, the above-described metal mask is superimposed on a printed circuit board, and the inner corners and the inner intermediate part on the pair of component lands formed in a square shape on the printed circuit board, respectively. A step of applying cream solder to a region to be removed by printing, and a step of mounting the electronic component on the printed circuit board such that electrodes at both ends thereof overlap with the cream solder on the pair of component lands, And a step of soldering the electronic component by charging the electronic component mounted on the printed circuit board together with the printed circuit board in a reflow furnace and heating it.

  According to the present invention, since the uncoated portion of the cream solder spreads on the component land, the amount of cream solder that protrudes from the component land can be suppressed as much as possible, and therefore, the generation of solder balls can be suppressed. In addition, at least one top part is formed on the inner edge of the cream solder application portion printed by this metal mask, respectively, on the left and right sides. Even if it occurs, there is a high possibility that the top of the inner edge of the cream solder application portion and the electrode of the electronic component overlap, and therefore, the bonding strength of the electronic component can be ensured high.

  According to the present invention, the amount of cream solder protruding from the component land can be suppressed as much as possible, and as a result, the generation of solder balls can be suppressed. In addition, even if there is a misalignment when mounting electronic components, or even when misprinting occurs during cream solder printing, the top of the inner edge of the cream solder coating may overlap with the electrodes of the electronic component. Therefore, strong bonding strength of electronic components to the printed circuit board can be ensured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 is a perspective view of a metal mask, FIG. 2 is a plan view of the metal mask, FIG. 3 is a flowchart showing a procedure of a mounting method of an electronic component using the metal mask, and FIG. 4 is a flowchart of the mounting method of the electronic component. It is a perspective view shown.

  As shown in FIGS. 1 and 4, the metal mask 1 is printed with cream solder 10 for soldering the electrodes Wa of the electronic component W to a pair of component lands 6 and 6 formed in a square shape on the printed board 5. To do. The metal mask 1 includes a pair of openings 2 and 2. The pair of openings 2 and 2 are formed at positions corresponding to the pair of component lands 6 and 6 of the printed circuit board 5. The metal mask 1 is made of, for example, a metal such as stainless steel or nickel, and the thickness thereof is set to about 80 to 200 μm.

  2 and 4, when the metal mask 1 is superimposed on the regular position of the printed circuit board 5, the pair of openings 2 and 2 are provided at the inner corners of the pair of component lands 6 and 6, respectively. The region excluding the corner portion 7 and the inner intermediate portion 8 is formed to be exposed. Specifically, the pair of openings 2 and 2 includes an inner W-shaped opening 3 and an outer rectangular opening 4. Here, the inner side and the outer side are called based on the arrangement of the pair of openings 2 and 2. Moreover, in a pair of opening parts 2 and 2, the vertex of the W-shaped opening part 3 is arrange | positioned at the inner edge part of both the opening parts 2 so that it may mutually oppose.

  As shown in FIG. 2, the distance La between the base end portions 3 a of the W-shaped opening 3 of the pair of openings 2 and 2 is set equal to the length Lb of the electronic component W. The width dimension Ha of one side of the rectangular opening 4 is set substantially equal to the width dimension Hb of the electronic component W and the width dimension of one side of the component land 6. Furthermore, the height of one side of the unevenness of the W-shaped opening 3 is set to ¼ of the width dimension Ha of one side of the rectangular opening 4.

Next, an electronic component mounting method using the metal mask 1 will be described.
First, as shown in FIG. 4, for example, a metal mask 1 is placed on a printed board 5 made of a glass cloth epoxy board or the like, and a pair of openings 2 and 2 of the metal mask 1 are a pair of component lands on the printed board 5. Overlay to match 6,6. Next, the cream solder 10 is supplied to one side of the metal mask 1, and the supplied cream solder 10 is moved on the surface of the metal mask 1 from one side of the metal mask 1 to the other side by a printing squeegee 11, The cream solder 10 is printed on the component land 6 using the openings 2 and 2 (step 1 in FIG. 3).
As the solder solder 10, Sn-Pb, Sn-Ag-Cu, Sn-Ag-In-Bi, Sn-Zn, Sn-Bi, or the like is used. The squeegee 11 is made of rubber or metal.

  Next, the electronic component W is mounted on the printed circuit board 5 so that the electrodes Wa at both ends thereof overlap the cream solders 10 on the pair of component lands 6 and 6 (step 2 in FIG. 3).

  Next, the electronic component W mounted on the printed circuit board 5 is loaded and set in the reflow furnace together with the printed circuit board 5 and heated to a predetermined temperature. Thereby, the cream solder 10 on the component land 6 is heated and melted and flows between the component land 6 and the electrode Wa without any gap so as to be electrically connected. Then, when it cools to predetermined temperature, cream solder solidifies and the soldering with respect to the component land 6 of the electronic component W is completed. (Step 3 in FIG. 3).

Next, when mounting an electronic component also on the back surface side of the printed circuit board 5, the printed circuit board 5 is reversed, and the steps 1 to 3 described above are repeated (steps 4, 5, and 6 in FIG. 3). Electronic components are also mounted on the back side of the printed circuit board.
Thereafter, by mounting necessary post-installation components on the printed circuit board 5 (step 7 in FIG. 3), the mounting of the electronic components on the printed circuit board 5 is completed.

  According to the electronic component mounting method described above on the printed circuit board, the cream solder 10 printed by the metal mask 1 is applied to both the inner corner portions 7 and 7 and the inner intermediate portion 8 of the pair of component lands 6 and 6. It is applied to other areas excluding, and each is formed into a W shape with the tops facing each other.

  For this reason, compared with the conventional electronic component mounting method shown in FIG. 10, the uncoated portion of the cream solder 10 is expanded. When the electronic component W is mounted, this uncoated portion absorbs the excess cream solder that tends to protrude from the side surface of the electronic component W while being crushed by receiving a load (Z region indicated by hatching in FIG. 6). Represents the movement state of the excess cream solder when the electronic component is mounted), and the amount of cream solder protruding from the component land 6 can be suppressed as much as possible. As a result, the generation of solder balls can be suppressed as much as possible.

Further, the cream solder 10 printed by the metal mask 1 is applied to other areas except for both the inner corners and the inner middle part of the pair of component lands 6 and 6 inevitably. In addition, apexes 10a are formed on the left and right sides of the inner edge of the application portion of the cream solder 10, respectively. Moreover, these top portions 10 a are located at the inner edges of the component lands 6 and 6. For this reason, as shown in FIG. 5, even when the positional deviation occurs when the electronic component W is mounted, the top 10 a of the inner edge portion of the application portion of the cream solder 10 and the electrode Wa of the electronic component W overlap. It will be. In this case, the electronic component W is automatically corrected for misalignment due to the wettability and surface tension of the melted cream solder with respect to the electrode Wa and the component land 6 of the electronic component during reflow. Return to. For this reason, the high joint strength to the printed circuit board 5 of the electronic component W is obtained. The same applies to the case where a printing misalignment occurs during cream solder printing.
In addition, the cream solder 10 printed by the metal mask 1 is applied over almost the entire area without forming an uncoated portion in the portion corresponding to the outer region of the pair of component lands 6 and 6. Therefore, as shown in FIG. 4, a sufficient solder fillet 14 is formed, and at the same time, higher bonding strength of the electronic component W to the printed circuit board 5 can be obtained.

  FIG. 7 shows that when the shape of the cream solder printed on the component land is formed in a W shape with the tops facing each other as shown in the above-described embodiment, it is formed in a square shape as described in the prior art. The appearance frequency of the solder balls is compared for each of the cases where the solder balls are formed and the home base. The vertical axis represents the frequency of appearance of solder balls, and the horizontal axis represents what form of cream solder was used.

Here, A is a cream solder formed in a square shape, B is a cream solder formed in a home base shape, and C is a cream solder having a W shape with the tops facing each other as shown in this embodiment. Represents. The experiment was carried out 12 times for each cream solder material.
As is apparent from this figure, in the case where the cream solder indicated by A is formed in a square shape, when Pb is used as the cream solder material, no solder balls appeared, but Sn-Ag- When Cu was used, solder balls appeared 11 times out of 12 times, and when Sn-Ag-Cu-Bi was used as a cream solder material, solder balls appeared 12 times out of 12 times.
Further, in the case where the cream solder indicated by B is formed in a home base shape, when Pb is used as the cream solder material, no solder ball appeared, but when Sn-Ag-Cu was used as the cream solder material When Sn-Ag-Cu-Bi was used as the cream solder material, solder balls appeared 10 times out of 12 times.
On the other hand, in the case where the cream solder indicated by C has a W shape, when Pb is used as the cream solder material, Sn—Ag—Cu— is used as the cream solder material, Sn—Ag—Cu— as the cream solder material. When Bi was used, no solder ball appeared in any case.
From these results, it has become clear that the use of the electronic component mounting method of the present embodiment suppresses the generation of solder balls.

The present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the invention.
For example, in the embodiment, in the W-shaped opening 3 of the opening 2 of the metal mask 1, the lengths of the valleys on both sides and the central valley are made equal, but the present invention is not limited to this. As shown in FIG. 8A, the valleys 21 on both sides may be shallower than the valley 20 on the center, and the center on the valleys 22 on both sides as shown in FIG. 8B. As shown in FIG. 8 (c), the valleys 24 and 25 on both sides and the center may be made shallow together, as shown in FIG. 8 (d). As shown, the left and right top portions 26, 26 may be shifted laterally, and the top portions 27 may be three as shown in FIG. 8 (e). Furthermore, as shown in FIG. 8F, the top 28 and the valley 29 may be formed in an arc shape. This arcuate shape may also be applied to one having three tops as shown in FIG. 8 (e).

Furthermore, in the above-described embodiment, the width dimension of the component land 6 and the cream solder 10 printed thereon is substantially equal to the width dimension of the electronic component W. However, the present invention is not limited to this. 6 and the width dimension of the cream solder 10 printed thereon may be increased by the width dimension of the electronic component W. In this case, as shown in FIG. 9, the solder fillet 14 is formed not only on the end surface of the electronic component W but also on the side surface, and the bonding strength of the electronic component W can be further increased.
Further, the electronic component mounting method according to the present invention is not applied only when a chip-type electronic component is mounted, but can also be applied when mounting other electronic components.

It is a perspective view of the metal mask of the embodiment of the present invention. It is a top view of the metal mask of the embodiment of the present invention. It is a flowchart figure which shows the procedure of the mounting method of the electronic component of embodiment of this invention. It is a perspective view which shows the procedure of the mounting method of the electronic component of embodiment of this invention. It is a top view explaining an effect | action of the mounting method of the electronic component of embodiment of this invention. It is a partial enlarged plan view for explaining the operation of the electronic component mounting method of the embodiment of the present invention. It is a figure showing the comparison with the mounting method of the electronic component of embodiment of this invention, and the mounting method of the conventional electronic component. It is a top view which shows the modification of the metal mask of embodiment of this invention. It is a perspective view explaining the other example of the mounting method of the electronic component of embodiment of this invention. It is a top view explaining the mounting method of the conventional electronic component. It is a top view explaining the mounting method of the other conventional electronic component. It is a top view which shows the problem of the mounting method of the conventional electronic component.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal mask 2 Opening part 3 W-shaped opening part 4 Square-shaped opening part 5 Printed circuit board 6 Component land 7 Inner both corners 8 Inner intermediate part 10 Cream solder

Claims (5)

In a metal mask having a pair of openings for printing cream solder for soldering electrodes of electronic components on a pair of component lands formed in a quadrangular shape on a printed board,
The pair of openings are formed so as to expose a region excluding the inner corner portions and the inner middle portion of the pair of component lands when the printed circuit board is overlaid. Metal mask to be used.       2. The metal mask according to claim 1, wherein inner edges of the pair of openings facing each other are formed in a W shape so that the tops are opposed to each other.   3. The metal mask according to claim 2, wherein the distance between the base ends of the W-shaped openings formed in the W-shape of the pair of openings is set equal to the length of the electronic component.   4. The metal mask according to claim 3, wherein the top of the W-shaped opening is formed in an arc shape. A region excluding the inner corners and the inner intermediate part on a pair of component lands formed in a square shape on the printed circuit board by overlapping the metal mask according to any one of claims 1 to 4 on the printed circuit board And a step of applying cream solder by printing;
Mounting the electronic component on the printed circuit board so that the electrodes at both ends thereof overlap with the cream solder on the pair of component lands,
And mounting the electronic component mounted on the printed circuit board in a reflow furnace together with the printed circuit board to heat the electronic component, and mounting the electronic component.

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