JP4381657B2 - Circuit board and electronic component mounting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit board and electronic component mounting method of the electronic component is mounted.
[0002]
[Prior art]
Solder precoat is widely used as a method for supplying solder when electronic components are mounted on a substrate by solder bonding. In this method, prior to mounting an electronic component on a substrate, a solder layer is formed in advance on a connection electrode provided on the substrate by a method such as solder plating or a solder leveler. Thereby, in the mounting process, it is not necessary to separately supply solder to the electronic component or the substrate, and the component mounting can be performed only by supplying the flux to the joint portion, and there is an advantage that the process is simplified.
[0003]
[Problems to be solved by the invention]
In general, since a large number of electronic components of different sizes and types are mounted on a single circuit board, connection electrodes having shapes and sizes corresponding to the connection terminals of the respective electronic components are mounted on the same circuit board. Is formed. In general, in the formation of a solder precoat, the height of the solder precoat formed on the electrode surface varies depending on the size of the target electrode. When electronic parts are mounted with the solder precoats varying in height and this substrate is sent to reflow, various problems occur. For example, in an electrode having a low solder precoat, the solder may not come into contact with the terminals of the electronic component due to warpage deformation of the substrate, deformation of the lead of the electronic component, and the like, causing a solder joint failure.
[0004]
Accordingly, the present invention aims at providing a beauty electronic component mounting method Oyo circuit board that can prevent failure of the solder joint.
[0005]
[Means for Solving the Problems]
The circuit board according to claim 1 is a circuit board having a plurality of electrode portions for solder-bonding terminals of different types of surface-mounted components, wherein the electrode portions have shapes and sizes of conductive pads and terminals of the surface-mounted components. Correspondingly, a plurality of pattern holes having an area of 0.018 to 2.3 mm ² are formed of a resist layer that partially exposes the upper surface of the conductive pad, and solder precoat is applied to the upper surface of the conductive pad exposed from the pattern hole. The height of the solder precoat was 5 to 6 mm (× 10 ⁻² ) .
[0006]
The electronic component mounting method according to claim 2 is an electronic component mounting method for mounting an electronic component on the circuit board according to claim 1 ,
A thermosetting resin having an oxide film removing function for removing the oxide film on the surface of the solder precoat by adding an active component and applying an active component is applied so as to cover the solder precoat. A step of mounting an electronic component terminal on the solder precoat and holding the terminal by the adhesive force of the thermosetting resin; and heating the circuit board by sending the circuit board to a reflow process. The solder precoat is melted to form a molten solder, and the molten solder is wetted and spread on the joint surface of the terminal, and the thermosetting resin is simultaneously heated to activate the active component, thereby The oxide film present on the surface is removed, and the terminal is sucked to the conductive pad by the self-alignment function of the molten solder. And aligning the thermosetting resin along the lower surface of the terminal to form a resin fillet between the resist layer and the lower surface of the terminal, and further heating to step a including that by advancing the thermosetting reaction of the thermosetting resin was completely cured the thermosetting resin forming the adhesive resin layer.
[0016]
According to the present invention, the area of 0.018～2.3Mm ² plurality of electrodes of a circuit board surface mounted components are mounted, the area of the specific range a stable solder height in solder precoat formation is obtained formed with a fine pattern, by solder bonding the terminals of the surface mount components by soldering these fine patterns, by eliminating variations in solder height due to the difference in electrode size, failure of the solder joint Can be prevented.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. 1 is a perspective view of a circuit board according to an embodiment of the present invention, FIG. 2 is a perspective view of an electrode portion of the circuit board according to an embodiment of the present invention, and FIG. 3 is a circuit board according to an embodiment of the present invention. FIG. 4 is a graph showing the relationship between the solder height and the pattern area in one embodiment of the present invention, and FIGS. 5 and 6 are electronic component mountings in one embodiment of the present invention. FIG. 7 is a perspective view of a mounted circuit board according to an embodiment of the present invention.
[0018]
First, a circuit board and electronic components mounted on the circuit board will be described with reference to FIGS. In FIG. 1, electrode portions 2, 3, 4, and 5 for mounting different types of surface-mounted components are provided on the upper surface of the circuit board 1. One terminal 12a, 13a, 14a, 15a of the electronic components 12, 13, 14, 15 which are surface mount components is soldered to the electrode portions 2, 3, 4, 5 respectively.
[0019]
The electronic components 12 and 13 are both rectangular chip-type components, and are provided with two terminals 12a and 13a having different sizes. The electronic component 14 is an SOP IC component and includes a lead-type terminal 14a extending to the side. The electronic component 15 is a cylindrical capacitor component, and a flat terminal 15a is provided on the bottom surface. In the present embodiment, any one of the electronic components 12, 13, 14, and 15 corresponds to the first surface mount component and the second surface mount component, respectively. That is, at least a first surface mount component and a second surface mount component are mounted on the circuit board 1 by solder bonding. The electrode portions to which the terminals of the first surface mount component and the second surface mount component are soldered correspond to the first electrode portion and the second electrode portion.
[0020]
Next, the configuration of the electrode part on which the electronic component is mounted will be described. The electrode portions 2 to 5 each have a micro-diameter pattern 2b in which the upper surface of the conductive pad is partially exposed on the conductive pads 2a to 5a disposed on the upper surface of the resin substrate 1a of the circuit board. It is the structure which formed ~ 5b. When the electronic component is mounted on the circuit board 1, soldering is performed between the terminals of the electronic component and the conductive pads by supplying solder to these patterns. In the present embodiment, solder precoats S2 to S5 are formed in advance on these patterns to supply solder.
[0021]
The size of these conductive pads 2a to 5a corresponds to the size of the terminal to be connected, and there are combinations of patterns of different sizes and numbers corresponding to the sizes of the conductive pads 2a to 5a. Selected. 1 and 2, only the electrode part 5 having the largest size is shown in an enlarged manner, but the other electrode parts have the same configuration.
[0022]
FIG. 2A shows the electrode portion 5 before the solder precoat is formed. On the resin substrate 1a, a conductive pad 5a that is electrically connected to the wiring pattern 5c is formed in a planar shape substantially equal to the terminal 15a of the electronic component 15 to be connected. The electrode part 5 is covered with a resist layer 1b, and a pattern 5b in which the upper surface of the conductive pad 5a is exposed is formed by forming a minute pattern hole in the resist layer 1b on the conductive pad 5a. Then, as shown in FIG. 2B, a solder precoat S5 is formed on the pattern 5b.
[0023]
Here, with reference to FIG. 3, a combination example of the size and number of patterns provided in each electrode portion will be described. 3 (a), (b), (c), and (d) show the combinations of patterns in the electrode portions 2, 3, 4, and 5 and the height of the solder precoat formed on each pattern, respectively. . As shown in FIG. 3A, only one pattern 2 b having a hole diameter d <b> 2 is provided on the conductive pad 2 a of the electrode portion 2. Such an electrode part is applied when the terminal to be connected has a circular or substantially square shape and a very small size, such as a microchip component (electronic component 12). Then, a solder precoat S2 having a solder height H2 from the upper surface of the conductive pad 2a is formed on the pattern 2b.
[0024]
FIGS. 3B and 3C show a case where a terminal to be connected has an elongated rectangular shape such as a terminal of a relatively large chip component (electronic component 13) or a lead of an SOP type IC (electronic component 14). The example of the electrode part is shown. On the conductive pads 3a and 4a of the electrode parts 3 and 4, two patterns 3b and 4b having hole diameters d3 and d4 are provided in the longitudinal direction, respectively. On the patterns 3b and 4b, solder precoats S3 and S4 having solder heights H3 and H4 from the upper surfaces of the conductive pads 3a and 4a are formed.
[0025]
Further, FIG. 3D shows an electrode portion when the dimension in the width direction as well as the longitudinal direction is large like the terminal of the cylindrical capacitor component (electronic component 15). Three patterns 5b having a hole diameter d5 are provided on the conductive pad 5a of the electrode part 5, and a solder precoat S5 having a solder height H5 from the upper surface of the conductive pad 5a is formed on the pattern 5b.
[0026]
That is, the electrode portion formed on the circuit board 1 is configured by an aggregate in which micropatterns are combined according to the shape and size of the terminal to be connected. In the above example, a circular pattern with a small diameter is used as the micro pattern. However, the micro pattern is not limited to a circular shape, and can be regarded as a dot shape such as a rectangle or a polygon excluding an elongated slit shape. If it is.
[0027]
Next, with reference to FIG. 4, the relationship between the solder height of the solder precoat formed in the pattern formed in each electrode part as described above and the pattern area will be described. FIG. 4 shows a result obtained by actually forming a solder precoat on a pattern having a different pattern area (circular shape) on a conductive pad and measuring the height with respect to the pattern area in the same manner as the circuit board 1 shown in FIG. This is a graph showing the relationship between the solder heights, and the pattern area on the horizontal axis is a logarithmic scale.
[0028]
As can be seen from the graph of FIG. 4, in the range where the pattern area is very small, the solder height is small because the solder hardly enters the pattern and the amount of adhesion to the conductive pad is small. On the other hand, when the pattern area is large, the solder spreads well on the surface of the conductive pad, so the solder height becomes low. On the other hand, when the pattern area is in a specific range, that is, when the pattern area is in an appropriate pattern area range to obtain a higher solder height, a stable solder height is obtained.
[0029]
Specifically, when the pattern area is in the range R1 of 0.018 to 2.3 mm ² , the solder height is in the range of 5 to 6 mm (× 10 ⁻² ), which is practically acceptable. Solder height can be stabilized. Furthermore, when the pattern area is in the range R2 of 0.07 to 0.64 mm ² , the solder height is constant at 5 mm (× 10 ⁻² ), and a more stable solder height can be obtained. I understand.
[0030]
Therefore, in the circuit board 1 shown in the present embodiment, a plurality of electrode portions provided for connecting terminals of a plurality of types of surface mounting components including at least the first surface mounting component and the second surface mounting component. (Including a first electrode portion to which one terminal of the first surface mount component is connected by solder bonding and a second electrode portion to which one terminal of the second surface mount component is connected by solder bonding ) Is formed of an assembly of minute patterns having an area of 0.018 to 2.3 mm ² .
[0031]
Next, an electronic component mounting method for manufacturing a mounted circuit board by mounting a plurality of surface mount components on the circuit board 1 by solder bonding will be described with reference to FIGS. Here, of the electrode portions formed on the circuit board 1, only the electrode portion 4 is illustrated and described, but the same process is executed in the other electrode portions.
[0032]
First, the circuit board 1 shown in FIG. 1 is prepared. The plurality of electrode portions provided on the prepared circuit board 1 include an electrode portion 4 in which a pattern 4b is formed in the resist layer 1b on the conductive pad 4a, as shown in FIG. 5A. Yes. Next, as shown in FIG. 5B, a solder precoat S4 is formed on the pattern 4b. As a solder precoat forming method, a method such as solder plating or solder leveler is used.
[0033]
Thereafter, as shown in FIG. 5C, a thermosetting resin 6 such as an epoxy resin is applied so as to cover the solder precoat S4. Here, the resin 6 has a curing timing later than the melting timing of the solder, and uses a resin that does not hinder the self-alignment function by the molten solder in the reflow process, as will be described later.
[0034]
Further, an active component such as an organic acid is added to the resin 6 and has an oxide film removing function for removing the oxide film on the surface of the solder precoat S4. As a result, good solderability can be ensured without separately supplying a flux during soldering.
[0035]
Next, a plurality of electronic components are mounted on the circuit board 1. These electronic components include the electronic component 14, and the terminals 14 a of the electronic component 14 are mounted on the plurality of solder precoats S 4 constituting the electrode portion 4 as shown in FIG. . As a result, as shown in FIG. 6A, the terminal 14 a lands on the solder precoat S <b> 4 through the resin 6 and is held by the adhesive force of the resin 6. Along with this mounting operation, terminals of electronic components to be connected are mounted on the other electrode portions, respectively.
[0036]
Next, the circuit board 1 after the electronic components are mounted is sent to a reflow process, where the circuit board 1 is heated. As a result of this heating, as shown in FIG. 6B, the solder precoat S4 is first melted to become the molten solder S4 *, and spreads on the joint surface of the terminal 14a. At this time, the resin 6 is heated at the same time, whereby the active component in the resin 6 is activated by heating and exhibits an oxide film removing function. Thereby, the oxide film present on the surface of the solder precoat S4 is removed, and good wettability with the terminal 14a is ensured.
[0037]
In this reflow process, at the timing when the solder precoat S4 is melted, the resin 6 has not yet undergone thermosetting, and the viscosity is lowered by heating and the fluidity is increased. Therefore, the resin 6 does not hinder the self-alignment function of the molten solder S4 *, and the terminal 14a is aligned so as to be attracted to the conductive pad 4a by the surface tension of the molten solder S4 *. At this time, as the fluidity of the resin 6 increases, the resin present in the vicinity of the bent portion of the terminal 14a crawls up along the lower surface of the terminal 14a, and the resin fillet is formed between the resist layer 1b and the lower surface of the terminal 14a. Part 6a is formed.
[0038]
And heating is continued further after this and the thermosetting reaction of the resin 6 progresses when the temperature of the resin 6 rises. When the resin 6 is completely cured, an adhesive resin layer of the cured resin 6 * is formed on the lower surface of the terminal 14a as shown in FIG. 6C. This adhesive resin layer is also present between the patterns 4b, so that the terminal 14a is cooled and solidified by the molten solder S4 * of the solder precoat, and the cured resin 6 on the lower surface side of the terminal 14a. It is firmly fixed to the circuit board 1 with the adhesive resin layer by *. Therefore, even when the terminals are soldered via a minute pattern, a mounting structure having sufficient adhesive strength is realized.
[0039]
Thereby, the mounted circuit board 1A shown in FIG. 7 is completed. As described in the mounting process, the mounted circuit board 1A mounts a plurality of electronic components 12, 13, 14, 15 including at least a first surface mount component and a second surface mount component by solder bonding. Of these electronic components, one terminal of the first surface mount component is connected to the first electrode portion by solder bonding, and one terminal of the second surface mount component is soldered to the second electrode portion. It is connected by joining.
[0040]
The first electrode portion and the second electrode portion of these are formed in the aggregate of fine patterns having an area of 0.018～2.3Mm ^2, the plurality of fine patterns constituting the first electrode portion One terminal of the first surface mount component is joined with the solder of the first surface mount component, and one terminal of the second surface mount component is joined with the solder on the plurality of minute patterns constituting the second electrode portion. Yes.
[0041]
As described above, according to the present invention, the electrode portion of the circuit board is formed by an aggregate of minute patterns having an area in a specific range in which a stable solder height can be obtained in forming the solder precoat. Accordingly, it is possible to easily perform land design of a circuit board on which a plurality of types of surface mount components having different shapes and sizes of connection terminals are mounted, and in the manufacturing process, the entire circuit board 1 is targeted. The required amount of solder can be collectively supplied to each electrode part by a single solder precoat forming step.
[0042]
In addition, the solder precoat formed on the electrode part is formed on a minute pattern, so the total surface area is small, and when using lead-free solder that is susceptible to surface oxidation due to atmospheric exposure, This is a desirable solder supply form. Furthermore, in the solder supply by printing cream solder on the upper surface of the electrode, as the electrode becomes smaller, the cream solder tends to sag, and it is difficult to cope with micro-sized parts. Since it is a method of forming a solder precoat, there is an advantage that solder can be supplied stably even with a fine electrode.
[0043]
In the above-described embodiment, an example in which the resin 6 is applied on the solder precoat is shown, but a strong adhesive flux may be applied without using the resin 6. As a result, good solderability can be ensured, and the electronic component can be held by the adhesiveness of the flux until the post-mounting reflow process.
[0044]
【The invention's effect】
According to the present invention, an electrode portion of a circuit board in which a plurality of types of surface mount components are mounted, the 0.018～2.3Mm ² is the area within a specific range a stable solder height in solder precoat formation is obtained formed with fine patterns of the area, since the terminals of the surface mount components by soldering these fine pattern so as to solder joint, to eliminate variations in solder height due to the difference in electrode size, the solder Bonding defects can be prevented.
[Brief description of the drawings]
FIG. 1 is a perspective view of a circuit board according to an embodiment of the present invention. FIG. 2 is a perspective view of an electrode portion of the circuit board according to the embodiment of the present invention. FIG. 4 is a graph showing the pattern arrangement of the electrode portion of the substrate. FIG. 4 is a graph showing the relationship between the solder height and the pattern area in the embodiment of the invention. FIG. 5 is a process of the electronic component mounting method in the embodiment of the invention. Explanatory drawing [FIG. 6] Explanatory drawing of process of electronic component mounting method of one embodiment of the present invention [FIG. 7] Perspective view of mounted circuit board of one embodiment of the present invention
DESCRIPTION OF SYMBOLS 1 Circuit board 1A Mounted circuit board 2,3,4,5 Electrode part 2a, 3a, 4a, 5a Conductive pad 2b, 3b, 4b, 5b Pattern 6 Resin 12,13,14,15 Electronic component 12a, 13a, 14a 15a Terminals S2, S3, S4, S5 Solder precoat

Claims (2)

In a circuit board having a plurality of electrode portions for soldering terminals of different types of surface mount components, the electrode portions correspond to the shape and size of the terminals of the conductive pads and the surface mount components, 0.018 to 2.3 mm. a plurality of pattern holes having a ^second area is formed in the resist layer to the upper surface partially exposed in the conductive pads, said exposed from the pattern hole to form a solder precoat on the upper surface of the conductive pads, high of the solder precoat A circuit board having a thickness of 5 to 6 mm (× 10 ⁻² ) . An electronic component mounting method for mounting an electronic component on the circuit board according to claim 1,
A thermosetting resin having an oxide film removing function for removing the oxide film on the surface of the solder precoat by adding an active component and applying an active component is applied so as to cover the solder precoat. A step of mounting an electronic component terminal on the solder precoat and holding the terminal by the adhesive force of the thermosetting resin; and heating the circuit board by sending the circuit board to a reflow process. The solder precoat is melted to form a molten solder, and the molten solder is wetted and spread on the joint surface of the terminal, and the thermosetting resin is simultaneously heated to activate the active component, thereby The oxide film present on the surface is removed, and the terminal is sucked to the conductive pad by the self-alignment function of the molten solder. And aligning the thermosetting resin along the lower surface of the terminal to form a resin fillet between the resist layer and the lower surface of the terminal, and further heating to An electronic component mounting method comprising a step of forming an adhesive resin layer by causing a thermosetting reaction of a thermosetting resin to proceed to completely cure the thermosetting resin.

Images