JPH0927678A - Method of mounting component on printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a mounting operation lessened in man-hours and thermal load by a method wherein cream solder is fed to pads and through-holes located on the one side of a wiring board, surface-mount components are fixed by adhesive agent, then solder is fed to pads and through-holes located on the other side of the wiring board, surface-mount components and insertion mount components are preliminarily fixed, and solder on both sides of the board is made to reflow at the same time. SOLUTION: Gream solder is printed on pads 34 and through-holes 32 through a squeegee printing method making the rear side b of a printed wiring board 30 face upwards, a thermosetting adhesive agent 38 is applied between the pads 34, a surface- mount component 40 is pressed against the adhesive agent 38 aligning its electrodes and fixed by heating carried out at 150 deg.C or so by a heater 50. Then, the wiring board 30 is turned upside down to make its front side a face upwards, cream solder is applied onto the front side a, a surface-mount component 46 is preliminarily fixed to pads 42, and an insertion mount component 48 is preliminarily fixed to through-holes 42, and both sides of the printed board 30 are heated at 230 deg.C or so by a heater 50 to make solders 36 and 46 reflow. By this setup, a mounting operation small in number of man-hours, high in productivity, and low in thermal load can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a component mounting method for a printed wiring board in which surface mount components and lead-insertion mount components are mounted together.

[0002]

2. Description of the Related Art Flow soldering methods and reflow soldering methods are widely known as methods for soldering surface mount type components and insertion mount type components to a printed wiring board. In the flow soldering method, molten solder is poured into the soldering part on the lower surface of the printed wiring board for soldering.In the case of surface mount type parts, it is fixed with an adhesive, and in the case of insert mount type parts, it is fixed. Insert the component leads into the through holes from the top and solder.

The reflow soldering method is applied to surface mount type components, and cream solder is applied to pads (soldering points) in advance, and the viscosity of the cream solder is used with the surface on which the cream solder is applied facing up. And temporarily fix the parts. Then, after that, the cream solder is heated and melted by a heater for soldering.
On the other hand, in recent years, in order to increase the mounting density, a printed wiring board on which an insertion mounting type component and a surface mounting type component are mixedly mounted has been used. In this case, conventionally, soldering is generally performed by the following two methods.

(1-A) to (1-D) of FIG. 6 are views showing a soldering step of the first method. Also, FIGS.
(2-A) to (2-M) are views showing a soldering step of the second method.

First, the first method will be described with reference to FIG. In this method, first, the cream solder 5 is supplied to the pad 3 formed on the upper surface (front surface a) of the printed wiring board 1 by the printing method ((1-A) in FIG. 6). The surface mount type component 6 is temporarily fixed to the pad 3 on the upper surface of the printed wiring board 1 by aligning the electrodes at both ends thereof. That is, the surface mount type component 6 is temporarily fixed by the viscosity of the cream solder 5 itself.

The printed wiring board 1 on which the surface mount type component 6 is mounted is heated by the heater 7 (about 230 ° C.) to melt the cream solder 5. Thereafter, the molten solder is solidified to complete the soldering of the surface-mounted component 6 on the surface a ((1-B) in FIG. 6).

Next, the front and back of the printed wiring board 1 are turned upside down, and the adhesive 8 is applied by a dispenser or the like between the pads 4 formed on the back surface b of the printed wiring board 1 with the back surface b facing upward. The surface mount type component 9 is attached to the pad 4.
Is mounted, the adhesive 8 is cured by heating (about 150 ° C.) by the heater 10, and the surface-mounted component 9 is temporarily fixed ((1 · C) in FIG. 6).

Next, the front and back of this printed wiring board 1 are turned over again so that the surface a becomes the upper surface, and the leads of the insertion mounting type component 11 are provided with through holes 2 formed in the printed wiring board 1.
Align and insert. The printed wiring board 1 is transferred to the molten solder bath 13, and the molten solder comes into contact with the lower surface (rear surface b) of the printed wiring board 1 so that the molten solder is sucked up into the through holes 2 and, at the same time, the surface mount type component 9 Solder is also supplied to the electrode and the pad 4. As a result, the surface mount type component 6 and the insertion mount type component 11
The soldering of the back surface b of is completed.

Next, the second method will be described with reference to FIGS. In this method, first, as shown in (2-A) of FIG. 7, the cream solder 18 is applied to the pad 16 formed on the back surface b of the printed wiring board 15 by a printing method as shown in (2-B) of FIG. Is supplied. This pad 16, 16
The adhesive 19 is applied by a dispenser or the like (see FIG. 7).
(2-C)), the surface mount type component 20 includes the pads 16 and 16
And is bonded to the adhesive 19. Then, the adhesive 19 is cured by heating (about 150 ° C.) by the heater 21 and the surface mount type component 20 is temporarily fixed (see FIG. 7 (2-
D)). At this time, the cream solder 18 does not melt.

Next, the printed wiring board 15 is turned upside down so that the surface a is the upper surface ((2-E) in FIG. 8 and the cream solder 23 is printed on the pads 22 formed on the surface a of the printed wiring board 15. Is supplied by ((2-
F)). The surface mount type component 20 is the cream solder 2
It is temporarily fixed to this pad 22 by utilizing the viscosity of 3 ((2-G) in FIG. 8).

In this way, the printed wiring board 15 having the surface-mounted components 20 mounted on the front and back surfaces a and b is the heater 2
Heated by 1 (about 230 ℃) cream solder 18,
25 is melted. Solidification of the melted solder completes soldering on both the front and back surfaces of the surface-mounted component 20 ((2-H) in FIG. 8).

Next, the printed wiring board 15 is turned upside down so that the back surface b is the upper surface ((2-I) in FIG. 9) and the cream solder 24 is dispensed into the through holes 17 formed in the printed wiring board 15 by a dispenser. It is applied ((2-J) in FIG. 9). The front and back of the printed wiring board 15 are inverted again ((2-K) in FIG. 9), the surface a is made the upper surface, and the lead of the insertion mounting component 25 is inserted into the through hole 17 ((2-L) in FIG. 9). ).

In the printed wiring board 15 on which the insertion mounting type component 25 is mounted, only the vicinity of the lead of the insertion mounting type component 25 on the lower surface (rear surface b) is locally heated by the hot air discharged from the nozzle 26. . As a result, the cream solder 24 is melted and the melted solder is solidified, whereby the soldering of the insertion mounting type component 25 is completed ((2-M) in FIG. 9).

[0014]

2. Description of the Related Art As described above, the two conventional methods are to separately solder the insertion mount type component after the reflow soldering of the surface mount type component. Therefore, there is a problem that the number of soldering steps increases.

The first method also requires a molten solder bath for flow soldering in addition to the device for reflow soldering. Similarly, in the second method, not only the cream solder is supplied by the printing method, but also a dispenser is required to supply the cream solder to the through holes, and further, the cream solder is locally heated and melted. A hot air nozzle is also required.
Therefore, in the two conventional methods, the device becomes large in scale,
There was also a problem that its management became troublesome.

Further, in the first conventional method, since the printed wiring board is passed through the molten solder bath after the reflow soldering, the printed wiring board is heated twice. In the second method, the through-hole portion is locally heated after the reflow soldering. When the number of times of heating is increased in this way, thermal stress is applied to the printed wiring board due to the heat load, which may cause deformation such as warpage or twisting of the printed wiring board or deterioration of product quality.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and can reduce the number of steps to improve productivity, eliminates the need for a large-scale device, and reduces the heat load applied to a printed wiring board. An object of the present invention is to provide a component mounting method for a printed wiring board which is reduced in number and suitable for improving product quality.

[0018]

According to the present invention, an object of the present invention is to mount a surface mounting type component on both sides of a printed wiring board and a lead insertion mounting type component in a through hole by soldering. Simultaneously supplying cream solder to the pads and through-holes for surface-mounted components on one surface of the printed wiring board by a printing method,
After fixing the surface mount type component to this same surface with an adhesive, cream solder is simultaneously supplied to the surface mount type component pad and the through hole on the other side of the printed wiring board by a printing method, and the surface is coated on this side. This is achieved by a method for mounting a component on a printed wiring board, characterized in that a mountable component and an insert mountable component with leads are placed and temporarily fixed with cream solder, and the cream solders on both sides are simultaneously reflow-soldered.

In the metal mask used for printing the cream solder, it is desirable to provide a blind portion having a diameter smaller than that of the through hole at a position corresponding to the vicinity of the center of the through hole. This blindfold portion can be provided with a function of facilitating insertion of the lead of the insertion mounting type component and appropriately managing the total amount of cream solder supplied to the through holes from both sides. The adhesive is a thermosetting adhesive that cures at a lower temperature than cream solder.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Steps A to H shown in FIGS. 1 and 2 show a soldering step according to the present invention. Printed wiring board 30
1A, through holes 32 are formed as shown in FIG. 1A, and pads 34 and 42 are formed on the back surface b and the front surface a. A metal mask (not shown) is placed on the surface b with the back surface b of the printed wiring board 30 facing upward, and the openings of the metal mask are aligned with the pads 34 and the through holes 32. Then, after the cream solder 36 is printed by a printing method using a squeegee, the metal mask is lifted and peeled off. Then, the pad 34 of the printed wiring board 30
And the amount of cream solder 36 corresponding to the thickness of the metal mask is printed on the through hole 32 ((B) of FIG. 1).

Next, a thermosetting adhesive 38 is applied between the pads 34, 34 by a dispenser or the like (see FIG. 1).
(C)). The electrodes of the surface mount component 40 are aligned with the pads 34, 34 and the component 40 is pressed against the adhesive 38. In this state, the whole is heated by the heater 50 (about 150
℃). The temperature of the heater 50 (about 150 ° C.) is sufficient to cure the adhesive 38, but not so high as to melt the cream solder 36. The cream solder 36 used here is preferably one that melts at about 230 ° C. The surface mount type component 40 is temporarily fixed to the pads 34, 34 by the curing of the adhesive 38 ((D) of FIG. 1).

Next, the printed wiring board 30 is turned over so that the surface a is the top surface (FIG. 1 (E)). Then, a metal mask (not shown) is placed on the printed wiring board 30, the openings are aligned with the pads 42 and the through holes 32, and cream solder is printed with a squeegee. If the metal mask is lifted and peeled off, the cream solder 44 in an amount corresponding to the thickness of the metal mask is supplied to the pads 42, 42 and the through hole 32 of the printed wiring board 30 as in the case of the back surface b (FIG. 1 (F)). ).

Next, the surface mount type component 46 is temporarily fixed to the pad 42 on the surface a of the printed wiring board 30 by the cream solder 44, and the lead of the insert mount type component 48 is inserted into the through hole 32 so that the cream solder 44 is formed. , 36
To be temporarily fixed ((G) in FIG. 2). After that, the cream solders 36 and 46 are melted by heating (about 230 ° C.) with the heater 50. If the molten solder solidifies, the surface mount type components 40, 46 on the printed wiring board 30 will be described.
And the soldering of the insertion mounting type component 48 is completed ((H) of FIG. 2).

In order to solder the insertion mount type component 48, cream solder 36, 44 is formed in the through hole 32 from both the front surface a and the rear surface b of the printed wiring board 30.
Is printed. In this case, it is desirable to use a metal mask 52 as shown in FIG. Although only the opening 54 corresponding to the through hole 32 is shown in the metal mask 52, it goes without saying that the metal mask 52 actually also has an opening corresponding to the pads 34 and 42.

A circular blind portion 56 is provided at the center of the opening 54. The blind portion 56 is held at the inner peripheral edge of the opening 54 by a pair of support portions 58, 58. It is preferable that the blind portion 56 has a diameter substantially equal to the lead diameter of the insertion mounting component 48 to prevent the cream solder from adhering to the lead when the insertion mounting component 48 is mounted.

The amount of cream solder 36, 44 supplied by the printing method depends on the thickness of the metal mask used. Therefore, if the thickness of the metal mask is determined so that the supply amount to the pads 36 and 42 is optimal, the cream solder 36 supplied from both surfaces a and b to the through hole 32,
The total supply amount of 44 may be inappropriate. Therefore, it is desirable to determine the diameter of the blind portion 56 in consideration of the supply amount to the through hole 32.

[0027]

EXAMPLE A concrete example of the present invention using this metal mask will be described below with reference to FIGS. FIG. 4 is a sectional view schematically showing a soldering state of the through hole portion, and FIG. 5 is a plan view (A) and a side sectional view (B) showing a state of supplying the cream solder to the through hole portion.

The components of the cream solder used here are as shown in Table 1 below.

[0029]

[Table 1] Volume ratio Specific gravity Content weight ratio ─────────────────────────── Flux 39% 1.0 7% Sn / Pb 61% 8.4 93%

When this cream solder is used, even if it contains a flux of 7% by weight before reflow, it is volatilized and disappears after reflow, and the volume is reduced to about 61% compared to before reflow. . In consideration of this, first, the minimum amount of cream solder required to obtain the shape of FIG. 4 after solidification is determined.

In FIG. 4, the volume V of the solder is the volume of the cylindrical portion within the thickness of the printed wiring board 30.
This volume V can be calculated by the following equation.

[0031]

## EQU1 ## V = πt (R ² −r ² )

However, t is the thickness of the printed wiring board 30 (= 1.6 mm), 2R is the diameter of the through hole 32 (=
0.8 mm), 2r is a lead 48a of the insertion mounting type component 48
Is the diameter (= 0.6 mm).

When the volume V is calculated by substituting the above numerical values,
V = 0.35 mm ³ . Therefore, the volume V ′ of the cream solder before reflow is V ′ = V × 100/61 = 0.57.
It becomes mm ³ . Next, a specific example of the opening 54 of the metal mask 52 used for supplying the cream solder having the volume V will be described with reference to FIG.

The cream solder is supplied under the following conditions. The metal mask 52 is used for the insertion mounting type component 48.
The one having the blind portion 56 substantially equal to the lead diameter is used. The opening diameter of the metal mask is 2X (= 1.4 mm-1.
6 mm) and the width of the support portion 58 is Z (= 0.2 mm),
The diameter of the blind portion 56 of the metal mask 52 is set to 2r '(=
0.6 mm), the front surface a and the back surface b are printed once. In this case, it is assumed that the cream solder does not flow into the through hole 32.

Under the above conditions, the thickness = H of the metal mask for supplying the required cream solder amount V ′ = 0.57 mm ³ is calculated by the following formula.

[0036]

[Number 2] H = V '/ 2π (X 2 -r' 2) [mm]

Diameter 2X of opening 54 of metal mask 52
Is 1.6 mm, H = 0.57 / 2π (0.
8 ² −0.3 ² ) = 0.16 [mm]. When the diameter 2X of the opening 54 of the metal mask 52 is 1.4 mm, H = 0.57 / 2π (0.7 ² −0.3 ² ) = 0.
It becomes 23 [mm]. As described above, when the cream solder is printed on the through holes using the method of the present invention, the thickness of the metal mask becomes 0.16 mm to 0.23 mm, and the thickness of the conventional metal mask is sufficient.

At this time, the blindfold portion 5 serves as a bridge for the metal mask on the through hole 32 of the printed wiring board 30.
Since the width of the supporting portion 58 that supports 6 is extremely small, the cream solder wraps around the supporting portion 58 during printing. Therefore, the influence of the support portion 58 does not have to be considered so much in the calculation. Further, it goes without saying that the metal mask 52 has openings 54 corresponding to the through holes 32 and openings corresponding to the pads 34 and 42.

The opening 54 facing the through hole 32 is not limited to a circular shape and may be a square shape or the like. The opening 54 is larger than the diameter of the through hole 32 so that the cream solders 36 and 44 are placed on the pads at both ends of the through hole 32. When the cream solders 36 and 44 are melted, they are sucked into the through holes 32 due to the surface tension or the capillary phenomenon, and the state becomes similar to that of FIG.

[0040]

As described above, according to the first aspect of the present invention, when the cream solder is supplied to the pad on the back surface by the printing method, the cream solder is also supplied to the through holes, and the surface mount type component is provided on this surface. After temporarily fixing with an adhesive, cream solder is applied to the pads and through holes by printing, with the front side facing up, like the back side. Then, an insertion mounting type component and a surface mounting type component are mounted on this surface, and both front and back surfaces are simultaneously subjected to reflow soldering.

Therefore, the cream solder for soldering the surface mount type component and the insertion mount type component can be supplied in the same process, and the components on both sides can be reflow soldered at the same time. The number is reduced and productivity is improved. Further, equipment such as a molten solder bath, a dispenser for supplying cream solder, and a special heater for local heating are not required, and daily management and maintenance are significantly simplified. Furthermore, since the number of times the printed wiring board is heated is reduced, the heat load applied to the printed wiring board is reduced, and there is no risk of quality deterioration such as warping or twisting of the printed wiring board due to repeated heating, which is suitable for quality improvement.

A blind part is provided in the opening of the metal mask for supplying the cream solder to the through hole, and a small hole is formed by the blind part in the cream solder supplied from the opening. Is desirable (claim 2). This is because, when the lead of the insertion mounting type component is inserted into this small hole, there is no risk that the cream solder will adhere to the lead and fall off. It is desirable to provide this blind portion on both sides of the metal mask, but it may be provided only on one surface, especially on the surface opposite to the mounting surface of the insertion mounting type component.

As the adhesive used for the temporary fixing of the surface mount type component, a thermosetting type resin that cures at a temperature sufficiently lower than that of the cream solder is suitable (claim 3).

[Brief description of drawings]

FIG. 1 is a process explanatory view of one embodiment of the present invention.

FIG. 2 is a process explanatory view of one embodiment of the present invention.

FIG. 3 is a diagram showing an opening for a through hole of a metal mask.

FIG. 4 is a cross-sectional view schematically showing a soldering state of a through hole portion.

FIG. 5 is a plan view (A) and a side sectional view (B) showing a solder supply state in a through hole portion.

FIG. 6 is a diagram showing a first conventional method.

FIG. 7 is a diagram showing a second conventional method.

FIG. 8 is a diagram showing a second conventional method.

FIG. 9 is a diagram showing a second conventional method.

[Explanation of symbols]

 30 printed wiring board 32 through hole 34, 42 pad 36, 44 cream solder 38 adhesive 40, 46 surface mounting type component 48 insertion mounting type component 52 metal mask 54 opening 56 blindfold 58 support

Claims (3)

[Claims] 1. A component mounting method for a printed wiring board, wherein surface mount components are soldered on both sides of the printed wiring board, and lead-insertion mount components are soldered on through holes, respectively. Cream solder is simultaneously supplied to the pads for surface mount type components and through holes by a printing method, and the surface mount type components are fixed to the same surface with an adhesive, and then the surface mount type components on the other surface of the printed wiring board. Cream solder is simultaneously supplied to the pads and through holes by the printing method, and the surface mount type component and the insertion mount type component with lead are placed on this surface and temporarily fixed with cream solder, and the solder paste on both sides is reflow soldered at the same time. A method for mounting a component on a printed wiring board, the method comprising: 2. The component mounting of a printed wiring board according to claim 1, wherein the metal mask used for printing the cream solder is provided with a blind portion having a diameter smaller than that of the through hole at a position corresponding to the vicinity of the center of the through hole. Method. 3. The method of mounting a component on a printed wiring board according to claim 1, wherein the adhesive is a thermosetting adhesive that is hardened at a temperature lower than the melting temperature of the cream solder.