JPH07235764A - Surface mount method for narrow-pitch parts - Google Patents

Abstract

PURPOSE:To accurately and surely mount narrow-pitch parts on the surface of a substrate. CONSTITUTION:Among pads 4a and 4b which form a row of pads for QFP1 referred-to as narrow-pitch parts, the specific pads 4a are covered with a precoated layer 8 of solder. A cream solder 9 is fed onto the pads 4b other than the pads 4a covered with the layer 8. A bond flux 15 serving as a flux adhesive agent is fed to the pads 4a covered with the layer 8. Then QFP1 is mounted and heated to melt the solder paste 9 and layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a narrow pitch component such as a QFP (Quad Flat Gull Wing Greeded Package) via solder on a substrate having a pad row for mounting the narrow pitch component. Surface mounting method.

[0002]

2. Description of the Related Art In recent years, along with the miniaturization and high performance of electronic devices, it has become popular to mount components such as QFP and chip resistors, so-called SMD (Surface Mount Device), on a wiring board. It is being appreciated. That is, the surface mounting method as described above has an advantage that it is suitable for higher density than the pin insertion mounting method. Further, recently, in order to further increase the mounting density on the substrate, narrowing the pitch of active components such as QFP and increasing the number of pins accordingly are being promoted. Then, how to accurately and surely mount such a narrow pitch component is one of the major problems in the process of manufacturing an electronic device.

Here, an example of a method of surface-mounting the QFP on the substrate will be introduced. Four pad rows are formed on the substrate so as to correspond to one QFP. The number of pads forming the four pad rows depends on the QF to be surface-mounted.
It is the same as the number of P leads. These pads are pre-coated with solder. Examples of the method of coating with solder include a plating method and a printing method. next,
A flux adhesive is applied onto the covered pad by a dispensing method or the like. Flux adhesives are fluxes that are slightly more viscous (viscosity is several hundred cps) than ordinary liquid flux. Next, the QFP is mounted on the substrate while positioning. At this time, QFP
The leads are temporarily fixed on the pad by the adhesive force of the flux adhesive. Finally, soldering by reflow soldering is performed to join the QFP leads and pads. After the above procedure, the QFP is surface-mounted on the substrate.

[0004]

However, in the case of the conventional adhesive force of the flux adhesive, there is a problem that the force for holding the lead on the pad is insufficient. Therefore, the temporary fixing position of the QFP is likely to be displaced due to, for example, vibration of the component mounting machine when releasing the board or transfer of the component mounting machine to the soldering device.

The problem caused by such positional deviation tends to become more prominent as the QFP leads have a narrower pitch. Therefore, when a QFP having an extremely narrow pitch of 0.5 mm or less, and further 0.3 mm or less is used, there is a problem that the yield decreases due to frequent mounting defects.

The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide a surface-mounting method for a narrow-pitch component capable of accurately and reliably surface-mounting a narrow-pitch component on a substrate. To provide. The second aspect of the present invention
It is an object of the present invention to provide a surface mounting method for a narrow pitch component which can avoid a short circuit between pads due to a solder bridge.

[0007]

In order to solve the above problems, in the invention described in claim 1, a narrow pitch component is mounted on a substrate having a pad row for mounting the narrow pitch component via solder. In the method of surface mounting, at least one of a specific pad among the pads constituting the pad row, and an external connection terminal of the narrow pitch component corresponding to the specific pad is covered with solder, and the specific pad Supplying the solder paste on pads other than the pads, and in the state of supplying the high-viscosity flux adhesive on at least one of the specific pad and the external connection terminal, connect each external connection terminal of the narrow pitch component. As its gist, the surface mounting method of the cream solder and the narrow pitch component in which the solder is melted by heating after temporarily fixing while positioning on each pad That.

Further, the invention according to claim 2 is, in the invention according to claim 1, characterized in that the cream solder is supplied onto at least two pads which are not adjacent to each other. Further, in the invention according to claim 3, in the invention according to claim 1, the pad row is
A pad row for surface mounting a narrow pitch component having leads on all four side surfaces, and the cream solder is supplied on the outermost pad of the pads constituting each pad row. Is the gist.

[0009]

According to the first aspect of the invention, the external connection terminals of the narrow pitch component are held by not only the adhesive force of the flux adhesive but also the adhesive force of the cream solder.
Therefore, even if the board receives some vibration before it is transferred from the component mounting machine to the soldering machine,
Positional deviation is less likely to occur in the temporarily fixed narrow-pitch component.

According to the second aspect of the present invention, in addition to reducing the positional deviation of the narrow pitch component, the pads to which the cream solder is to be supplied are separated from each other, so that the solder bridge is less likely to occur.

In particular, according to the third aspect of the invention, since the leads held by the cream solder are on all the side surfaces, the narrow pitch component is securely fixed in four directions, and the positional deviation is further increased. Less likely to happen. Moreover, since the pads to which the cream solder is supplied are located on the outermost side of the pad row, the solder bridge becomes even less likely to occur.

[0012]

【Example】

[Embodiment 1] Hereinafter, Embodiment 1 in which the present invention is embodied as a surface mounting method of a narrow pitch component on a printed wiring board will be described with reference to FIGS.
This will be described in detail with reference to FIG.

In the first embodiment, as a narrow pitch component to be mounted, a QFP made of plastic with a pitch of 0.3 mm is used.
1 is selected. The QFP 1 has leads 2a and 2b as external connection terminals on all four side surfaces thereof. The total number of leads 2a and 2b is 512. The leads 2a and 2b have a gull wing shape as shown in FIGS. It should be noted that the QFP1 is shown in a somewhat omitted form for convenience of drawing.

FIG. 1 shows a printed wiring board 3 as a board for mounting the QFP 1. The printed wiring board 3 is a so-called single-sided board having various pads 4a, 4b, 6 on only one side surface of a resin base material. Further, the printed wiring board 3 has a QFP1 mounting area in which the four pad rows 4 are one unit. Pads 4 that form a pad row 4 for surface mounting the QFP 1
a and 4b are the leads 2 protruding from the side surface of the QFP1.
It is arranged so as to correspond to the positions of a and 2b. Therefore, in the first embodiment, the number of pads 4a and 4b forming one pad row 4 is the same as the number of leads 2a and 2b provided on one side surface of the QFP 1 (that is, 128).
Individual).

Pads 4a and 4b constituting the pad row 4
In the case of Example 1, each is 1.0 mm in length × 0.1 in width
It is 8 mm. The distance between the pads 4a and 4b is 0.1.
The pad 4a, 4b has a pitch of 0.3 mm.

On the printed wiring board 3, in addition to the pads 4a and 4b as described above, pads 6 for surface-mounting the chip resistor 5 which is a passive component are also formed. The pad 6 is an electrode 7 as an external connection terminal of the chip resistor 5.
Corresponding to, two units are provided as one unit. The area of the pad 6 is larger than the area of the pads 4a and 4b that form the pad row 4. Pad 6
Similarly, the distance between them is larger than the distance between the pads 4a and 4b forming the pad row 4. In addition,
On the printed wiring board 3, other general-purpose components not shown (for example, wide pitch SOP [Single Outline Package]
Etc.) pads are also formed. A wiring pattern (not shown) is formed on the printed wiring board 3.

Next, the procedure for surface mounting the QFP 1 on the printed wiring board 3 will be described. First, as shown in FIG. 3, the pads 4 constituting the pad row 4 are formed.
Only specific pads 4a of a and 4b, that is, all the pads 4a except the pad 4b located on the outermost side of the pad row 4 are covered with the solder 8 (solder precoat).
Hereinafter, the solder 8 formed as described above will be referred to as a solder precoat layer 8 for convenience of description.

The solder precoat layer 8 is heated after supplying a lead-containing / tin-containing paste onto the pad 4a according to a conventionally known coating method such as a screen printing method, a stencil printing method, a plating method and a dispensing method. Formed by. Here, the lead-containing / tin-containing paste is not limited to a paste containing a lead-tin alloy such as cream solder, but also a paste containing organic acid lead and tin.

In Example 1, as the lead-containing / tin-containing paste, cream solder having a high viscosity of 450,000 cps to 500000 cps (Tamura Corporation, trade name: SQ
-1030SZH-1) 9 is used. The cream solder 9 has an alloy composition of 63 Sn / 37 Pb, a melting point of 183 ° C., a flux content of 10 wt%, a solder grain size of 38 μm to 45 μm, and a solder grain shape of a sphere. Also, this cream solder 9
Also has an excellent plate-through property when continuously printed.

In the first embodiment, the method of forming the solder precoat layer 8 is such that the cream solder 9 is printed by the stencil printing method and then reflowed in the near infrared reflow furnace. In this printing method,
For example, a metal mask 10 made of stainless steel, phosphor bronze, nickel or the like and having a thickness of about 50 μm to 150 μm is used. The metal mask 10 is shown in FIG.
As shown in FIG. 5, a large number of paste supply openings 11 are provided. In the metal mask 10 for forming the solder precoat layer 8 used in Example 1, the openings 11 having substantially the same area as the pad 4a are provided so as to correspond to the positions of the individual pads 4a. The cream solder 9 supplied onto the metal mask 10 is transferred to the surface of the printed wiring board 3 by being pressed with a squeegee.

Solder precoat layer 8 after reflow
Has a thickness of 50 μm to 150 μm, particularly 70 μm to 10 μm
It is preferably about 0 μm. The reason is that if the solder precoat layer 8 becomes too thin, the solder fillet may not be sufficiently formed, and the connection reliability may deteriorate. On the other hand, if the solder precoat layer 8 becomes too thick, a solder bridge may occur, which may cause a short circuit between the adjacent pads 4a. Since the flux component in the cream solder 9 is volatilized through the reflow process, the cream solder 9 is usually printed with a thickness somewhat thicker than the set thickness.

Next, as shown in FIG. 5, the cream solder 9 is placed on the pads 4b other than the specific pads 4a, that is, the pads 4b located on the outermost side of the pad row 4.
To supply. As a supply method in this case, there are conventionally known coating methods such as the above-described screen printing method, stencil printing method, and dispensing method. In Example 1,
Basically, as in the case of forming the solder precoat layer 8, the stencil printing method is adopted as a method of printing the cream solder 9.

FIG. 4 shows the metal mask 12 used in this step. This metal mask 12
A half-etched portion 13 is formed on the back surface side of the pad corresponding to the pad 4a on which the solder precoat layer 8 is formed. The presence of the half-etched portion 13 prevents the solder precoat layer 8 previously formed from being crushed by the back surface of the metal mask 12. In addition, the paste supply opening 14 includes pads 4b other than the pad 4a on which the solder precoat layer 8 is formed,
It is provided so as to correspond to the position of 6. Further, the area of the opening 14 corresponding to the pad 4b located on the outermost side of the pad row 4 is slightly smaller (about 70%) than the area of the pad 4b. This is to prevent the occurrence of solder bridges by setting a small print amount in advance.

The printed thickness of the cream solder 9 is 100 μm or more.
The thickness is preferably 200 μm, particularly about 130 μm to 150 μm. The reason is that if the printing thickness is too small, the lead 2a may not be reliably held during temporary fixing. Further, the solder fillet is not sufficiently formed and the connection reliability may be deteriorated. On the other hand, if the printing thickness is too large, the solder bridge is generated, and the pad 4b and the pad 4a adjacent thereto are formed.
This is because there is a risk that a short circuit will easily occur between and.

Next, as shown in FIG. 6, a bond flux 15 as a flux adhesive is supplied onto the pad 4a on which the solder precoat layer 8 is formed by a dispensing method. In Example 1, “MSP510 flux” (manufactured by Kyushu Matsushita Electric Co., viscosity 6000 cps, which can be applied by drawing) is used as the highly viscous flux adhesive 15 that satisfies the above conditions.

As a means for supplying the bond flux 15, for example, there is a dispenser. The dispenser is required to have good dispensing properties and no sagging. As shown in FIG. 6, in the first embodiment, the bond flux 15 is applied to one character so as to cross substantially the center of each pad 4a.

Next, the printed wiring board 3 is transferred to the component mounting machine. The component mounting machine visually recognizes the mounting position X-
Accurately and quickly mount each component while correcting the Y and rotation directions. As a result, as shown in FIG. 7, both electrodes 7 of the chip resistor 5 are temporarily fixed on the pad 6, and the leads 2a and 2b of the QFP 1 are connected to the pads 4 respectively.
Temporarily fixed on a and 4b.

At this time, first, the surface mount components other than QFP1 (that is, the chip resistor 5, the SOP, etc.) are mounted, and then the narrow pitch component QFP1 is mounted. This is because it is preferable to use such an order in order to prevent the misalignment thoroughly. Note that the QFP 1 to be mounted is selected so that the leads 2a and 2b are as excellent in coplanarity accuracy as possible.

Next, the printed wiring board 3 on which the QFP 1 and the chip parts 5 and the like are mounted is transferred to a near-infrared type reflow furnace and batch reflow soldering (100 ° C. to 160 ° C.) is performed.
Preheat for about 60 seconds and melt at 200 ° C. or higher for 10 seconds).

Then, the cream solder 9 is melted and the solder precoat layer 8 is melted again. Moreover, the bond flux 15 volatilizes by the heat at this time. as a result,
As shown in FIG. 8, each lead 2a, 2b of the QFP 1
And the pads 4a and 4b are joined together, and the electrodes 7 of the chip resistor 5 and the pad 6 are joined together. Through the above procedure, the QFP 1, the chip resistor 5, etc. are surface-mounted on the printed wiring board 3.

Now, the function and effect of the surface mounting method of the QFP 1 on the printed wiring board 3 of the first embodiment will be described. According to this method, not only the adhesive force of the bond flux 15 but also the adhesive force of the cream solder 9 causes the pad 4
The leads 2a and 2b of the QFP 1 are held on the a and 4b. Therefore, even if the printed wiring board 3 is slightly vibrated before being transferred from the component mounting machine to the reflow furnace, the temporarily fixed QFP 1 is less likely to be displaced.

Particularly, according to this method, the cream solder 9
Since there are a plurality of leads 2b held by QFP1 and they are on all sides of QFP1,
Is securely fixed in four directions. Therefore, Q
Positional deviation of FP1 is extremely unlikely to occur, and reflow soldering can be performed in a state where it is temporarily fixed at an accurate position. Therefore, the QFP 1 can be accurately and surely surface-mounted on the printed wiring board 3. That is, the leads 2a and 2b are securely bonded to the predetermined pads 4a and 4b. As a result, mounting defects are reduced and the yield is improved as compared with the conventional case.

Further, according to this method, since the pads 4b to which the cream solder 9 is supplied are sufficiently separated from each other, a solder bridge does not occur between the pads 4b. Of course, this is not only between the pads 4b belonging to the same pad row 4 but also the pads 4b not belonging to the same.
The same applies to spaces. As a result, it is possible to avoid a short circuit between the pads 4b due to the solder bridge.

Particularly in the case of this method, the cream solder 9 is supplied to the outermost pad 4b of the pad row 4. In this case, since the pad 4a exists only on one side of the pad 4b, the probability that a solder bridge will occur between the pad 4a and the pad 4a becomes extremely small. As a result, a short circuit between the pads 4a and 4b due to the solder bridge can be avoided.

According to the method of the first embodiment, QFP1
Since the displacement of the position is prevented, there are the following advantages. That is, since it is possible to withstand vibrations higher than in the past, it is possible to set the operating speed of the conveying means such as a conveyor to be high. Therefore, the time reduction of the entire surface mounting process is achieved.

Further, since the method of the first embodiment employs the batch reflow soldering, there is an advantage that the work efficiency is high and the apparatus is simpler than that in the case of the flow soldering. Further, in the case of this method, the position of the pad 4b to which the cream solder 9 is to be supplied is the pad row 4
Since it is the outermost position, the cream solder 9 can be printed relatively easily. [Embodiment 2] Next, a surface mounting method of the QFP 1 on the printed wiring board 3 of Embodiment 2 will be described with reference to FIGS. 9 to 12.

In the second embodiment, basically, as in the first embodiment, the solder precoat layer 8 is formed on the pad 4a, the cream solder 9 is supplied on the pad 4b, the bond flux 15 is supplied, and the chip component 5 is used. Surface mounting is performed in the order of mounting QFP1, etc. and reflow soldering. Here, the difference from the first embodiment will be mainly described.

In the printed wiring board 20 of the second embodiment, as shown in FIG.
, The pads 4a forming the pad row 4,
Of the pads 4b, the outermost pad 4b is slightly wider than the other pads 4a.

First, the solder precoat layer 8 is formed on the pad 4a provided on the printed wiring board 20.
In Example 2, instead of the stencil printing method of Example 1,
A method of selectively forming solder only on the pads 4a by a precipitation reaction (hereinafter simply referred to as a precipitation reaction method) is adopted. In this method, the paste 21 containing fine tin powder and organic acid lead as main components is used as the lead-containing / tin-containing paste 21. The paste 21 is applied according to a dispenser method, a printing method, or the like, and then heated to a predetermined temperature. As a result, a solder alloy is formed by the precipitation of metallic lead due to the substitution reaction of the fine tin powder in the paste 21 with the organic acid lead and the diffusion of metallic lead into the fine tin powder. The advantages of this precipitation reaction method are that the process is easy and that the film thickness is stable.

In the second embodiment, specifically, "Super Solder FC type coat (trade name: manufactured by Furukawa Electric Co., Ltd.)" is used as the paste 21. Also, as shown in FIG. 9, this paste 2
1 is supplied onto the pad 4a by the dispenser 22. In the second embodiment, the paste 21 is then solidly applied along the pad row 4. Then, the solder precoat layer 8 is formed through heating in a reflow furnace at 210 ° C. for 2 minutes.

Next, the cream solder 9 is supplied by stencil printing to the upper surface of the pad 6 for the chip component 5 and the upper surface of the pad for other general-purpose components. Further, the cream solder 9 is similarly supplied onto the outermost pad 4b of the pad row 4. Note that FIG.
In the second embodiment, the dispenser 23 individually supplies the cream solder 9 onto the pads 4b, as shown in FIG.

Next, the bond flux 15 is supplied in a letter shape on the pad 4a on which the solder precoat layer 8 is formed. Here, as the bond flux 15,
"Finebond BF211 (trade name, manufactured by Furukawa Electric Co., Ltd., viscosity: 150,000 cps)" is used.

Next, the printed wiring board 20 is transferred to a component mounting machine, where each component is mounted. Then, as shown in FIG. 11, the electrode 7 of the chip resistor 5 is temporarily fixed on the pad 6, and each lead 2a, 2b of the QFP 1 is temporarily fixed on each pad 4a, 4b. Hereinafter, batch reflow soldering by a reflow furnace is performed according to the method of the first embodiment. Then, the cream solder 9 melts, the solder precoat layer 8 remelts, and the bond flux 15
Is volatilized by heat. As a result, as shown in FIG. 12, the leads 2a, 2b and the pads 4a,
4b and the electrode 7 of the chip resistor 5 and the pad 6 are joined. By going through the above procedure,
The QFP 1, the chip resistor 5 and the like are surface-mounted on the printed wiring board 20.

Printed wiring board 2 of the second embodiment as described above
Even with the surface mounting method of QFP1 on 0, the same effect as in the first embodiment can be obtained. That is, accurate and reliable surface mounting is achieved by preventing misalignment, the resulting mounting defects are reduced and the yield is improved, and short circuits are avoided by preventing solder bridges between the pads 4a and 4b and between the pads 4a. This includes shortening the time for the entire surface mounting process by allowing higher transport speeds.

Further, according to the second embodiment, since the bond flux 15 having a higher viscosity than that in the first embodiment is used, the lead 2a is more reliably held on the pad 4a, and the temporary fixing is more reliable. Has the advantage that [Third Embodiment] Next, a surface mounting method of the QFP 1 on the printed wiring board 3 according to the third embodiment will be described with reference to FIGS. 13 and 14.

In the third embodiment, the surface mounting is performed in the order of forming the solder precoat layer 8, supplying the cream solder 9 on the pad 4b, supplying the bond flux 15, mounting the chip component 5, QFP1, etc., and reflow soldering. The point to do is
It is common with the first embodiment.

However, as shown in FIG. 13, the solder precoat layer 8 is formed not on the pad 4a but on the tip of the lead 2a of the QFP 1 (that is, the lead other than the lead 2b located at the outermost side). This point is a big difference from the first embodiment.

As a method of forming the solder precoat layer 8 on the tip portion of the lead 2a, for example, there is a method of performing solder plating on the lead 2a while only the lead 2b is protected by a resist. In addition, there is a method of placing a predetermined mask on the tip of the lead 2a in the state of the lead frame, printing cream solder, and heating and melting after lead forming. Also, the lead 2a
There is also a method in which a solder ribbon is applied to the tip of the and the solder ribbon is melted by irradiation with laser light.
When these methods are performed, it is preferable that the thickness of the solder precoat layer 8 is about 70 μm to 100 μm. The reason is as described in detail in the first embodiment.

After that, the pad 4 was prepared according to the procedure of the first embodiment.
The cream solder 9 is applied on the surface b, and the bond flux 15 is supplied on the pad 4a. Then, the printed wiring board 3 is flown to the component mounting machine to mount the QFP 1.
As a result, as shown in FIG. 14, the leads 2a and 2b of the QFP 1 are temporarily fixed on the pads 4a and 4b.
That is, in the case of the third embodiment, the lead 2b located at the outermost side is held by the adhesive force of the cream solder 9, and the other leads 2a are held by the adhesive force of the bond flux 15. Thereafter, the leads 2a and 2b and the pads 4a and 4b are bonded to each other through collective reflow soldering in a reflow furnace.

Printed wiring board 3 of Example 3 as described above
Even with the surface mounting method of the QFP1 on the substrate, the same effects as in the case of the second embodiment can be obtained.
That is, it is possible to realize surface mounting, reduce mounting defects associated therewith and improve yield, avoid short circuits by preventing solder bridges, and shorten the time for the entire surface mounting process by speeding up transportation.

In particular, according to the third embodiment, the elaborate metal mask 10 for printing the solder precoat layer 8 on the printed wiring board 3 becomes unnecessary. Therefore, the workability is improved and the cost is reduced by the amount of time and effort required to manufacture the metal mask 10.

The present invention is not limited to the first to third embodiments, but can be modified as follows. For example, (1) changing the order of the steps of forming the solder precoat layer 8, supplying the solder paste 9 on the pad 4b, supplying the bond flux 15, mounting the chip component 5, the QFP 1, etc., and melting by heating. Is also possible. For example, the bond flux 15 may be supplied before the solder paste 9 is supplied onto the pad 4b.

(2) Outermost pad 4
As a method of supplying the cream solder 9 onto b, for example, there are the following methods. In another example 1 shown in FIG. 15A, the method of linearly supplying the cream solder 9 to the substantially central portion of the pad 4b is adopted. In another example 2 shown in FIG. 15B, a method of linearly supplying the cream solder 9 to a position on the outer side of the pad 4b is adopted. Then, in another example 3 shown in FIG. 15C, the method of supplying the cream solder 9 in a dot shape to the substantially central portion of the pad 4b is adopted.

(3) The cream solder 9 may be supplied onto the adjacent pads 25 as in another example 4 shown in FIG. In the case of the other example 4, both pads (that is, pads other than the specific pad 24) 25 are slightly elongated as compared with the other pads (that is, the specific pad) 24. That is, these pads 25 are provided with the so-called solder escape portions 26 at the tips. In this way, no solder bridge is formed between the pads 25 to which the cream solder 9 is supplied.
Further, as in another example 5 shown in FIG. 16B, the cream solder 9 may be supplied onto the pad 27 having the substantially circular solder escape portion 28. Of course, the shapes of the solder escape portions 26 and 28 are not limited to the above.

(4) An individual soldering method may be used instead of the collective reflow soldering performed in Examples 1 to 4. Examples of individual soldering methods include contact individual mounting using a heat tool or the like, and non-contact individual mounting using a laser or a light beam. The individual soldering method is an effective method, for example, when surface mounting a QFP1 having a lead pitch of 0.2 mm or less.

(5) In the third embodiment, the method of forming the solder precoat layer 8 on both the lead 2a and the pad 4a may be adopted. With this method,
The solder precoat layer 8 can be made thinner than when the solder precoat layer 8 is formed only on either the lead 2a or the pad 4a.

(6) Instead of the reflow method (near infrared method) carried out in Example 1 or the like, for example, a hot air method, a far infrared method, or a combination thereof, or VPS
(Vapor Phase Soldering) method may be adopted.

(7) When the bond flux 15 is supplied onto the pad 4a on which the solder precoat layer 8 is formed,
There is no particular problem if the bond flux 15 covers the pads 4b other than the specific pad 4a. This is because the bond flux 15 is volatilized by the heat during reflow.

(8) In the first embodiment, the opening 11 of the metal mask 10 for forming the solder precoat layer 8 may be replaced with an elongated slit-like opening for printing one character, for example. When it is desired to print only on the pad 4a while avoiding the pad 4b, only the widths at both ends of the opening may be made slightly wider. In this way, the pad 4b
The solder paste 9 can be reliably and easily printed on the pad 4a adjacent to the pad 4a.

(9) From the viewpoint of preventing oxidation of the pads 4a, 4b, 6 and the like, the collective reflow soldering may be performed in an inert atmosphere (for example, in a nitrogen atmosphere) rather than in air. preferable.

(10) When mounting the QFP 1, the bond flux 15 may be applied to the lead 2a side. Of course, it may be applied to both the lead 2a side and the pad 4a side.

Here, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-mentioned embodiments and other examples will be listed below together with their effects. (1) In the invention according to any one of claims 1 and 2, the pads 4b to which the cream solder 9 is to be supplied belong to different pad rows 4. With this method,
Misalignment becomes even less likely to occur.

(2) In any one of claims 1 to 3 and technical idea 1, the cream solder 9 is supplied by a dispensing method. With this method, workability is improved as much as a metal mask for printing is unnecessary.

(3) Claims 1 to 3, technical ideas 1 and 2
In any one of the above, melting of the cream solder 9 and remelting of the solder precoat layer 8 by heating are performed by collective reflow soldering. With this method, work efficiency and device simplification can be achieved.

(4) Claims 1 to 3, technical ideas 1 to 3
In any of the above, the pad 4b located on the outermost side of the pad row 4 is wider than the other pads 4a. In this way, the solder bridge prevention effect is enhanced.

The terms used in this specification are defined as follows. "Narrow pitch parts: QFP (Quad Flat Gull-Wing)
Leaded Package), QFL (Quad Flat L-Leaded Packag
e), QFN (Quad Flat Non-Leaded Package), QTCP
Packages such as (Quad Tape Carrier Package) that have external connection terminals on all four sides, such as BGA (B
uMP Grid Array), LGA (Land Grid Array), surface mount type PGA (Pin Grid Array), etc.
-line Package), TSOP (Thin Small Out-line Packag)
e), packages such as SVP (Surface Vertical Package), etc., and parts made of plastic, metal, ceramics, glass or composite materials thereof. The narrow pitch here is usually 0.5 mm.
Hereinafter, particularly, those having a diameter of 0.3 mm or less. "Pad row: A pad assembly that is arranged in a row or in a zigzag pattern as a conductor portion for connecting leads such as QFP, and is also arranged as a group as a conductor portion for connecting bumps such as BGA. Also referred to as the pad assembly.

[0067]

As described above in detail, according to the invention as set forth in claim 1, the temporarily fixed narrow-pitch component is less likely to be misaligned, so that the narrow-pitch component can be accurately and reliably placed on the substrate. It can be surface mounted.

According to the second and third aspects of the present invention, the positional deviation is extremely unlikely to occur, and the pads to be supplied with the cream solder are separated from each other, so that a short circuit between the pads due to the solder bridge can be prevented. It can be avoided.

[Brief description of drawings]

FIG. 1 shows a QFP according to a first embodiment of the present invention.
FIG. 3 is a partial schematic plan view showing a printed wiring board before being surface-mounted.

FIG. 2 is a partial schematic perspective view showing a printed wiring board and a metal mask before formation of a solder precoat layer.

FIG. 3 is also a partial schematic cross-sectional view showing a state in which a solder precoat layer is formed on a pad.

FIG. 4 is also a partial schematic perspective view showing a printed wiring board and a metal mask before cream solder printing.

FIG. 5 is also a partial schematic cross-sectional view showing a state in which cream solder is printed on the outermost pad.

FIG. 6 is a partial schematic cross-sectional view showing a state in which the bond flux is supplied onto the pad on which the solder precoat layer is formed.

FIG. 7 is likewise a partial schematic cross-sectional view showing a state where a chip component and QFP are mounted.

FIG. 8 is also a partial schematic cross-sectional view showing a state after collective reflow soldering.

FIG. 9 is a partial schematic perspective view showing that a paste for forming a solder precoat layer is being supplied in Example 2.

FIG. 10 is a partial schematic perspective view showing that cream solder is being supplied onto the outermost pads.

FIG. 11 is likewise a partial schematic cross-sectional view showing a state in which a chip part and a QFP are mounted.

FIG. 12 is also a partial schematic cross-sectional view showing a state after collective reflow soldering.

FIG. 13 is a partial schematic cross-sectional view showing a QFP on which a solder precoat layer is formed and a printed wiring board on which cream solder is supplied on a pad in Example 3.

FIG. 14 is also a partial schematic cross-sectional view showing a state after collective reflow soldering.

15 (a) to 15 (c) are partial schematic plan views for explaining a method of supplying cream solder in other examples 1 to 3. FIG.

16 (a) and 16 (b) are partial schematic plan views showing the shapes of the pads in other examples 4 and 5. FIG.

[Explanation of symbols]

1 ... QFP as a narrow pitch component, 2a, 2b ... Lead as an external connection terminal, 3, 20 ... Printed wiring board as a substrate, 4 ... Pad row, 4a, 24 ... (Specific) pad, 4b, 25, 27 ... Pads (other than specific pads), 8 ... Solder precoat layer as solder, 9 ... Cream solder, 15 ... Bond flux as flux adhesive.

Claims (3)

[Claims] 1. A method for surface-mounting a narrow-pitch component on a substrate having a pad array for mounting a narrow-pitch component via solder, wherein a specific pad among the pads forming the pad array is provided, And at least one of the external connection terminals of the narrow pitch component corresponding to the specific pad is covered with solder, cream solder is supplied onto pads other than the specific pad, and the specific pad and the external connection terminal In a state in which the flux adhesive is supplied onto at least one of the above, the external connection terminals of the narrow-pitch component are positioned and temporarily fixed on each pad, and then the cream solder and the solder that melts the solder are heated. Surface mounting method for pitch components. 2. The surface mounting method for a narrow pitch component according to claim 1, wherein the cream solder is supplied onto at least two pads which are not adjacent to each other. 3. The pad row is a pad row for surface-mounting a narrow pitch component having leads on all four side surfaces, and the cream solder is the outermost one of the pads constituting each pad row. 3. The surface mounting method for a narrow pitch component according to claim 2, wherein the surface mounting method is performed on the pad located at.