JPH0621634A - Flux application device to solder precoated wiring board - Google Patents

Abstract

PURPOSE:To obtain a fitted flux application state by providing a means for detecting unevenness of a flux application region and by controlling so as to increase a flux supply quantity at the time of detecting a projection part while reducing a flux supply quantity at the time of detecting a recessed part. CONSTITUTION:A cylinder 3 filled with a flux 1 is horizontally shifted by a ternary shifting mechanism in the direction to cross an arrangement part of the pads 27 in a state where a position in the vertical direction is fixed in contact with the surface of an insulated substrate 25 of a solder precoated wiring board 11. Then, when the contact 5 is located in a recessed part between the pads 27, a slight gap is opened between the contact 5 and the tip of the cylinder 1 so as to supply only a small quantity of flux 1. On the other hand, when the contact 5 is located on (projected part) the precoated solder 27, the contact 5 is pushed inside the cylinder 3 so as to increase a gap between the contact 5 and the cylinder 3 for supplying a large quantity of flux 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for applying a flux for soldering components to a printed wiring board whose pads are pre-coated with solder.

[0002]

2. Description of the Related Art In recent years, high-density surface mounting is becoming the mainstream for mounting electronic components on a printed wiring board in response to demands for smaller and lighter electronic devices and higher functionality. Among them, LSI
The number of packages is narrow, and the number of pitches is increasing.
QFP parts such as pins and 0.3 mm pitch are beginning to be put into practical use. In addition, a package form called TCP in which a semiconductor chip is joined to TAB and molded appears, and the lead pitch in this case is as fine as 0.1 to 0.3 mm.

Up to now, as a soldering method in surface mounting, there has been generally used a method in which cream solder is screen-printed on a pad of a wiring board, parts are placed on the pad, and heating is performed for soldering. However, as the pitch of the pads becomes narrower, the cream solder does not come off the screen, and the amount of solder supplied to the pads becomes too small.
Since the solder bridge and solder balls frequently occur due to the bleeding and sagging of the cream solder, the soldering yield is remarkably reduced.

If the pitch is about 0.3 mm, the yield cannot be improved by introducing a solder powder having a small particle diameter, a flux having little sagging, a highly accurate and smooth screen by the additive method, a highly accurate printing device and the like. However, these measures come at a huge cost.

Therefore, a technique has emerged that can stably solder components even at a narrow pitch. A typical example thereof is a solder precoat method in which a solder layer is formed on a pad before component mounting. The solder layer forming method includes a method of depositing solder only on the surface of the pad by a substitution reaction of an organic acid lead salt and tin powder, and a solder plating method which has been conventionally performed.

In order to mount a component by the solder precoating method, the component is temporarily fixed so as not to move when it is placed on a wiring board precoated with solder, and the oxide at the solder joint is reduced. It is then necessary to supply a flux that promotes solder wettability. Although it is possible to use an adhesive for temporary fixing of parts, it is possible to use a flux with high adhesiveness (temporary fixing flux) and temporarily fix the parts with flux, which saves man-hours. It is valid.

Conventionally, a screen printing method and a dispenser method have been known as methods for applying the flux to the pad region of the solder precoated wiring board. The screen printing method is the same as the method of applying cream solder, set the screen on the solder pre-coated wiring board, move the flux placed on it with a squeegee, and apply the flux only to the openings (pad array area). Is the way to do it. The dispenser method is a method in which a dispenser that pushes out flux is moved over the solder pre-coated wiring board and the flux is pushed out and applied only to the pad arrangement region.

[0008]

Since the solder precoat portion of the solder precoat wiring board protrudes from the surface of the insulating substrate by the thickness of the pad + the thickness of the precoat solder, the following problems occur. In other words, in the case of the screen printing method, the movement of the squeegee scrapes off the flux even if it is on the precoat solder, so there is almost no flux on the precoat solder and there is no gap between the pads. This results in the accumulation of excess flux.
For this reason, it is not possible to obtain a flux application state suitable for component mounting. Furthermore, the screen printing method cannot be applied to wiring boards on which other components have already been mounted. Also, in the case of wiring boards in which cream solder mounting and precoat solder mounting are mixed, cream solder and flux are applied before and after. Sometimes, it cannot be applied because the one applied first interferes with the one applied later.

Further, in the dispenser method, if the flux-coated surface has irregularities, the coating amount is likely to fluctuate, and the flux is only thin on the precoat solder that becomes the convex portions, and the flux is excessive between the pads that become the concave portions. The phenomenon that it accumulates easily occurs, and it is impossible to obtain a good flux coating state.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a flux coating device for a solder precoat wiring board which solves the above-mentioned problems, and its structure is such that the flux coating area of the solder precoat wiring board is contacted. While moving while detecting the unevenness of the flux application area, when this detecting means detects a convex part, the amount of flux supplied to that part is increased, and when a concave part is detected, the flux is supplied to that part. And a flux supply means for reducing the amount.

[0011]

In the flux application area of the solder pre-coated wiring board, there are a convex portion protruding from the surface of the insulating substrate by the thickness of the pad + the thickness of the pre-coated solder, and a concave portion therebetween.
The apparatus of the present invention detects this unevenness, increases the flux supply amount to that portion when a convex portion (precoat solder portion) is detected, and thickly coats the flux, and when a concave portion is detected, it applies to that portion. The amount of flux supplied is reduced so that the flux is applied as thinly as possible.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 and 2 show an embodiment of the present invention. This device comprises a cylinder 3 filled with flux 1. The lower portion of the cylinder 3 is tapered, and a spherical contactor 5 is rotatably held in the opening of the tip of the cylinder 3. Since the diameter of the tip opening of the cylinder 3 is slightly smaller than that of the spherical contactor 5, the spherical contactor 5 does not come out from the tip of the cylinder 3. The spherical contactor 5 is lightly pressed downward by the spring 7.
Therefore, in the state of FIG. 1, the tip end opening of the cylinder 3 is closed by the spherical contactor 5, and the flux 1 does not leak out. Reference numeral 9 is a guide tube for the spring 7.

As shown in FIG. 2, the cylinder 3 is supported by a three-dimensional moving mechanism 13 so that it can move in the X-axis, Y-axis, and Z-axis directions with respect to the solder precoat wiring board 11. A general-purpose mechanism such as a robot or an XY plotter system can be used as the three-dimensional movement mechanism 13, but the three-dimensional movement mechanism 13 shown in the figure is a substrate for horizontally supporting the solder pre-coated wiring board 11 in order to simplify the description. 15, a support column 17 movable in the direction perpendicular to the plane of the drawing (Y-axis direction) with respect to the base 15, a block 19 movable in the vertical direction (Z-axis direction) with respect to the support column 17, and a left and right with respect to the block 19. The arm 21 is movable in the direction (X-axis direction) and the holder 23 fixed to the tip of the arm 21.

Next, a flux applying method using this apparatus will be described with reference to FIGS. 3 and 4. In the figure,
Reference numeral 25 is an insulating substrate of the solder precoat wiring board 11, 27 is a pad, and 29 is precoat solder. Three-dimensional movement mechanism 1
3, the cylinder 3 is moved in a direction (arrow A direction) which crosses the array portion of the pads 27 while the vertical position is fixed such that the spherical contactor 5 makes light contact with the surface of the insulating substrate 25 of the solder precoat wiring board 11. ) To move horizontally.

Then, as shown in FIG. 3, when the spherical contactor 5 is in the concave portion between the pads 27, the spherical contactor 5 rotates while being slightly pushed into the cylinder 3, so that the spherical contactor 5 is rotated. And a slight gap is provided between the tip of the cylinder 3 and the flux 1 is slightly supplied from there. Further, as shown in FIG. 4, when the spherical contactor 5 is on the precoat solder 27 (convex portion), the spherical contactor 5 is equal to the thickness of the pad 27 + the thickness of the precoat solder 29 as compared with the case of FIG. Since it rotates while being pushed into the cylinder 3 only, the gap between the spherical contactor 5 and the tip of the cylinder 3 becomes large, and a larger amount of flux 1 than that in the case of FIG. 3 is supplied from there.

Therefore, according to this method, the flux 1 is applied thickly on the precoat solder 29 and the pad 2 is applied.
It is possible to obtain a preferable coating state when mounting a component in which the flux 1 is hardly coated in the concave portions between 7. In the apparatus of the above-mentioned embodiment, the spherical contactor 5 and the spring 7 act as unevenness detecting means, and the spherical contactor 5 and the cylinder 3 act as flux supplying means.

Next, another embodiment of the present invention will be described with reference to FIG. This apparatus is provided with an unevenness detector 33 and a flux supplier 35, which are arranged with a spacer 31 at a constant distance D. Although not shown, the unevenness detector 33 and the flux supplier 35 are moved in the direction of arrow A on the solder pre-coated wiring board 11 by the same three-dimensional movement mechanism as in the above embodiment.

The unevenness detector 33 has a pressure sensor 3 in the inner part of a bottomed cylindrical body 37 which houses the spherical contactor 5 and the spring 7.
9, the vertical displacement of the spherical contactor 5 caused by the unevenness of the surface of the solder precoat wiring board 11 is prevented by the spring 7
It is detected as a pressure change due to expansion and contraction of. Further, the flux supplier 35 supplies compressed air by opening and closing the valve 41 into the cylinder 3 filled with the flux 1.
The pressure causes the flux 1 to be pushed out from the nozzle 43 at the tip.

The pressure signal F detected by the pressure sensor 39 of the unevenness detector 33 is the pressure-which stores the relationship between pressure and displacement.
The displacement converter 45 converts the displacement signal ΔZ of the spherical contactor 5 into a delay circuit 47. The delay circuit 47 separately inputs the movement distance L of the unevenness detector 33 and the flux supplier 35 in the A direction, delays the displacement signal Δ by a time corresponding to the distance between the unevenness detector 33 and the flux supplier 35.
Output Z. This displacement signal ΔZ is calculated by
Displacement-valve opening degree converter 49 storing the relationship with the opening degree of
Is converted into a valve opening signal S, and the opening of the valve 41 is controlled by the signal S.

As a result, the flux supplier 35 discharges a predetermined amount of flux 1 from the nozzle 43 when the unevenness detector 33 reaches the position where the unevenness detector 33 detects the convex portion (precoat solder 29), and the unevenness detector 33 makes a concave portion. When the position (between the pads 27) is detected, the discharge of the flux 1 is stopped. Therefore, the flux 1 is applied thickly on the pre-coat solder 29, and the flux 1 is hardly applied to the concave portions between the pads 27, which makes it possible to obtain a flux applied state which is preferable for mounting components.

[0021]

As described above, according to the present invention, when the flux is applied to the solder pre-coated wiring board, the flux is applied thickly on the pre-coated solder and the flux is hardly applied to other portions. Since the state can be obtained, component mounting by precoat solder can be stably performed with high yield. Further, since the unevenness of the flux application area is detected by contact, there is no need for erroneous recognition and correction due to the reflection characteristics of the surface unlike the optical non-contact sensor, and the structure is simple and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of a flux coating device according to an embodiment of the present invention.

FIG. 2 is a front view showing the entire apparatus of FIG.

FIG. 3 is a cross-sectional view showing a usage state of the apparatus of FIG.

FIG. 4 is a sectional view showing a usage state of the apparatus of FIG.

FIG. 5 is a sectional view showing a main part of a flux coating device according to another embodiment of the present invention.

[Explanation of symbols]

 1: Flux 3: Cylinder 5: Spherical contactor 7: Spring 11: Solder pre-coated wiring board 13: Three-dimensional moving mechanism 25: Insulating substrate 27: Pad 29: Pre-coated solder 31: Spacer 33: Unevenness detector 35: Flux supply device 39: Pressure sensor 41: Valve

Claims (1)

[Claims] Claim: What is claimed is: 1. A means for moving a solder precoat wiring board while contacting a flux application area to detect irregularities in the flux application area, and a flux supply amount to that portion when the detection means detects a protrusion. And a flux supply means for reducing the amount of flux supplied to the concave portion when the concave portion is detected, and a flux applying apparatus for a solder pre-coated wiring board.