JP3279761B2 - Cream solder printing mask and printing method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask for printing cream solder in a reflow soldering process for manufacturing a PCB and a printing method using the mask.

[0002]

2. Description of the Related Art A cream solder printing mask is partially provided with a large-size printing mesh screen.
It is intended for cream solder printing masks used in the reflow soldering process of CB manufacturing and used for relatively small items such as chip electrodes and SOP / QFP / connector leads.

[0003] Most of these masks are currently manufactured by an etching method or an additive (electroforming) method. Etching masks on both sides of stainless steel or three-layer plate (copper or brass plate with nickel plating on both sides)
After the photosensitive resin is applied, it is exposed and developed through a film having a required opening shape, and the portion where the coating of the photosensitive resin is removed is opened with an etching solution (such as ferric chloride). . In this manufacturing method, since the metal is eroded from both sides, a convex portion is generated at the center of the inner wall of the opening.

The convex portion formed at the center of the inner wall of the opening becomes a catching portion and hinders the removal of the solder, so that the etching mask is not suitable for high quality printing. As the components used become finer in pitch, additive masks having better print quality than etching masks are increasingly used.

The additive method is also called an electroforming method, in which a female mold having an opening is formed of a photosensitive resin, and the periphery thereof is laminated by plating to form a mask plate. Since the shape of the photosensitive resin is relatively good and the shape can be transferred almost directly by plating, the shape of the opening is better than that of the etching mask. In either case, an optical process is required to form the opening pattern, and a chemical process is required to form the mask itself.

[0006] In the above-mentioned optical process, the production of a mask requires craftsmanship and is an important step that affects the print quality of the mask. An optically projected figure tends to deform a straight line portion into a round shape. For example, each side of a square is curved so as to bulge outward. Each corner lacks sharpness, and the tip (corner portion) assumes a round shape. In order to obtain the originally intended final shape, the film must be corrected in advance in a direction opposite to the tendency to be deformed, and it requires manual craftsmanship.

In the optical process, in addition to the above-mentioned processes, other important processes related to quality, such as pinhole inspection of a film or a photosensitive resin, misalignment of the front and back sides in a film bonding operation at the time of etching, etc. Supported by technology.

[0008] Also in the chemical process, there are many delicate parameters which affect the finish of the mask, and some of them are empirically controlled without knowing the mechanism. The mask has a large variation.

Further, a half-etching process is used as a processing method for a fine opening. The fine opening has a small target lead and a small amount of solder. Therefore, the thickness of the mask is reduced and the amount of solder is adjusted only around the fine portion. This is called half etching. Because this is a process for fine openings that are sensitive to quality,
As a base mask, an additive method having a higher quality than an etching method is often used.

However, in the half-etching process, the shape of the opening already formed is roughened by an etching solution or a subsequent correction process. In addition, since it is a fine portion that is easily affected by quality, various problems are easily caused. By the half-etching process, the amount of solder in the fine portion can be adjusted, and even if the opening width is small, the thinness of the mask can secure the releasability, but the printed solder quality is rather deteriorated.

As described above, according to the conventional manufacturing method, a metal material is processed by an etching method, an additive method, and a half-etching method. As a result, the mask quality is restricted as described above. .

In a mask based on such a conventional manufacturing method, a method for improving the shape of an opening is disclosed in
Japanese Unexamined Patent Application Publication No. Hei 4-94593 discloses a method for improving the smoothness and water repellency of the inner wall of an opening and improving the releasability of a cream solder. As a method for improving the manufacturing method of forming the opening, there is a mask using a laser drilling technique, but the above three proposals all use a metal mask as a material.

[0013]

The quality of the printed solder is greatly affected by the quality of the removability of the solder from the mask. Furthermore, the quality of the solder removability depends on the shape of the mask opening, the smoothness of the inner wall of the opening, and the water repellency. Conventionally, cream solder printing masks are formed with openings by applying a predetermined process to a metal mask. However, as described above, it is very difficult to form the inner wall of the opening smoothly. The quality of the opening affects the ease of removal of the solder, and thus the quality of the solder.

The present invention uses a plastic plate whose opening is formed by ablation using a laser having a short wavelength such as an excimer laser as a mask for printing cream solder, so that an opening having a predetermined shape can be accurately and finely formed. The present invention provides a cream solder printing mask having a configuration in which an opening has a property of excellent solder removability by improving the solder slip, and a printing method using the same. The purpose is to do so.

[0015]

According to the present invention, in order to achieve the above-mentioned object, the invention described in claim 1 is provided so as to correspond to a predetermined position of a printing object such as a printed wiring. A plastic plate having an opening formed therein, a printing frame to which the plastic plate is attached, and a cream solder printing mask separate from a printing object used for cream solder printing, comprising: The plate is made of a plastic material that can be processed by a short-wavelength laser such as an excimer laser; (b) the opening is formed by ablation using a short-wavelength laser such as an excimer laser; and (c) the planar shape of the opening. And the taper angle, by adjusting the energy density or the number of irradiation pulses of the laser,
It is set to adapt to the solderability of cream solder, and, (d) overlaying the plastic plate on the printing object, adhering cream solder to the predetermined position of the printing object through the opening, Subsequently, cream solder printing is performed by separating the plastic plate from the printing object, thereby providing a cream solder printing mask.

According to a second aspect of the present invention, the opening of the plastic plate is constituted by a fine pitch opening and a normal pitch opening, and the periphery of the periphery including the portion where the fine pitch opening is formed is provided. 2. The cream solder printing mask according to claim 1, wherein a step portion is formed thinner than a portion where the normal pitch opening is formed.

According to a third aspect of the present invention, the plastic plate is mixed with a substance such as a fine carbon powder capable of absorbing a short wavelength such as an excimer laser. The cream solder printing mask described in 1 above.

The invention according to claim 4 is the cream solder printing mask according to any one of claims 1 to 3, wherein the surface of the plastic plate is subjected to surface roughening.

According to a fifth aspect of the present invention, there is provided a printing method using the cream solder printing mask according to the first aspect, wherein a predetermined predetermined portion such as an opening of a plastic plate and a printed wiring of an object to be printed. In order to correspond to the position, the plastic plate is overlaid on the printing object, and while rubbing the cream solder with a squeegee, the cream solder that has passed through the opening of the plastic plate material is adhered to a predetermined position of the printing object, Thereafter, cream plastic printing is performed by separating the plastic plate from the printing object, and a printing method using a cream solder printing mask.

According to a sixth aspect of the present invention, in the printing method using the cream solder printing mask according to the second aspect, the fine pitch opening and the normal pitch opening of the plastic plate are respectively formed on the printed wiring board. While overlapping on the pad and rubbing the cream solder with a squeegee, the cream solder that has passed through the fine pitch opening and the normal pitch opening of the plastic plate material is respectively adhered onto the pad of the printed wiring board, and then the plastic A printing method using a cream solder printing mask, wherein cream solder printing is performed by separating a plate from the printing object.

According to a seventh aspect of the present invention, the plastic plate is mixed with a substance such as a fine carbon powder capable of absorbing a short wavelength such as an excimer laser. A printing method using the cream solder printing mask described in 1).

The invention according to claim 8 is a printing method using a cream solder printing mask according to any one of claims 5 to 7, wherein the surface of the plastic plate is roughened. Is the way.

[0023]

According to the present invention, (a) the plastic plate is made of a plastic material which can be processed with a short wavelength laser such as an excimer laser, and (b) the opening is formed by ablation using a short wavelength laser such as an excimer laser. Formed,
(C) The planar shape and the taper angle of the opening are adjusted by adjusting the energy density or the number of irradiation pulses of the laser.
It is set to adapt to the solderability of the cream solder, and (d) the plastic plate is overlaid on the printing object, and the cream solder is adhered to the predetermined position of the printing object through the opening, Subsequently, by separating the plastic plate from the object to be printed, cream solder printing can be performed, so that the opening that affects print quality due to the plastic plate that was considered unusable as a printing mask was removed. It can be processed finely and with high precision. For this reason, it is possible to provide the industry with a printing mask that can obtain high quality with inexpensive materials such as plastics, and to process plastic materials with a short wavelength laser such as an excimer laser. In this case, the inner wall shape of the opening is better than that of the conventional metal mask because it has a good lubrication Therefore, without using chemicals for optical processing and chemical processing as in the past, high-precision micro-pitch openings can be achieved by using a laser beam, which is an environmentally friendly means, while reducing processing costs. Part can be manufactured, and the opening can supply the cream solder which is originally required to the pad of the printed wiring board accurately through the inner wall with excellent cream solder releasability. This has the effect of enabling printing at a fine pitch.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a cream solder printing mask of the present invention. An aluminum square pipe printing frame 1 supports the outside of a polyester screen 2, and the polyester screen 2 has an adhesive portion inside. A plastic plate 4, which is a main part of the printing mask, is attached via 3.

An opening is formed in a plastic plate used as a printing mask by using ablation processing of a short wavelength laser such as an excimer laser. Specifically, the laser beam output from the excimer laser oscillator body passes through a light-shielding aperture mask of a predetermined shape,
By irradiating the plastic plate via the projection lens, an opening having a predetermined shape is formed.

At this time, as for the material of the plastic plate to be used, as for the easily ablated plastic such as polyimide, polyester, epoxy and polycarbonate, the opening can be processed as it is. For plastics such as polyethylene, polypropylene, polyacetal, and Teflon, which were difficult or impossible to process by ablation, materials that easily absorb the wavelength of the excimer laser, such as fine carbon powder, were used to promote ablation. By mixing, the opening can be processed.

For example, when a polyacetal resin plate, which has been difficult to process by ablation, is used as a printing mask, a fine carbon powder having a weight ratio of 5% is mixed into the material to promote ablation. Since the strength is high and the water repellency is good, a mask made of a plastic plate having good solder removability can be obtained.

The width (or diameter) of the laser beam passing through the light-shielding aperture mask for determining the processing shape, and the width (or diameter) of the irradiation beam focused on the surface of the plastic plate by the beam reducing projection lens Is the beam reduction ratio, and the reciprocal of the square of this reduction ratio is the energy density ratio. By adjusting the energy density or changing the number of irradiation pulses, the planar state of the opening and the taper angle can be set to desired values.

The relationship between the energy density and the taper angle is such that when the energy density is large, the taper angle is small, and when the energy density is small, the taper angle is large. When the energy density is gradually increased and reaches a certain value, the taper angle decreases, but a plastic plate mixed with a substance that absorbs the wavelength of the excimer laser such as carbon powder may cause cracks on the back side. .

As described above, if the taper angle of the opening of the printing mask formed in the resin which is hardly ablated and mixed with the carbon powder is too large, the solder removability is impaired. Therefore, particularly in the case of a plastic plate mixed with carbon powder or the like, the energy density needs to be smaller than the level at which cracks occur, and if it is set to such an extent that a necessary taper angle is obtained, a good opening is formed. can do.

When the energy density cannot be changed, the taper angle can be adjusted by changing the number of irradiation pulses. In addition, the pulse frequency is set to 20, 50, 200 Hz / 500 Hz / sec or less.
The change in the taper angle when the change was made to sec was examined. However, no change was observed in the difference in the taper angle due to the change in the pulse frequency. As described above, by controlling each of the resin thickness, the shape of the light-shielding aperture mask, and the laser irradiation parameters, it is possible to perform processing in which the hole thickness, the opening plane shape, the taper angle, and the like are freely changed. .

In FIG. 2, the squeegee 5 moves from one end to the other end of the plastic plate 4 while rubbing the cream solder 6 against the plastic plate 4 having the opening formed by the above-described means. It shows a state in which As shown in FIG. 3, a fine pitch opening 7a and a normal pitch opening 7b
The periphery including the portion where the fine pitch opening 7a is formed is thinner than the portion where the normal pitch opening 7b is formed, and the stepped portion 8 is formed. The portion 8 is useful for securing the solder detachability and suppressing the amount of solder.

FIG. 4 is an enlarged sectional view showing a part of the mask portion made of the plastic plate 4 including the stepped portion 8.
When a mask portion made of a plastic plate 4 is superimposed on a printed wiring board 10 and a cream solder 6 is rubbed with a squeegee 5, a fine pitch opening 7a and a normal pitch opening 7 are formed.
b, the cream solder 6 is printed on the pads 11 of the printed wiring board 10, respectively. When the mask portion made of the plastic board 4 rises and separates from the printed wiring board 10, the cream solder 6 is printed on the printed wiring board 10. Are fine pitch cream solder 9a and normal pitch cream solder 9b
Are printed respectively.

FIG. 5 shows that when the conventional metal mask 12 is used, a projection 13a is formed at the center position of the inner wall of the opening 13, a projection 13b is formed at the back end of the inner wall, or the surface of the inner wall is formed. The case where the notch 13c is formed at the end is shown. As a result, the cream solder supplied on the pads 11 of the printed wiring board 10 becomes insufficient as shown at 14, or short-circuited as at 15, or an unfavorable state occurs. In the case of the plastic plate of the present invention, Such a disadvantage is solved.

The mask portion made of the plastic plate of the present invention has a property that its surface has a good slip. Therefore, with the movement of the squeegee, the cream solder moves on the plastic plate without slipping and loses the rolling property. Is not pushed into the opening. As described above, in the case of a material having a good surface slip, the surface of the plastic plate 4 is formed as shown in FIG.
A rough surface can be formed by surface roughening (rough surface processing) 17 as shown in FIG. In the figure, reference numeral 16 denotes fine carbon powder.

In the present invention, in particular, when a plastic plate which is difficult to ablate is used, since fine carbon powder is mixed in the plastic plate, no static electricity is generated and the electronic device may be damaged by the static electricity. Has no advantages.

In FIG. 7, as means for attaching the plastic plate 4 of the present invention to the printing frame 1, different from FIG. 1, both sides of the plastic plate 4 are attached to holding brackets 18a and 18b.
The tension springs 19a, 19b are arranged between the printing frame 1 and the holding fittings 18a, 18b. Usually, the holding fittings 18a, 18b are operated by the action of the tension springs 19a, 19b.
b are positioning brackets 20a, 20 provided on the printing frame 1.
b.

[0038]

According to the present invention, the plastic plate, which is considered to be unusable as a printing mask, can finely and precisely process the opening which affects the printing quality, and thus can be used in industry. The effect of providing a printing mask that can obtain high quality with inexpensive material called plastic, the inner wall shape of the opening compared to the conventional metal mask when processing plastic material with short wavelength laser such as excimer laser Then, it has good smoothness adapted to the solder paste removal properties, and reduces the processing cost by means of laser beam-free environmental pollution without using conventional chemicals for optical and chemical processes. However, it is possible to produce high-definition fine-pitch openings, and the openings are excellent in cream solder removability. Interior wall it is possible to accurately supply the cream solder that originally required on the printed wiring board pads via, for which has the effect, that enables the printing of a fine pitch.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of an entire mask on which a plastic plate is attached as a printing mask.

FIG. 2 is a cross-sectional view showing a state where cream solder is printed using the mask of FIG. 1;

FIG. 3 is an enlarged plan view showing a part of a mask in which an opening is formed.

FIG. 4 is an enlarged cross-sectional view showing a fine pitch opening, a normal pitch opening, and a state of cream solder printed on a printed wiring board when the plastic plate of the present invention is used.

FIG. 5 is an enlarged sectional view showing an example of a printing state using a conventional metal mask for comparison with FIG.

FIG. 6 is a partial cross-sectional view showing a state where the surface of a plastic plate is roughened.

FIG. 7 is an overall schematic plan view of another embodiment showing means different from FIG. 1 when a plastic plate is attached as a printing mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Print frame 2 Screen 3 Adhesion part 4 Plastic board 5 Squeegee 6 Cream solder 10 Printed wiring board 11 Pad

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-113069 (JP, A) JP-A-3-72364 (JP, A) JP-A-5-112083 (JP, A) JP-A-4- 327993 (JP, A) JP-A-5-185269 (JP, A) JP-A-5-229091 (JP, A) JP-A-60-107342 (JP, A) JP-A-5-35339 (JP, U) Actual opening 4-122065 (JP, U)

Claims (8)

(57) [Claims] 1. An object to be printed such as a printed wiring is determined in advance.
With openings formed to correspond to the specified positions
A plastic plate and a mark to which the plastic plate is attached
Printing frame and printing used for cream solder printing consisting of
In a cream solder printing mask separate from the object, ( a ) the plastic plate has a short wavelength such as an excimer laser.
Laser is made workable plastic material, (ii) a laser the opening of the short wavelength of an excimer laser or the like
It is formed by ablation processing by, (c) the planar shape and the taper angle of the opening, the laser
By adjusting the energy density or the number of irradiation pulses,
It is set to adapt to the removability of cream solder.
Ri and superimposed the plastic plate to the printing object (D), wherein
Apply cream solder through the opening to the location on the object
The plastic plate is then adhered in place,
Separated from the print object, cream solder printing
Cream solder printing machine
Sk. 2. The method according to claim 1, wherein the opening of the plastic plate is fine.
It consists of a pitch opening and a normal pitch opening.
To include the portion where the fine pitch opening is formed.
Around the area where the normal pitch opening is formed.
It is characterized by the formation of a terraced section that is thinner
The cream solder printing mask according to claim 1. 3. An excimer glass on the plastic plate.
Materials such as fine carbon powder that can absorb short wavelengths such as
Are mixed with each other.
The cream solder printing mask on the list. 4. The surface of the plastic plate is roughened.
The method according to any one of claims 1 to 3, wherein the processing is performed.
The cream solder printing mask described in the above. 5. The cream solder printing machine according to claim 1, wherein
In printing how using disk, printed circuit or the like of the printing object opening in the plastic plate
So as to correspond to a predetermined position of
Lay the plastic plate on the printing object, and rub the cream solder with a squeegee.
Printing the cream solder that passed through the opening of the tick board
Attach it to a predetermined position on the object, and then separate the plastic plate from the object to be printed
By solder paste mark, characterized by a cream solder printing
A printing method using a printing mask. 6. The cream solder printing machine according to claim 2, wherein
In the printing method using a disc, the fine pitch opening of the plastic plate and the normal pitch opening
Lay the mouth on the pads of the printed wiring board and rub the cream solder with a squeegee.
Fine pitch and normal pitch openings in tic plate
And the cream solder passed through each of the printed wiring
Deposited on the pads of the substrate and then separating the plastic plate from the printing object
By solder paste mark, characterized by a cream solder printing
A printing method using a printing mask. 7. An excimer glass on the plastic plate.
Materials such as fine carbon powder that can absorb short wavelengths such as
Is mixed. 7. The method according to claim 5, wherein
Printing method using the cream solder printing mask described above. 8. The surface of the plastic plate is roughened.
8. The method according to claim 5, wherein the processing is performed.
A printing method using the cream solder printing mask described in the above.