TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cream solder printing squeegee and a cream solder printing method used when mixedly mounting different kinds of electronic components on a circuit board.
When a heterogeneous electronic component, for example, a semiconductor bare chip and other electronic components are mixedly mounted on a circuit board, as shown in FIG. 7, first, a primary mounting step of mounting the semiconductor chip 1 on the circuit board 2 in a face-down state. After that, the metal mask 3 on which the convex portion 3a covering the mounted semiconductor chip 1 is formed is overlaid on the circuit board 2, and the cream solder 4 for other electronic components is screened on the land 2a. It is printed (for example, see Patent Document 1).
[Patent Document 1]
[Problems to be solved by the invention]
However, when the metal mask 3 as described above is used, the cream solder is precisely and simultaneously attached to the circuit forming land 2a through the opening 3b adjacent to the convex portion 3a and the opening (not shown) remote from the convex portion 3a. Is difficult to print. That is, when printing a generally-used substantially flat squeegee up and down along the protruding portion 3a, depending on the squeegee riding on the protruding portion 3a, the opening 3b adjacent to the protruding portion 3a may be removed. Excessive cream solder cannot be scraped off, and it is necessary to separately scrape the cream solder between the opening 3b adjacent to the convex portion 3a and the other opening. This not only complicates the operation of the squeegee, but also causes variations in the amount of cream solder printed.
An object of the present invention is to provide a cream solder printing squeegee and a cream solder printing method capable of uniformly and accurately controlling a cream solder printing amount.
[Means for Solving the Problems]
In order to solve the above-mentioned problem, an invention according to claim 1 is to overlay a metal mask having a convex portion on a circuit board and screen-print cream solder supplied on the metal mask on the circuit board. Wherein a plurality of cut portions are formed at a tip end portion which is in close contact with the metal mask, and each cut portion is independently deformable at each boundary. According to this, when the squeegee is moved in the direction along the flat portion of the metal mask, the squeegee can be in close contact with the flat portion without deformation, while the convex portion is convex with the cut portion as a boundary. The squeegee can be overcome by a deformed portion of the squeegee which is freely deformed part by part along the convex portion, and the cream solder can be printed through an opening adjacent to the convex portion as well as through an opening remote from the convex portion. Therefore, the cream solder can be printed uniformly and with high accuracy regardless of whether or not the area is near the convex portion.
According to a second aspect of the present invention, in the cream solder printing squeegee, the cut portions are formed at equal intervals in the longitudinal direction of the squeegee, and since the cut portions are present at equal intervals, a force is uniformly applied on the metal mask. Since it is added, cream solder can be printed more uniformly and with high precision.
According to a third aspect of the present invention, in the above-described squeegee for cream solder printing, the cut portion is formed in a direction oblique to the longitudinal direction of the squeegee, and particularly, the tip of the squeegee formed of a material having high hardness such as urethane rubber. Part deformability can be improved.
The invention according to claim 4 is a method in which a plurality of sheets are arranged in parallel along the moving direction. Even if the first squeegee gets over the convex portion, the second squeegee may be removed even if it scrapes off the excess cream solder near the convex portion. Squeegee (and the subsequent squeegee) will scrape off, and cream solder can be printed more uniformly and with higher precision.
According to a fifth aspect of the present invention, a metal mask on which a convex portion covering the electronic component is formed is superimposed on the circuit board on which the electronic component is mounted, and the cream solder supplied on the metal mask is placed on the circuit board. When screen printing is performed, a squeegee having a plurality of cut portions formed at the tip is moved along the flat portion of the metal mask to print cream solder, and the convex portion of the metal mask is formed by cutting the cut portion. The squeegee, which is partially deformed as a boundary, gets over the deformed portion, so that cream solder can be printed uniformly and with high accuracy regardless of whether it is in the vicinity of the convex portion or not.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIGS. 1A and 1B are a perspective view and a bottom view, respectively, showing a configuration of a squeegee according to a first embodiment of the present invention.
The squeegee 5 is formed in a substantially flat plate-like shape using a resilient material such as urethane rubber in the same manner as a conventional squeegee, and is reduced in thickness like a sword tip so that one side along the longitudinal direction is easily adhered to a printing object. I have. Therefore, it can be mounted on a conventional cream solder printing machine with the other side along the longitudinal direction as the base end.
The squeegee 5 differs from the conventional squeegee in that a plurality of slits 6 cut in the direction toward the base end are arranged along the longitudinal direction of the squeegee 5 at the tip of the sword. The cutting depth of the slit 6 and the slit interval are set so as to be independently deformable one by one with each slit 6 as a boundary. For example, in a urethane rubber squeegee 5 having a maximum width of 10 mm and a length of 200 mm in the V-shaped cross section of the tip of the sword, the slits 6 are machined so as to be 1 mm at equal intervals and 5 mm in depth.
Hereinafter, a cream solder printing method using the above-described squeegee when a heterogeneous electronic component is mixedly mounted on a circuit board will be described.
First, as shown in FIG. 2, a primary mounting step of mounting the semiconductor chip 1 on the circuit board 2 in a face-down state (flip chip mounting) is performed, and thereafter, a convex portion ( The metal mask 3 on which the embossed portion 3a is formed is overlaid on the circuit board 2.
Then, the squeegee 5 mounted on the cream solder printing machine (not shown) is moved so that the tip is in the horizontal direction (the direction in which the flat part of the metal mask is arranged) and the entire tip is the metal mask 3. Adjust so that a load is evenly applied to the flat part. At this time, there is no need to install and adjust the squeegee 5 so that the slit 6 is along the edge of the convex portion 3a of the metal mask 3.
Next, as shown in the cross-sectional view of FIG. 3A, the cream solder 4 is discharged onto the metal mask 3 and the squeegee 5 is moved in a predetermined direction along the horizontal direction. As a result, the tip of the squeegee 5 moves in close contact with the flat portion of the metal mask 3, and the cream solder 4 is filled in the opening 3 b opened in the flat portion, while the opening 3 b opens. Also, the excess cream solder 4 is scraped off and printed on the land 2a.
When the squeegee 5 reaches the convex portion 3a, a part of the squeegee 5 has a convex portion with each slit 6 as a boundary, as shown in a transverse sectional view of FIG. 3B and a vertical sectional view of FIG. While the squeegee 5 moves over the convex portion 3a while freely deforming along the convex portion 3a, the remaining portion of the squeegee 5 moves in close contact with the flat portion on the side of the convex portion 3a, and the squeegee 5 moves into the opening 3b opened to the flat portion. The excess cream solder 4 above the opening 3b is scraped off while the cream solder 4 is being filled, and the cream solder 4 is printed on the land 2a. At this time, since the slits 6 are present at equal intervals, a force is uniformly applied to the metal mask 3.
As a result, as shown in the cross-sectional view of FIG. 4A and the vertical cross-sectional view of FIG. 4B, the opening 3a adjacent to the convex portion 3a also has the opening 3b separated from the convex portion 3a. Similarly, the cream solder 4 is uniformly filled, and the excess cream solder 4 does not remain on the opening 3a. In other words, the cream solder 4 having the same volume as each opening volume can be printed on the predetermined land 2a of the circuit board 2 through each opening 3a.
Although illustration is omitted, after the printing is completed, the electronic component and the surface-mounted component are mounted on the printed portion of the cream solder 4 and the cream solder 4 is melted in a reflow process to electrically connect the electronic component and the surface-mounted component. A circuit is formed by fixing the connection.
In this manner, the cream solder 4 can be easily and accurately printed using the metal mask 3 having the protruding portions 3a, and a high-quality heterogeneous electronic component mixed-mounted circuit board can be manufactured.
FIG. 5 is a (a) front view and (b) a bottom view of the squeegee according to the second embodiment of the present invention.
The squeegee 5 differs from that of the first embodiment in that the slit 8 is formed obliquely to the longitudinal direction of the squeegee.
Thereby, the deformability of the tip of the squeegee 5 made of urethane rubber having a particularly high hardness can be improved. The angle α when the slits 7 are formed in the oblique direction is determined by the slit interval d and the dimension a of the slits 7 in the thickness direction of the squeegee 5, so that adjacent slits do not overlap and independent deformation is not hindered. And tan α ≧ a / (d / 2).
FIG. 6 is a side view of the squeegee according to the third embodiment of the present invention.
A plurality of first squeegees 5A and second squeegees 5B are arranged in parallel along the moving direction. Each of the squeegees 5A and 5B is of any of the first and second embodiments described above.
As a result, even if the first squeegee 5A passes over the convex portion 3a and the cream solder 4 around the first squeegee 5A is scraped off, the second squeegee 5B will scrape off the solder. The cream solder 4 can be printed.
In each of the above-described embodiments, the shape of the squeegee 5 has been described as having a sword-shaped tip. However, the shape is not limited to this. For example, a squeegee having another shape, such as a flat plate having no sword-shaped tip. It is clear that similar effects can be obtained by forming slits in the same manner.
Further, although the material of the squeegee 5 has been described as urethane rubber, it is apparent that the same effect can be obtained even if the squeegee 5 is made of a resin material other than urethane.
The above-described cream solder printing method can be applied to various circuit boards such as a flexible film.
【The invention's effect】
As described above, according to the present invention, a plurality of cuts are formed at the tip of the squeegee, and the cuts are partially deformable independently of each other at the boundaries, so that a semiconductor chip or the like is mounted. It is possible to easily and accurately perform cream solder printing by overlaying a metal mask on which a convex portion covering a semiconductor chip etc. is formed on a circuit board. It became possible to manufacture.
[Brief description of the drawings]
FIG. 2 is a configuration diagram of a squeegee according to the first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a state where the squeegee of FIG. 1 is installed on a circuit board.
FIG. 4 is a sectional view showing a state in which cream solder is printed on a circuit board by moving the squeegee of FIG. 2;
FIG. 5 is a sectional view showing the state of the circuit board after the printing process using the squeegee of FIG. 3 is completed.
FIG. 6 is a configuration diagram of a squeegee according to a second embodiment of the present invention.
FIG. 7 is a configuration diagram of a squeegee according to a third embodiment of the present invention.
Cross-sectional view of a conventional circuit board on which heterogeneous electronic components are mounted using a cream solder printing method with a squeegee.
2 circuit board 2a land 3 metal mask 3a convex portion 3b opening 4 cream solder 5 squeegee 6 slit (cut portion)
7 slits (cuts)