JPH10270837A - Cream solder printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cream solder printing method by which the required amount of cream solder for large-sized parts can be secured even when a thin solder mask is used. SOLUTION: After solder amount controlling projections 8, 9, 10 are provided around larger land copper foil 2 for which larger amounts of solder are required and solder masks are put on substrates 1A, 1B, and 1C, cream solder is printed on the substrates 1A, 1B, and 1C. Since the heights (h) of the projections 8, 9, and 10 increase the effective mask thicknesses to the land copper foil 2, the amount of solder supplied to the copper foil 2 is increased even when the solder masks themselves have such thin thicknesses that are suitable for smaller copper foil 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a cream solder printing method.

[0002]

2. Description of the Related Art When components are mounted on a printed circuit board (hereinafter, simply referred to as a board), cream solder is printed (or painted) on the board in advance using a solder mask.

(First Prior Art) A first prior art of the cream solder printing method will be described with reference to FIGS. 7A and 7B.

In a substrate 100 illustrated in FIG. 7A, a resist 7 is formed on an insulating plate 4 except for land conductor foils 2 and 3 which need to be soldered (generally, copper foils, hereinafter referred to as land copper foils). It has been applied. In the solder mask 200 corresponding to the substrate 100, through holes 22 and 23 that open corresponding to the land copper foils 2 and 3 are formed. The positions, shapes and sizes of these through holes 2 and 3 correspond to those of the land copper foils 2 and 3.

[0005] Such a solder mask 200 is applied to the substrate 100.
Then, the cream solder 40 is placed on the solder mask 200, and the squeegee 41 moves in the arrow direction 42 while pressing the squeegee 41 against the cream solder 40. Thereafter, when the solder mask 200 is removed as shown in FIG. 7B, the cream solder 40 is printed on the land copper foils 2 and 3. The amount of the printed cream solder 40 (solder amount) is generally given by the product of the opening areas of the through holes 22 and 23 and the mask thickness t.

In this case, if the mask thickness t is large, FIG.
As shown in (B), a part of the cream solder 40 remains on the inner peripheral surfaces of the through holes 22 and 23. Cream solder 40
Is smaller in the through hole 23 than in the large through hole 22. This is because the ratio of the inner peripheral area of the through hole to the area of the land copper foil increases as the mask thickness t increases and the area of the land copper foil decreases.
This is because the ratio of the adhesive force to the inner peripheral surface of the through hole becomes larger in the total adhesive force of the above. Therefore, it is difficult to control the amount of solder on the small land copper foil 3.

Therefore, considering the miniaturization of the land copper foil and the through hole due to the future miniaturization and high-density mounting of components,
We want to make the solder mask 200 thinner.

However, since the required amount of solder varies depending on the component, there is a problem that if the thickness of the solder mask 200 is reduced, the amount of solder is insufficient for a large component or the like.

(Second Prior Art) A second prior art of the cream solder printing method will be described with reference to FIGS.

A large land copper foil 2 and a small land copper foil 3 are formed on a substrate 110 illustrated in FIG. 13A. A resist 7 is formed on the insulating plate 4 except for the land copper foils 2 and 3.
Is applied, and characters or symbols (hereinafter, referred to as silk-printed portions) 15 are formed on the resist 7 by silk-screen printing. A large through hole 22 corresponding to the large land copper foil 2 and a small through hole 23 corresponding to the small land copper foil 3 are formed in the solder mask 210. However, as for the small through-hole 23, the amount of solder required for the small land copper foil 3 may be small, so that the recess 31 having a depth d is formed on the entire surface of the opening of the through-hole 23 only on the mask surface side by the half etching process. Are formed. The large through-hole 22 is the same as in the first prior art.

The presence of the recess 31 causes the solder mask 210
Even if the mask thickness t is large, the effective mask thickness t1 in the through hole 23 becomes thin as t−d. Therefore, the amount of cream solder remaining in the small through hole 23 is reduced, and the small land copper foil 3
A small amount of cream solder 40 can be printed thereon.

However, the surface of the substrate 110 is
And the thickness of the silk printing part 15 on it causes a step,
Not a perfect plane.

Therefore, the solder mask 210 is formed on the substrate 110.
When the squeegee is moved by superposing the squeegee, the solder mask 210 is deformed according to the unevenness due to the step.
As shown in (B), the cream solder 40 is printed, and stable and uniform printing cannot be performed. This will hinder future miniaturization and high-density mounting of components.

[0014]

SUMMARY OF THE INVENTION Accordingly, it is a first object of the present invention to provide a method capable of securing the amount of cream solder required for a large component even when the solder mask is thin.

Another object of the present invention is to provide a method capable of printing cream solder stably and uniformly without being affected by steps (unevenness) on the substrate surface.

[0016]

According to the first aspect of the present invention, there is provided a cream solder printing method which solves the first problem by controlling a solder amount on a substrate around a land conductor foil which requires an increase in the amount of cream solder. Wherein a solder mask is overlaid on the substrate and cream solder is printed thereon. Further, in the invention according to claim 2, the solder amount control projection is provided by silk printing. , Except for this projection,
The method is characterized in that silk printing is not performed on the substrate.

The cream solder printing method according to the third aspect of the present invention also solves the first problem. However, a solder mask is provided around a portion of a solder mask corresponding to a land conductor foil requiring an increased amount of cream solder. An amount control projection is provided, the solder mask is overlapped with the projection facing the substrate, and cream solder is printed. Further, in the invention according to claim 4,
Silk printing is not performed on the substrate.

Further, in the cream solder printing method according to the present invention, a plurality of the solder amount control projections are provided so as to be intermittently located around a land conductor foil requiring an increase in the amount of cream solder. It is characterized in that, in the cream solder printing method according to the invention of claim 6, each of the solder amount control projections, except for the connection pattern connected to the land conductor foil,
8. The cream solder printing method according to claim 7, wherein each of the protrusions for controlling the amount of cream solder is provided in a continuous shape substantially surrounding the entire circumference of the land conductor foil requiring an increase in the amount of cream solder. The land conductor foil is provided in a continuous shape completely surrounding the entire circumference of the land conductor foil which needs to be increased.

Next, a cream solder printing method according to an eighth aspect of the present invention solves the second problem, in which a concave portion for receiving a convex portion on the substrate side is provided on the back side of the mask around the opening of the through hole. And a solder amount control concave portion is formed on the mask surface side, and among the through holes in which the convex portion receiving concave portions are formed, the opening portions of the through holes corresponding to the land conductor foils that require a reduction in cream solder. It is characterized in that cream solder is printed on the land conductor foil on the substrate by using a solder mask formed around.

[0020]

According to the above construction, even if the solder mask itself is thin, the through-hole at the portion where the solder amount control projection exists is provided with the same projection even if the solder mask itself is thin. Is equivalent to an increase in the mask thickness by the height of. Since the mask thickness is effectively increased in this manner, the amount of cream solder also increases.

According to the second aspect of the present invention, the use of silk printing makes it possible to easily and easily provide the solder amount control projection. Also, if silk printing is not performed on the substrate except for the solder amount control projections, no extra step is formed on the substrate surface, and the height of the solder mask becomes uniform. Therefore, accurate control of the amount of solder can be easily and easily performed.

According to the fourth aspect of the present invention, since no silk-screen printing is performed on the substrate, no extra step is formed on the substrate surface, the height of the solder mask is made uniform, and accurate control of the amount of solder can be performed easily and easily. It can be done easily.

According to the fifth aspect of the present invention, a gap is formed between the solder amount control protrusions. However, there is no fear that the cream solder flows out of the gap unless the solder particles in the cream solder are made too small.

In the invention according to claim 6 or 7, since the solder amount control projections continuously or almost completely surround the entire circumference of the land conductor foil, there is no need to limit the size of the solder particles. In the invention according to claim 6, even when the connection pattern exists on the substrate surface, the solder amount control projection is interrupted at that portion, so that the height does not become uneven. The invention according to claim 7 is based on the assumption that there is no connection pattern on the substrate surface. In this case, the solder amount control projections may be completely continuous.

In the invention according to claim 8, the concave portion on the back surface side of the mask receives the convex portion such as resist or silk print on the substrate and absorbs the step on the substrate. Accordingly, deformation of the solder mask is reduced, and stable and uniform cream solder printing can be performed without being affected by steps. Further, even if the mask itself is thick, the concave portion on the mask surface side effectively reduces the mask thickness. Therefore, the amount of solder of the small land copper foil can be accurately controlled.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) A first embodiment of a cream solder printing method according to the present invention will be described with reference to FIGS. 1 to 3, in which a solder amount control projection is provided on the substrate side.

FIGS. 1 (A), 1 (B) and 1 (C) show the appearance of several examples of the substrate to be printed with cream solder in this embodiment. For simplicity, two types of large and small land copper foils 2 and 3 are made of insulating plates. 4, the large land copper foil 2 requires an increased amount of solder, and the small land copper foil 3 does not need to be increased. Each of the land copper foils 2, 3 is connected with connection patterns 5, 6, but a resist 7 is applied to substantially the entire surface of the substrate except for the land copper foils 2, 3. Note that the resist 7 may cover a part of the land copper foils 2 and 3 or may not cover at all. The connection pattern 5 of the large land copper foil 2 is formed on the front surface of the substrate in FIGS. 1A and 1B, but is formed on the back surface of the substrate in FIG. 1C.

In order to increase the amount of solder, the substrate 1A shown in FIG. 1A has solder amount control projections 8 on the resist 7 at the four corners around the large land copper foil 2. That is, 4
The individual projections 8 are provided intermittently.

In the substrate 1B shown in FIG. 1B, in order to increase the amount of solder, the amount of solder is controlled on the resist 7 in a continuous shape substantially surrounding the entire periphery of the large land copper foil 2 except for the connection pattern 5. A projection 9 is provided. The reason why the projection 9 is provided except for the connection pattern 5 is that
This is to prevent the mask height from becoming non-uniform due to the presence of the mask on the substrate surface.

In the substrate 1C shown in FIG. 1 (C), the connection pattern 5 connected to the large land copper foil 2 is on the back surface of the substrate and does not hinder the connection, so that the continuous pattern completely surrounds the entire circumference of the large land copper foil 2. A solder amount control projection 10 is provided on the resist 7 in a shape.

In each of the substrates 1A, 1B, and 1C, in this embodiment, the solder amount control projections 8, 9, and 10 are formed by silk printing. No projection is provided around the small land copper foil 3. Furthermore, except for the projections 8, 9 and 10, no silk printing of characters or symbols is performed on the resist 7. The height h of each of the projections 8, 9, 10 will be described later.

FIG. 2 shows a solder mask commonly corresponding to each of the substrates 1A to 1C shown in FIG. A large through hole 22 corresponding to the land copper foil 2 having a large position, shape and size and a small through hole 23 corresponding to the small land copper foil 3 are formed in the solder mask 21A. Solder mask 21A
Is made of stainless steel as an example, and has a thickness t1 that is sufficient to secure a necessary amount of solder for the small land copper foil 3.

Therefore, in this state, the solder mask 21A is too thin for the large land copper foil 2, so that the amount of solder is insufficient.

Therefore, the height h of the protrusions 8, 9, 10 for controlling the amount of solder provided on each of the substrates 1A, 1B, 1C is set to a height that allows the amount of cream solder to be increased by an amount required for the large land copper foil 2. .

Such a substrate 1A or 1B or 1C
When the solder mask 21A is overlapped with the solder mask 21A as shown in FIG.
+ H. When cream solder printing is performed in this state, as shown in FIG. 3B, the amount of the cream solder 40 attached to the through holes 22 and 23 decreases, and the large land copper foil 2 and the small land copper foil 3 Also, the cream solder 40 is printed in a necessary and sufficient amount for each.

In this embodiment, the solder amount controlling projections 8, 9,
Other than 10, no silk printing of characters or symbols is performed, because unevenness in height can be easily and easily avoided. Therefore, even if the characters or symbols are silk-printed, the projections 8 to 8 are avoided by avoiding these silk-printed portions.
10 can be provided, and when the height h of the projections 8 to 10 is higher than the silk-printed portion, no problem occurs.

The projections 8 to 10 may be provided by a method other than silk printing, and any material may be used as long as the material is an insulating substance.

(Second Embodiment) Next, referring to FIGS.
As a second embodiment of the cream solder printing method according to the present invention, a case where a solder amount control projection is provided on the solder mask side will be described.

First, with reference to FIGS. 5A and 5B, an example of a substrate to be printed with cream solder in this embodiment will be described.
5A and 5B, large and small types of land copper foils 2 and 3 are formed on the insulating plate 4 for simplicity. It is assumed that the large amount of solder needs to be increased in the large land copper foil 2, and the small land copper foil 3 does not need to increase the amount of solder. Each of the land copper foils 2, 3 is connected with connection patterns 5, 6, but a resist 7 is applied to substantially the entire surface of the substrate except for the land copper foils 2, 3. Silk printing of characters and symbols is not performed on the resist 7 at all. In addition, the resist 7 may cover a part of the land copper foils 2 and 3, or may not cover at all.

The connection pattern 5 for the large land copper foil 2 is formed on the front surface of the substrate 1D shown in FIG. 5A, but is formed on the back surface of the substrate 1E shown in FIG. 5B. ing.

Next, with reference to FIGS. 4A, 4B, and 4C, a description will be given of the solder mask corresponding to each of the above substrates. FIG.
5A and 5B show two types of solder masks corresponding to the substrate 1D of FIG. 5A viewed from the surface, and FIG.
The solder mask corresponding to the substrate 1E shown in FIG. Basically, a large through hole 22 corresponding to the land copper foil 2 having a large position, shape and size and a small through hole 23 corresponding to the small land copper foil 3 are formed.

Further, in order to increase the amount of solder, the solder mask 21B shown in FIG. 4A has solder amount control protrusions at four corners around the through hole 22 corresponding to the large land copper foil 2 on the back surface of the mask. 28 are provided. No projection is provided around the through hole 23 corresponding to the small land copper foil 3 and at the portions corresponding to the connection patterns 5 and 6.

In the solder mask 21C shown in FIG. 4B, a through hole 22 corresponding to the large land copper foil 2 is formed on the back surface of the mask except for a portion 25 corresponding to the connection pattern 5 in order to increase the amount of solder. Is provided in a continuous shape that substantially surrounds the entire circumference of. Small land copper foil 3
No protrusions are provided around the through hole 23 corresponding to the above and at the portion corresponding to the connection pattern 6 connected to the land copper foil 3.

In order to increase the amount of solder, the solder mask 21D shown in FIG. 4C has a continuous shape that completely surrounds the entire periphery of the through hole 22 corresponding to the large land copper foil 2 on the back surface of the mask. The projection 30 is provided. No protrusions are provided around the through hole 23 corresponding to the small land copper foil 3 and the portion corresponding to the connecting pattern 6 connected thereto.

In each of the above solder masks 21B, 21C and 21D, for example, it is made of stainless steel, and the thickness of the mask itself is thin enough to secure the amount of solder necessary for the small land copper foil 3, and is different from this. Projection 2 at body height h
8, 29 and 30 are made and joined with an adhesive or the like. The protrusion height h is a height at which cream solder can be increased by an amount required for the large land copper foil 2.

Such a substrate 1D and the solder mask 21B
(Or 21C), or when the substrate 1E and the solder mask 21D are overlapped, as shown in FIG. 6A, the effective mask thickness t2 increases to t1 + h in the large through hole 22. When cream solder printing is performed in this state, FIG.
As shown in the figure, the amount of the cream solder 40 attached to the through holes 22 and 23 is reduced, and the cream solder 40 is printed in a necessary and sufficient amount on both the large land copper foil 2 and the small land copper foil 3. .

Also in this embodiment, silk printing of characters and symbols is not performed on the substrates 1D and 1E at all, because unevenness in height can be easily and easily avoided.
Therefore, even if silk printing of characters and symbols is performed, the solder amount control projections 28 to
30 can be provided, and when the height h of the projections 28 to 30 is higher than the silk-printed portion, there is no problem.

The material for the solder amount control projections 28 to 30 may be any material, and may be a conductive material or an insulating material, and may be the same material as the solder masks 21B to 21D. For example, through holes 22 and 23 are formed in a stainless steel plate having a thickness of t1 + h, and a half-etching process is performed on the back surface of the stainless steel plate to a depth h to leave only the protruding portions 28 to 30, thereby producing solder masks 21B to 21D. .

Third Embodiment A third embodiment of the cream solder printing method according to the present invention will be described with reference to FIGS. 8 to 12, in which the influence of steps (unevenness) on a substrate is eliminated.

First, the substrate to be printed with cream solder in this embodiment will be described with reference to FIGS. FIG. 10 is a plan view of the substrate 1F, and FIG. 11 is a cross-sectional view taken along the line XI-XI. The substrate 1F has a large land copper foil 2 for large components and a small land copper foil 3 in two rows on the left and right for ICs (integrated circuits). A resist 7 is applied except for the land copper foils 2 and 3. ing. Further, on the resist 7, the part number (YYY) 1 near the large land copper foil 2
1 and a frame 12 indicating an IC installation site between rows of land copper foils 3
And the character 13 indicating the IC number (ICXX) in the vicinity
And a mark 14 indicating the 1st pin of the IC is drawn by silk printing. 4 is an insulating plate, 5 is a land copper foil 2
The connection pattern 6 indicates a land copper foil 3 connection pattern.

Next, an example of a solder mask corresponding to the substrate 1F will be described with reference to FIGS. FIG. 8 is a plan view of the solder mask 21E, and FIG. 9 is a cross-sectional view taken along the line IX-IX. In the solder mask 21E, a through hole 22 corresponding to the large land copper foil 2 and a through hole 23 corresponding to the small land copper foil 3 are formed. This solder mask 2
1E, on the front side, a recess 31 for controlling the amount of solder is formed all around the opening of the small through hole 23.

The thickness of the solder mask 21E itself is a thickness t for securing a necessary and sufficient amount of solder for the large land copper foil 2. Therefore, it is necessary to reduce the amount of solder for the small land copper foil 3 to a necessary and sufficient small amount. Therefore, the depth d of the solder amount control concave portion 31 is set so that the effective mask thickness in the small through hole 23 is small enough to secure this small amount of cream solder.

Further, a concave portion for receiving a convex portion on the substrate 1F is formed on the back surface side of the solder mask 21E. Among the convex receiving recesses, 32 is a resist receiving concave, 33 is a part number receiving concave, 34 is an IC installation frame receiving concave, 35 is an IC number receiving concave, and 36 is a 1st pin mark receiving concave. is there. These part number 11, IC
The installation frame 12, the IC number 13, and the first pin mark 14 are silk-printed portions. Therefore, the concave portions 33 to 36 are formed in the concave portion 32 for receiving the resist.

The depth of each of the convex receiving recesses 32 to 36 is the resist 7, the part number 11, the IC installation frame 12, and the IC number 13.
And the size of the first pin mark 14 is just set.

In this embodiment, the solder mask 21E is made of stainless steel, and the solder amount control recess 31, the resist receiving recess 32, the component number receiving recess 33, the IC installation frame receiving recess 34, and the IC number receiving recess 35. All of the first pin mark receiving concave portions 36 are formed by half etching.

When such a substrate 1F and the solder mask 21E are overlapped as shown in FIG.
And 11 to 14 all fit in the recesses 32 to 36. Therefore, without being affected by the step on the substrate, FIG.
The cream solder 40 can be printed stably and uniformly as shown in FIG. Also, in the small through hole 23, the mask thickness is effectively reduced by the solder amount control concave portion 31, so that
An appropriate amount of the cream solder 40 is printed on the small land copper foil 3.

In each of the first, second and third embodiments, the case where cream solder is printed on the printed circuit board has been described. However, the present invention is not limited to this. The present invention can be applied as a method of applying or printing on an arbitrary object.

[0059]

According to the first and third aspects of the present invention, even when the solder mask itself is thin, the mask thickness is effectively increased by the solder amount control projections on the substrate side or the solder mask side, and the desired thickness can be obtained. The amount of solder on the land copper foil can be increased.

According to the second aspect of the present invention, the solder amount control projection can be easily and easily provided on the substrate. In addition, since there is no silk-printed portion except for the solder amount control projection, accurate control of the solder amount can be performed easily and easily.

Also in the invention according to claim 4, since there is no silk-printed portion on the substrate, accurate control of the amount of solder can be performed easily and easily.

According to the fifth aspect of the present invention, the cream solder does not flow out of the gap between the solder amount control protrusions unless the solder particles in the cream solder are made too small.

According to the sixth or seventh aspect of the present invention, since the solder amount control projections continuously or substantially completely surround the entire circumference of the land conductor foil, there is no limitation on the size of the solder particles.

According to the invention of claim 8, since the concave portion on the back side of the mask receives the convex portion on the substrate and absorbs the step, stable and uniform cream solder printing can be performed. Further, even if the mask itself is thick, the mask thickness is effectively reduced by the concave portion on the mask surface side, and the amount of solder of the small land copper foil can be accurately controlled.

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of a substrate provided with a solder amount control projection as a first embodiment.

FIG. 2 is a plan view of a solder mask corresponding to each substrate of FIG. 1;

FIG. 3 is a sectional view showing a state of cream solder printing in the first embodiment.

FIG. 4 is a plan view of an example of a solder mask provided with a solder amount control projection as a second embodiment.

FIG. 5 is a plan view of an example of a substrate corresponding to each solder mask of FIG. 4;

FIG. 6 is a sectional view showing a state of cream solder printing in the second embodiment.

FIG. 7 is a sectional view showing a first conventional technique.

FIG. 8 is a plan view of a solder mask provided with a concave portion for controlling the amount of solder and a concave portion for receiving a convex portion as a third embodiment.

FIG. 9 is a sectional view taken along the line IX-IX in FIG. 8;

FIG. 10 is a plan view of an example of a substrate corresponding to the solder masks of FIGS. 8 and 9;

11 is a sectional view taken along the line XI-XI in FIG.

FIG. 12 is a sectional view showing a state of cream solder printing in the third embodiment.

FIG. 13 is a sectional view showing a second conventional technique.

[Explanation of symbols]

Reference Signs List 1A, 1B, 1C Substrate provided with solder amount control projection 1D, 1E substrate 1F Substrate having step (convex portion) 2 Large land copper foil 3 Small land copper foil 4 Insulating plate 5, 6 Connection pattern 7 Resist 8 , 9, 10 Projection for controlling solder amount on substrate side 11 Part number 12 IC mounting frame 13 IC number 14 1st pin mark 21A Solder mask 21B, 21C, 21D Solder mask provided with projection for controlling solder amount 21E Solder amount Solder mask provided with control concave portion and convex portion receiving concave portion 22 Large through hole 23 Small through hole 25, 26 Portion corresponding to connection pattern 28, 29, 30 Projecting portion for controlling solder amount on solder mask side 31 Solder amount Control recess 32 Resist receiving recess 33 Part number receiving recess 34 IC installation frame receiving recess 35 IC number receiving recess 36 First pinmer Receiving recess 40 cream solder 41 squeegee

Claims (8)

[Claims] 1. A method for providing solder amount control projections on a substrate around a land conductor foil requiring an increase in cream solder, overlaying a solder mask on the substrate from above the projections, and printing cream solder. Characteristic cream solder printing method. 2. The cream solder printing method according to claim 1, wherein the solder amount control projections are provided by silk printing, and silk printing is not performed on the substrate except for the projections. 3. A solder amount control projection is provided around a portion of the solder mask corresponding to the land conductor foil requiring an increase in cream solder, and the projection is directed toward the substrate, and the solder mask is overlaid. A cream solder printing method characterized by printing cream solder. 4. The cream solder printing method according to claim 3, wherein silk printing is not performed on the substrate. 5. A method according to claim 1, wherein a plurality of said solder amount control projections are provided so as to be intermittently located around a land conductor foil requiring an increase in cream solder.
The cream solder printing method according to any one of the above. 6. The solder amount control projection is provided in a continuous shape substantially surrounding the entire periphery of the land conductor foil requiring an increase in cream solder, except for a connection pattern connected to the land conductor foil. The cream solder printing method according to any one of claims 1 to 4. 7. The solder amount control projection according to claim 1, wherein the solder amount control projection is provided in a continuous shape completely surrounding the entire circumference of the land conductor foil requiring an increase in cream solder. Cream solder printing method. 8. A concave portion for receiving the convex portion on the substrate side is formed on the back surface of the mask around the opening of the through hole, and a concave portion for controlling the amount of solder is formed on the front surface side of the mask. Printing cream solder on the land conductor foil on the board using a solder mask formed around the opening of the through hole corresponding to the land conductor foil that requires a reduction in cream solder among the through holes formed. Characteristic cream solder printing method.