JP2009006578A - Squeegee structure for cream solder printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a squeegee for cream solder printing which can hardly swell due to a cream solder, even in case a rubber material with high follow-up properties is used. <P>SOLUTION: This squeezee 10 is equipped with a holder 13, a urethane rubber 11 of an elastic member, fitted to the holder 13 and a stainless plate 12, of higher rigidity than the urethane rubber 11, superposed on the urethane rubber 11. In this squeeze 10 which prints the cream solder 20 on a substrate 25 by the tip of the urethane rubber 11, the stainless plate 12 is shorter than the urethane rubber 11, and the urethane rubber 11 is retained by the holder 13, tilting in the proceeding direction F. In addition, the stainless plate 12 is superposed on the side, in the proceeding direction F, of the urethane rubber 11 and a first exposure area 11a where the urethane rubber 11 and the stainless plate 12 are exposed but not superposed over each other, is formed on the substrate 25 side of the urethane rubber 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a technique for reducing the influence of swelling of a squeegee for cream solder printing used for printing cream solder on a substrate.

As a technique for printing cream solder on a substrate, a method in which a mask is placed on a substrate and the solder paste is spread using a squeegee while the mask is placed thereon has been adopted.
Since such a squeegee requires solution resistance and wear resistance, a metal squeegee or a rubber squeegee using urethane rubber or the like is used.
A metal squeegee is used when the smoothness of the printing surface is high. This is because the squeegee is made of metal, so there is little deflection, and solution resistance and wear resistance can be obtained.
On the other hand, rubber-based squeegees are used when the smoothness of the printing surface is low and the squeegee is required to follow.

In Patent Document 1, by attaching an elastic body such as polyurethane rubber to the surface of a rigid body such as a metal plate, the elasticity of the abutting portion to the printing surface is secured by the elastic body, and the bending rigidity of the squeegee is increased. A technique for securing with a rigid body is disclosed.
Patent Document 2 discloses a technique for securing elasticity and bending rigidity by stacking a metal plate on a rubber plate and sandwiching it between holders.

In Patent Document 3, a rubber plate is embedded in a metal plate as a core material, and the flexibility that can follow the convex surface of the printing surface by using it as a squeegee and the hardness that does not bend even when a sufficient squeegee pressure is applied. Techniques to ensure are disclosed.
In Patent Document 4, a metal thin plate is projected on the printing surface side of a squeegee made of polyurethane rubber and sandwiched between stack holders, and the protruding portion of the metal thin plate is used as a squeegee by contacting the surface to be printed. A technique for preventing the occurrence is disclosed.
Patent Document 5 discloses that a squeegee is formed by sandwiching urethane rubber between a bent first metal plate and a second metal plate in a holder to form a squeegee even when the viscosity of ink such as cream solder is high. Techniques that can prevent this are disclosed.

JP 2003-127356 A JP 10-86327 A Noto 3039978 Japanese Utility Model Publication No. 7-11338 JP-A-8-118598

However, the conventional techniques disclosed in Patent Documents 1 to 5 are considered to have the following problems.
(A) Problems when using a metal-based squeegee When using a metal-based squeegee in which a metal member is brought into contact with the printing surface, the squeegee's deflection is reduced, but the ability to follow the printing surface is sacrificed.
Considering both the solder joint reliability and the defect rate at the time of soldering, there is a need to change the thickness of the solder paste for each part on the same substrate. For this reason, a step is provided on the screen placed on the substrate.
If a metal squeegee is used for a screen having such a step, the squeegee does not follow the step of the screen, so that the thickness of the solder paste on the same substrate cannot be changed for each part.

(B) Problems when using rubber-based squeegees In recent years, lead-free cream solder has been used in consideration of environmental problems. For this reason, in order to obtain the printability of solder, the holding property until the solder is melt-cured, and the property of removing the oxide at the soldering site, the aggressiveness of the solvent used in the cream solder to the squeegee is increasing.
The urethane rubber used in the squeegee swells and deforms due to the solvent used in the cream solder, and the straightness of the tip of the squeegee cannot be maintained. As a result, printing blur and printing unevenness are generated.

  Accordingly, an object of the present invention is to provide a cream solder printing squeegee structure that is difficult to swell by cream solder even when a rubber-based material having high followability is used.

In order to achieve the above object, the cream solder printing squeegee structure according to the present invention has the following characteristics.
(1) A holder, a squeegee main body made of an elastic member attached to the holder, and a first hard plate that is stiffer than the squeegee main body superimposed on the squeegee main body, and cream solder at the tip of the squeegee main body In the squeegee structure for cream solder printing that prints on the substrate,
The first hard plate is shorter than the squeegee main body, the squeegee main body is tilted in the moving direction and held by the holder, and the first hard plate is overlapped with the moving direction side surface of the squeegee main body, A first exposed surface is formed on the substrate side of the squeegee body so that the squeegee body and the first hard plate are exposed without overlapping.

(2) In the squeegee structure for cream solder printing according to (1),
A tapered surface having an obtuse angle with respect to the first exposed surface is formed at a tip of the first hard plate on the substrate side.

(3) In the squeegee structure for cream solder printing according to (1) or (2),
A second hard plate shorter than the squeegee main body is provided so as to sandwich the squeegee main body with the first hard plate, and the squeegee main body and the second hard plate are disposed on the substrate side of the squeegee main body. A second exposed surface that is exposed without overlapping is formed.

(4) In the squeegee structure for cream solder printing according to any one of (1) to (3),
The angle formed by the tapered surface of the first hard plate and the first exposed surface is 120 degrees.

With the cream solder printing squeegee structure according to the present invention having such characteristics, the following actions and effects can be obtained.
First, the invention described in (1) includes a holder, a squeegee main body made of an elastic member attached to the holder, and a first hard plate that is stiffer than the squeegee main body superimposed on the squeegee main body. In the cream solder printing squeegee structure in which cream solder is printed on the substrate at the tip of the first squeegee, the first hard plate is shorter in length than the squeegee body, and the squeegee body is tilted in the advancing direction and held by the holder. The first hard plate is stacked on the side surface in the traveling direction of the squeegee body, and a first exposed surface is formed on the substrate side of the squeegee main body so that the squeegee main body and the first hard plate are exposed without overlapping.

By superimposing the first hard plate on the side surface in the traveling direction of the squeegee body, it is possible to minimize the portion where the cream solder contacts. Thereby, even if a rubber squeegee is employed, deformation due to swelling, collapse of the surface, and the like can be suppressed.
Moreover, the followability by the elastic force of an elastic member is not impaired by providing the 1st exposed surface in which a 1st hard board does not overlap in a board | substrate side.
Therefore, it is possible to provide a cream solder printing squeegee structure that is difficult to swell with cream solder even when a rubber-based material having high followability is used.

In the invention described in (2), the cream solder printing squeegee structure described in (1) is a taper that forms an obtuse angle with respect to the first exposed surface at the tip of the first hard plate on the substrate side. Since the surface is formed, the rolling of the cream solder is not hindered.
In order to supply a predetermined amount of solder to fine holes provided in a metal mask placed on a substrate, the rolling property of cream solder is important. The cream solder moves forward while rolling the side surface in the direction of travel of the squeegee body, so that the cream solder enters the fine holes provided in the metal mask, and the necessary amount of cream solder is printed at the required position. Become. When the rolling property is deteriorated, the cream solder becomes difficult to enter the hole of the metal mask, and printing unevenness and printing blur occur.
However, by providing a tapered surface on the first hard plate stacked on the traveling direction side of the squeegee body, it is possible to prevent printing unevenness and printing blurring without inhibiting the rolling property of the cream solder.

The applicant has confirmed through experiments that it is desirable that the taper surface having an obtuse angle with respect to the squeegee body and the first exposed surface be about 120 degrees as described in (4).
Basically, if the tapered surface is formed on the first hard plate, the rolling property of the cream solder is not hindered. However, in order to achieve both the securing of the bending rigidity of the first hard plate and the surface that does not impair the rolling property, it is desirable to set it to about 120 degrees.

  The invention described in (3) is shorter in length than the squeegee body so that the squeegee body is sandwiched between one hard plate in the cream solder printing squeegee structure described in (1) or (2). Since the 2nd hard board is provided and the 2nd exposure surface in which the squeegee body and the 2nd hard board are exposed without overlapping is formed in the substrate side of the squeegee body, the 2nd exposure surface which hits the back side of the 1st exposure surface Thus, it is possible to improve the holding performance by sandwiching the squeegee body between the first hard plate and the second hard plate without hindering the followability of the squeegee body.

  The squeegee body should avoid the portion other than the first exposed surface coming into contact with the cream solder as much as possible. Therefore, the 1st hard board has covered the advancing direction side of the squeegee main body, leaving the 1st exposed surface. Furthermore, the second hard plate is also provided on the opposite surface, and the squeegee main body is sandwiched so that the cream solder is less likely to enter the surface between the squeegee main body and the first hard plate. As a result, cream solder is less likely to adhere to the surface of the squeegee body other than the first exposed surface, and a squeegee structure capable of suppressing deformation due to swelling of the squeegee body and surface collapse can be provided.

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, the configuration of the first embodiment will be described.
In FIG. 1, the perspective view of the squeegee 10 of 1st Embodiment is shown. FIG. 2 is a sectional view of the squeegee 10.
The squeegee 10 is configured by sandwiching a urethane rubber 11 and a stainless steel plate 12 between holders 13.
The urethane rubber 11 is a plate material corresponding to the squeegee body, having a thickness of about 20 mm to 30 mm, and a urethane hardness of about 60 to 70. The squeegee body is not limited to polyurethane, but various materials such as fluorine rubber, butyl rubber, neoprene rubber, and silicone rubber can be considered, but any material that can provide chemical resistance to the cream solder 20 can be used. I do not care. However, it is necessary to appropriately select the thickness and hardness so that an appropriate elasticity can be obtained depending on the material to be selected.

The stainless steel plate 12 has a thickness of about 1 mm, and a tapered surface 12a is provided at the tip on the substrate 25 side. Since the material may be a metal having corrosion resistance, it is not limited to stainless steel, and for example, an iron plate coated with an ultra high polymer such as PTFE, a titanium plate, or the like may be used. A material that is not corroded by the cream solder 20 and has bending rigidity is preferable. Therefore, a resin material may be used.
The stainless steel plate 12 is overlapped so that the first exposed surface 11 a is formed on the traveling direction side of the urethane rubber 11. The width of the first exposed surface 11a may be about 5 mm. However, it is not hindered to change appropriately depending on the balance between the elasticity of the urethane rubber 11 and the bending rigidity of the stainless steel plate 12.

Urethane rubber 11 and stainless steel plate 12 are stacked and held by holder 13 at the top. In the first embodiment, the bolt 14 is used to fasten the urethane rubber 11 and the stainless steel plate 12 together. As for the fixing method, any method may be adopted as long as the urethane rubber 11 and the stainless steel plate 12 can be held by the holder 13 so as not to fall.
The holder 13 is attached to the robot arm 16 and moves horizontally on the metal mask 30 provided on the substrate 25.
The metal mask 30 is a plate provided with a print pattern as shown in FIG. 1, and is fixed in a state where tension is applied by a frame 31.

The metal mask 30 is preferably subjected to construction that improves the peelability of cream solder, such as coating a stainless steel with an ultra high polymer such as PTFE.
After the metal mask 30 is overlaid on the substrate 25 and positioned, the cream solder 20 is printed by the squeegee 10 so that a predetermined amount of the cream solder 20 is applied to a predetermined position.
As shown in FIG. 2, the metal mask 30 is provided with two types of deep holes 32 and stepped holes 33. Some chips soldered to the substrate 25 have a narrow solder pitch and can easily form a bridge. Therefore, in order to reduce the amount of solder and make it difficult for bridging to occur, the invention is devised so that printing can be performed with a small amount of solder using the stepped holes 33.
The cream solder 20 is a general one having good rolling properties.

Since the structure of the squeegee 10 of the first embodiment is the configuration described above, the following operation is exhibited.
A squeegee 10 provided on a production line (not shown) superimposes a metal mask 30 set on a frame 31 on a substrate 25 placed on a conveyor (not shown).
Then, after the cream solder 20 is spread in a row on the metal mask 30, screen printing is performed by the squeegee 10.
FIG. 3 is an enlarged cross-sectional view showing how the cream solder 20 is inserted into the deep hole 32 by the squeegee 10. FIG. 4 is a cross-sectional view showing a state in which the cream solder 20 is inserted into the deep hole 32 and the stepped hole 33 by the squeegee 10.
First, an appropriate amount of cream solder 20 is applied to the end of the metal mask 30. This operation (not shown) may be performed manually or automatically using a syringe or the like.

Then, the squeegee 10 is lowered to the end of the metal mask 30 so that the tip of the urethane rubber 11 contacts the metal mask 30. As shown in FIG. 3, the urethane rubber 11 is given a pressing force P by the robot arm 16 so as to be pressed against the metal mask 30 downward in the drawing, that is, on the substrate 25 side. Therefore, the contact portion of the urethane rubber 11 with the metal mask 30 is slightly bent.
Then, the squeegee 10 is slid in the traveling direction F while maintaining the pressing force P.
When the urethane rubber 11 of the squeegee 10 is advanced from the state of FIG. 2 in the traveling direction F, the cream solder 20 is inserted into the deep hole 32 and the stepped hole 33 of the metal mask 30, and the cream solder is placed at a predetermined position on the substrate 25. 20 is printed in a predetermined amount.

The cream solder 20 rolls on the metal mask 30 and advances in the traveling direction F while contacting the first exposed surface 11a of the urethane rubber 11 and the stainless steel plate 12.
The exposed length a, which is the difference between the urethane rubber 11 and the stainless steel plate 12, is about 5 mm, and the angle θ formed by the tapered surface 12a and the first exposed surface 11a is about 120 degrees. The cream solder 20 rolls on the metal mask 30 while rotating in the rolling direction R while contacting the first exposed surface 11a and the tapered surface 12a.
When the cream solder 20 reaches the portion where the deep hole 32 as shown in FIG. 3 is formed, the cream solder 20 enters the deep hole 32 while rolling.
After the urethane rubber 11 passes, the cream solder 20 remains in the deep hole 32 as shown in FIG.

  Further, since the pressing force P is applied to the urethane rubber 11 when it reaches the stepped hole 33, the step of the metal mask 30 is performed at the stepped hole 33 portion along the counterbore portion 33a as shown in FIG. Deforms following the surface shape. The height of the counterbore part 33a is about 30 to 80 μm, and the urethane rubber 11 follows sufficiently. By doing so, the cream solder 20 is inserted into the lower hole 33b, and the cream solder 20 is printed on the substrate 25 by the height of the lower hole 33b.

Since the structure of the squeegee 10 of the first embodiment has the configuration and operation described above, the following effects can be obtained.
The first effect is that deformation due to swelling of the urethane rubber 11 and surface collapse are kept to a minimum.
In the first embodiment, a holder 13, a urethane rubber 11 made of an elastic member attached to the holder 13, and a stainless steel plate 12 that is stiffer than the urethane rubber 11 stacked on the urethane rubber 11 are provided. In the squeegee 10 for printing the cream solder 20 on the substrate 25 at the tip, the stainless steel plate 12 is shorter in length than the urethane rubber 11, and the urethane rubber 11 is held in the holder 13 while being inclined in the traveling direction F. The plate 12 is overlapped on the side surface F of the urethane rubber 11 in the traveling direction F, and a first exposed surface 11a is formed on the urethane rubber 11 on the substrate 25 side so that the urethane rubber 11 and the stainless steel plate 12 are exposed without overlapping.

Therefore, by overlapping the stainless steel plate 12 on the side surface of the urethane rubber 11 in the traveling direction F, the portion where the cream solder 20 contacts is minimized. In other words, the portion where the urethane rubber 11 contacts the cream solder 20 is only the first exposed surface 11a, and the contact portion can be minimized, so even if a rubber squeegee is used for screen printing of the cream solder 20. Further, deformation due to swelling of the urethane rubber 11 and surface collapse can be suppressed.
Moreover, the followability by the elastic force of the urethane rubber 11 is not impaired by providing the first exposed surface 11a on the substrate 25 side where the stainless steel plate 12 does not overlap.
As far as the applicant confirms, the area in which the elastic force of the urethane rubber 11 contributes to the ability to follow the unevenness of the metal mask 30 is not so wide.

In the structure of the squeegee 10 of the first embodiment, by providing the first exposed surface 11a at the tip of about 5 mm, the stepped hole 33 of the metal mask 30 is sufficiently tracked, and the necessary amount of cream solder 20 is placed in the lower hole 33b. It is confirmed that can be applied. Therefore, if only a necessary part is exposed, the followability of the urethane rubber 11 to the metal mask 30 can be ensured.
Thus, by extending the stainless steel plate 12 in the traveling direction F of the urethane rubber 11 and exposing only the first exposed surface 11a, it is possible to extend the life of the urethane rubber 11. Although it depends on the frequency of use of the squeegee 10, it is inevitable that the urethane rubber 11 deteriorates as long as it contacts the cream solder 20. However, by replacing the stainless plate 12 and minimizing the first exposed surface 11a, the replacement frequency of the urethane rubber 11 could be halved.

Moreover, the point which does not impair the rolling property of the cream solder 20 by the taper surface 12a provided in the stainless steel plate 12 as a 2nd effect is mentioned.
Since the tapered surface 12a having an obtuse angle with respect to the first exposed surface 11a is formed at the tip of the stainless steel plate 12 on the substrate 25 side, rolling of the cream solder 20 is not hindered.
In order to supply a predetermined amount of solder to the lower hole 33b provided in the metal mask 30 placed on the substrate 25, the rolling property of the cream solder 20 is important. The cream solder 20 moves forward while rolling the side surface of the urethane rubber 11 in the direction of travel F, so that the cream solder 20 enters a minute hole provided in the metal mask 30 and the necessary amount of cream solder 20 is placed at a required position. Will be printed. When the rolling property is deteriorated, it becomes difficult for the cream solder 20 to enter the hole of the metal mask 30, and printing unevenness and printing blurring occur.

However, by providing the tapered surface 12a on the stainless steel plate 12 stacked on the traveling direction F side of the urethane rubber 11, the rolling property of the cream solder 20 is not hindered and printing unevenness and printing blur can be prevented.
In the first embodiment, a satisfactory result was obtained by setting the angle θ to 120 degrees. However, since the plate thickness of the stainless steel plate 12 is thin, the influence of the angle θ is not so great. Therefore, if this angle is an obtuse angle, it will be 100 degrees or 150 degrees.
In view of emphasizing the rolling property of the cream solder 20, it is desirable to make the angle as obtuse as possible. However, if the angle θ of the tapered surface 12a is increased too much, there is a concern that the bending rigidity of the stainless steel plate 12 may be lowered. is important.
In addition to this, it is considered that R-surface processing such as curling on the urethane rubber 11 side may be performed instead of simply forming the tapered surface 12a.

[Second Embodiment]
Next, the configuration of the second embodiment will be described.
In FIG. 5, sectional drawing of the squeegee 10 of 2nd Embodiment is shown.
The structure of the squeegee 10 of the second embodiment is substantially the same as the structure of the squeegee 10 of the first embodiment. However, the urethane rubber 11 is superposed not only on the stainless steel plate 12 but also on the back plate 15 and is sandwiched between the holders 13.
The back plate 15 may be made of any material as long as it has an appropriate rigidity, but a stainless plate having a thickness of about 1 mm is used using the same material as the stainless plate 12. This is because the back plate 15 desirably has high corrosion resistance in terms of handling the cream solder 20.
The urethane rubber 11 is sandwiched between the stainless plate 12 and the back plate 15 and is held by the holder 13.

Since 2nd Embodiment is said structure, there exists an effect as described below.
FIG. 6 shows an enlarged cross-sectional view of the tip of the squeegee 10.
In the printing of the cream solder 20 using the squeegee 10, when the depth of the counterbore part 33a of the stepped hole 33 is deep, there is a case where it is desired to increase the pressing force P in order to improve the followability of the urethane rubber 11. There is also a desire to increase the sliding speed in the traveling direction F in order to increase productivity.
In this way, when the pressing force P is increased or the speed in the traveling direction F is increased, the urethane rubber 11 may bend more than necessary as shown in FIG. When it bends like the urethane rubber 11 shown by the broken line, a gap C is formed between the stainless steel plate 12 and the urethane rubber 11.

When the gap C is generated, the cream solder 20 enters the gap C while rolling. As a result, the urethane rubber 11 may be deformed. If the urethane rubber 11 is deformed, printing blur and printing unevenness occur, which is not preferable.
Moreover, since the contact area of the urethane rubber 11 and the cream solder 20 becomes wide, there is a problem that the life of the urethane rubber 11 is reduced.
Such a problem can be avoided if the urethane rubber 11 and the stainless steel plate 12 are bonded. However, since the urethane rubber 11 and the stainless steel plate 12 are separated at the time of replacement, only the urethane rubber 11 is replaced. The rubber 11 and the stainless steel plate 12 should not be bonded.

This is because the replacement cycle of the urethane rubber 11 is about once a month, and therefore there is a demand for ensuring the ease of replacement and a demand for reducing the cost of replacement parts as much as possible.
Therefore, the back plate 15 is provided on the back surface of the urethane rubber 11 to prevent the gap C from being generated, thereby preventing the cream solder 20 from entering the gap C.
The reason why the second exposed surface 11b is provided when the back plate 15 and the urethane rubber 11 are overlapped is to prevent the followability of the urethane rubber 11 from being hindered.
The second exposed surface 11b is set to have the same distance as the first exposed surface 11a, that is, the same exposure length a.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above-described examples, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, the materials shown in the first embodiment and the second embodiment are not particularly limited, and may be appropriately changed as necessary. Further, these shapes can be appropriately changed without departing from the scope of the invention.

The perspective view of the squeegee 10 of 1st Embodiment of this invention is shown. 1 is a sectional view of a squeegee 10 according to a first embodiment of the present invention. The expanded sectional view showing a mode that the cream solder 20 is inserted in the deep hole 32 by the squeegee 10 of 1st Embodiment of this invention is shown. Sectional drawing showing a mode that the cream solder 20 was inserted in the deep hole 32 and the stepped hole 33 with the squeegee 10 of 1st Embodiment of this invention is shown. Sectional drawing of the squeegee 10 of 2nd Embodiment of this invention is shown. The expanded sectional view showing a mode that the cream solder 20 is inserted in the deep hole 32 by the squeegee 10 of 2nd Embodiment of this invention is shown.

Explanation of symbols

10 Squeegee 11 Urethane rubber 11a First exposed surface 11b Second exposed surface 12 Stainless steel plate 12a Tapered surface 13 Holder 14 Bolt 15 Back plate 16 Robot arm 20 Cream solder 25 Substrate 30 Metal mask 31 Frame 32 Deep hole 33 Stepped hole 33a Counterbore Portion 33b Lower hole θ Angle C Clearance F Traveling direction P Pressing force R Rolling direction a Exposure length

Claims (3)

A holder, a squeegee body made of an elastic member attached to the holder, and a first hard plate that is stiffer than the squeegee body overlaid on the squeegee body, and the cream solder is placed on the substrate at the tip of the squeegee body In squeegee structure for cream solder printing to print on
The first hard plate is shorter than the squeegee body,
The squeegee body is held in a holder inclined in the traveling direction,
The first hard plate is stacked on a side surface in the traveling direction of the squeegee body, and a first exposed surface is formed on the substrate side of the squeegee body so that the squeegee body and the first hard plate are exposed without overlapping. A squeegee structure for cream solder printing. In the squeegee structure for cream solder printing according to claim 1,
A squeegee structure for cream solder printing, wherein a taper surface having an obtuse angle with respect to the first exposed surface is formed at a tip of the first hard plate on the substrate side. In the squeegee structure for cream solder printing according to claim 1 or 2,
A second hard plate having a shorter length than the squeegee main body so as to sandwich the squeegee main body with the first hard plate;
A squeegee structure for cream solder printing, wherein a second exposed surface is formed on the substrate side of the squeegee body so that the squeegee body and the second hard plate are exposed without overlapping.

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