JPH06152108A - Coating method for printed wiring board and printed wiring board - Google Patents

Abstract

PURPOSE:To form a very thick film of solder resist, etc., on a printed wiring board easily with an excellent controllability without increasing the cost and to control and conduct easily the filling and opening of a through hole and the opening of a component insertion hole at the time of coating of the thin film. CONSTITUTION:First, a curtain 5 of liquid coating material is formed. A printed wiring board 1 is moved, crossing the curtain, to apply coating material on the surface of the board uniformly. At a wiring margin around a mini via- through hole 2, a cutout (slit) is preliminarily formed. During the movement of the printed wiring board through the curtain, the coating material is caused to flow into the through hole, breaking the equilibrium of the surface tension of the coating material, and then a selective filling of the mini via-through hole with coating material is conducted at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a printed wiring board and a printed wiring board, and more particularly to a coating layer (insulating layer, overcoat layer) on the front and back surfaces of a relatively inexpensive double-sided printed wiring board. The present invention relates to a technique for forming a film with a film thickness.

[0002]

2. Description of the Related Art With the increasing demand for high-density packaging, the production of double-sided, multi-layer boards having through-holes has shown significant growth. The mainstream of double-sided and multi-layer boards is resin-based boards, which have the features of low cost, high-density mounting, easy upsizing of the board, and good electromagnetic shielding.

Both sides using glass / epoxy resin substrate,
Taking a multilayer printed wiring board as an example, the typical manufacturing process is to form a through hole in a copper-clad laminate, plating the through hole and the front and back surfaces, protecting the through hole, curing, drawing a circuit pattern, and a surface. The process includes the steps of forming a wiring pattern by etching the backside copper foil, protecting it, forming an insulating layer, protecting it, patterning the insulating layer by etching, and forming a component mark.

The protection / insulation layer not only plays a role of ensuring electrical insulation between the electronic components to be subsequently mounted and wiring, and also protects against foreign matters due to overcoating of the substrate, and also has reliability due to an electromagnetic shielding function and the like. Therefore, the formation of the protective and insulating layers is important for manufacturing a high-quality mounting board in response to customer needs.

There are various techniques for forming protective and insulating layers.
As a relatively inexpensive one, a coating technique of a solder resist (hereinafter referred to as a solder resist) by spraying or a dipping forming technique is often used.

Further, as a relatively expensive one, a contact type forming technique such as screen printing of a polymer thick film (that is, a coating material is applied while a jig such as a squeegee or a roller is brought into contact with a printed wiring board). Method).

[0007]

When the solder resist layer is formed by spray coating or dipping, the maximum film thickness that can be formed is limited to about 15 to 16 μm.

That is, spray coating is inefficient because of the property of spraying a liquid, and it is impossible to set a high film thickness. Further, it is difficult to control the film thickness with high precision, and there are other problems such as uneconomical and air pollution.

Since the dip immerses the substrate in the liquid resist, the liquid flows down the substrate and the high film thickness cannot be set. In addition, there is a problem that the liquid flows down to the lower side due to gravity and the lower side of the substrate becomes thicker than the upper side of the substrate to cause nonuniformity, and the controllability of the thickness is not good.

Further, as described above, the protection and the high film thickness of the insulating layer cannot be set by a relatively inexpensive method.
In the process of soldering electronic circuit parts to the board, a highly penetrable water-soluble flux (flux that can be washed with water) cannot be used, and a paste is used.
In this case, there is also a problem that dechlorocarbonization cannot be achieved because the fluorocarbon cleaning is required.

Further, in reality, there is a demand for mounting a circuit that handles a high voltage of several tens of volts or more on a double-sided mounting board,
There is a demand to improve the noise (radiated noise) shielding property. In this case, it is indispensable to set a high film thickness for the insulating and protective films. Therefore, even if the cost increases, for example,
There is no choice but to cope with this by forming the polymer thick film by screen printing multiple times.

In this case, in addition to the high cost, the process is complicated due to the contact of the roller and the squeegee with the substrate, and the skill of the operator is required for uniform coating. There is.

The present invention has been made in view of the above circumstances. Therefore, one of the objects of the present invention is to easily and controllably improve the cost of a solder resist while suppressing the cost increase. It is to be able to form a film thickness.

Furthermore, there is another important problem that the present inventor has paid attention to when manufacturing a double-sided printed wiring board. That is, it is a problem of handling the insulating and protective films in the through hole (bias through hole) and the component insertion hole.

Holes (openings) used in printed wiring boards
Type is a part insertion hole (mainly for inserting parts and soldering on the back side, the diameter is 1.0 mm ~
1.1 mm), semi-through hole (also a part is inserted, but the circuit to be connected is only on one side, the diameter is 1.0 mm to 1.1 mm), mini bias through hole (on the front and back sides) It is a hole used only for energizing and connecting circuits and has a diameter of 0.3 mm to 0.6 mm).

Regarding the component insertion hole and the half through hole,
The holes must not be closed to ensure the insertion of parts. For this reason, when insulating with a solder resist or forming a protective film, protection by a mask (tenting, etc.), curing, or subsequent etching etc. Steps such as opening the hole are required.

Regarding the mini-bias lure holes only for energization, some customers require the products to be left open, and in order to prevent the accumulation of solder residue or solder balls in the mini-bias lures holes. In some cases, in order to prevent the residual of chemicals such as plating solution, the mini bias through hole is required to be filled and delivered, and when different and troublesome processes are required for each customer. There is also.

The present invention has been made paying attention to such a point, and therefore, another object of the present invention is to easily and controllably solder resist while suppressing the above-mentioned cost increase. When enabling the formation of high film thickness such as
At the same time, it is possible to easily control and execute the filling and opening of the mini bias through hole, and the opening of the component insertion hole and the half through hole.

[0019]

The outline of a typical one of the present invention is as follows. (1) In the present invention, a liquid coating material is flowed down over a predetermined width and under a flow rate control to form a waterfall of the coating material, and the printed board is moved over the waterfall at a predetermined speed. It is characterized in that the coating material is instantaneously passed through so that the coating material falling from above is applied substantially evenly on the printed wiring board to coat the printed wiring board.

As a desirable mode, the printed board is moved substantially horizontally, and the waterfall flow of the coating material is set so as to drop substantially perpendicular to the coating surface of the printed board.

(2) Further, the coating material has a viscosity such that the action of the surface tension is not impaired, and the surface tension is utilized to apply the coating material to at least the component insertion hole of the double-sided printed circuit board. It is characterized by preventing intrusion.

(3) When it is required to fill the mini bias through hole (through hole used only for energization), the wiring margin portion around the through hole is provided with a through hole from the outer periphery of the margin portion. A notch (slit) that reaches the hole is provided, and this notch causes an imbalance in the surface tension of the coating material, allowing the coating material to flow into the through hole, thereby filling the mini bias through hole. .

(4) Further, it is characterized in that a solder resist is used as a coating material to realize a high film thickness setting of 20 μm or more. (5) Further, the present invention is a double-sided printed wiring board in which a circuit pattern is formed on the front and back surfaces and a part of the circuit pattern on the front and back surfaces is electrically connected through a through hole. The wiring margins around the through holes on the front and back surfaces of the wiring board are provided with notches (slits) reaching the through holes from the outer periphery of the margin portions. The printed wiring board is characterized by being filled with a coating material that covers a circuit pattern on the back surface.

[0024]

[Action]

(1) Consider a model as shown in FIG. In this case, the double-sided printed wiring board 1 is moving at the speed V in the horizontal direction. Liquid solder resist waterfall (curtain) 5
It is designed to fall almost perpendicularly to the substrate at a flow rate of Scm ³ / sec. The thickness of the solder resist waterfall is ΔX as shown in the lower part of FIG.

At this time, the time t required for the portion of the lateral width ΔX of the substrate 1 to pass through the waterfall of the solder resist is t.
= ΔX / V, and the solder resist amount falling on the substrate during that time is S · t = S · (ΔX / V)
Is. Therefore, the flow rate of solder resist Scm ³ /
By changing sec or the moving speed V of the substrate, the amount of resist applied on the substrate per unit time can be accurately changed. That is, it is possible to set an arbitrary film thickness (for example, 20 μm to 150 μm).

Next, since the solder resist falls over the entire width of the substrate 1 in a substantially vertical direction, uneven coating in the lateral direction of the substrate does not occur. In addition, the substrate 1 has a speed V
Since the waterfall of the solder resist is cut through at a substantially right angle, the solder resist dropped on the coating surface of the substrate 1 is uniformly stretched in the vertical direction (rearward) of the substrate by the inertial force. Therefore, a uniform solder resist film having an arbitrary film thickness (for example, 20 μm to 150 μm) can be formed with good controllability.

(2) When the solder resist film is formed by the above-mentioned method, it is feared that the liquid solder resist may penetrate into the component insertion hole or the through hole to block the hole. As a result of observation, it was found that such a situation can be automatically avoided.

That is, taking the mini bias through hole as an example, when the solder resist 21 covers the through hole 2 as shown in FIG. 3A, the surface tension is caused by the surface tension as shown in FIG. 3B. An even pulling force is generated, which ruptures the solder resist and automatically secures the opening of the through hole. The same applies to the component insertion hole and the half through hole. This eliminates the need to remove the solder resist filled in the component insertion holes after forming the insulating and protective layers.

(3) However, depending on the customer, in order to prevent the accumulation of solder residue or solder balls in the mini bias through hole used only for energization, or to prevent the chemical such as plating solution from remaining. In some cases, you may be required to fill in the mini bias lurehole and deliver it.

In this case, as shown in FIG. 11A, a slit 71 is formed in the wiring margin (wiring allowance portion in consideration of the positional deviation between the hole and the wiring) 20.
In this state, when the solder resist is applied by the above-mentioned method, as shown in FIG. 11B, the presence of the slits causes the surface tension to be unbalanced and the solder resist flows into the through holes 2. As a result, the mini bias through hole can be automatically filled. Therefore, an independent hole filling step is unnecessary.

[0031]

Embodiments of the present invention will now be described with reference to the drawings. (Embodiment 1) FIG. 1 is a plan view for explaining a typical aspect of a method for coating a printed wiring board according to the present invention.

On the coating surface of the double-sided wiring printed circuit board 1, there are formed a mini bias through hole 2, wiring made of Cu foil 3, a component insertion hole 4, and a half through hole 9. This substrate 1 passes through a waterfall (curtain) 5 of a fluid solder resist at high speed. As a result, the protective layer (overcoat layer) 7 is uniformly applied except on the mini bias through hole 2, the half through hole 9 and the component insertion hole 4.
Once formed and dried and cured, the overcoat process is complete.

FIG. 2 is a view for specifically explaining the principle of uniform coating by the method shown in FIG. As described in (1) of the action column, the time t required for the portion of the width ΔX of the substrate 1 to pass through the solder resist falls.
Is t = ΔX / V, and the solder resist amount falling on the substrate during that time is S · t = S · (ΔX
/ V). Therefore, the flow rate S of the solder resist
By changing cm ³ / sec or the moving speed V of the substrate, it is possible to accurately change the amount of resist applied on the substrate per unit time. That is, it is possible to set an arbitrary film thickness. Further, since the solder resist falls from the substantially vertical direction over the entire width of the substrate 1,
No coating unevenness occurs in the lateral direction of the substrate. Further, since the substrate 1 penetrates the waterfall of the solder resist at a substantially right angle at the speed V, the solder resist that has dropped onto the coating surface of the substrate 1 is evenly distributed in the vertical direction (rearward) of the substrate by the inertial force. Will be postponed. Therefore, a uniform solder resist film having an arbitrary film thickness can be formed with good controllability. 1 protective layer for solder resist
It can be formed freely and accurately up to about 50 μm.

FIG. 3 is a diagram for explaining the reason why the resist does not flow into the mini bias through hole 2, the half through hole 9 and the component insertion hole 4 when the solder resist is applied by the method shown in FIG. is there.

As described in the section (2) of action, as shown in FIG.
For example, when the solder resist 21 covers the mini bias through hole 2 as shown in (a), as shown in (b) of FIG.
A uniform pulling force is created by the surface tension, which causes
The solder resist ruptures and the opening of the through hole is automatically secured. The same applies to the component insertion hole.
That is, it is not necessary to remove the solder resist filled in the component insertion holes after forming the protective layer.

FIG. 4 is a diagram showing a configuration example of an apparatus for carrying out the method of FIG. In this apparatus, the substrate 1 is conveyed leftward at high speed by the conveyor 11 on the substrate delivery side (velocity V), and eventually, in accordance with the law of inertia, the movement of the solder resist is maintained while maintaining the movement of the velocity V. The waterfall 5 is cut through, received, landed on the conveyor 12 on the side, transported as it is, and stored in the stocker 16.

The liquid solder resist is stored in the tank 13 and has a flow rate adjusting means (for example, a cock) 1
It falls vertically through 4 to form a waterfall 5. The dropped solder resist is collected, and the tank 15 is collected by the pump 15.
Feedback is given to 3.

The drive rollers 10a and 10b of the conveyor 11 on the substrate feeding side and the conveyor 12 on the receiving side are respectively driven by a motor 18, and rotation of these motors and the flow rate at the outlet of the tank 13 are performed. The operation of the adjusting unit 14 is controlled by the control unit 17 as a whole. As a result, the operator can freely set a desired flow rate and speed in the control unit 17 and arbitrarily control the film thickness of the solder resist to be applied.

Therefore, according to the coating method of the present embodiment, by measuring the relationship between the flow rate and speed and the coating film thickness in advance and recording the data, anyone can
The coating layer having a desired film thickness can be easily formed. Further, since it is a non-contact type coating, a high degree of skill such as screen printing is not required, and the operator sets the flow rate and speed according to the coating film thickness from the control unit 17, and the substrate 1 is set on the conveyor 11. All you have to do is place it.
As a result, the work can be simplified.

FIG. 5 is a diagram showing an example of a sectional structure of a double-sided printed wiring board (a state after patterning the solder resist after curing) formed by using the apparatus of FIG. The protective resist layer 21 of the solder resist in the printed wiring board shown in the figure has a thickness of, for example, 150 μm.
Thus, the printed wiring board has a high withstand voltage and a high noise shielding effect.

FIG. 6 is a flow chart showing the outline of the manufacturing process for manufacturing the printed wiring board of FIG. That is, after the basic processing of the double-sided printed wiring board (step 40), the protective layer is formed by the method of the present embodiment described above (step 41), the component mark is formed (step 42), and the product is shipped to the customer. .

FIG. 7 is a diagram showing an example of a sectional structure of a low-priced printed wiring board which is manufactured by using the coating method of the present embodiment and has a high shielding effect against radiation noise. The feature of this substrate is that the conductive resin layer (electromagnetic shielding layer) 41 is
That is, it has a structure in which it is sandwiched between the insulating layer 40 and the protective layer 50.

FIG. 8 is a flow chart showing an outline of the manufacturing process for manufacturing the printed wiring board of FIG.
First, after basic processing of the double-sided printed wiring board (step 60), an insulating layer is formed by the method of the present embodiment described above (step 61), and then a conductive resin paste layer is formed by screen printing (step 61). Step 62). Next, an overcoat layer is formed by the method of this embodiment (step 63), and a component mark is formed (step 6).
4), ship to customer.

(Embodiment 2) FIG. 9 is a plan view for explaining another aspect of the method for coating a printed wiring board according to the present invention.

The feature of this embodiment is that the wiring margin portion 20 around the mini bias through hole 2 is provided with a notch (slit) 71, and the waterfall (curtain) 5 of the fluid solder resist is passed at high speed. That is. As a result, the protective layer (overcoat layer) 7 is uniformly applied and formed except on the component insertion hole 4 and the half through hole 9, and at this time, only the mini bias through hole 2 is automatically filled. It Then, the applied layer is dried and cured to complete the overcoat process.

The slit 71 provided in the wiring margin portion 20 breaks the balance of the surface tension of the solder resist layer applied on the substrate surface and prevents the flow into the through hole, as described in the section (3) of the action column. Acts to encourage (Fig. 1
1 (a), (b)).

FIG. 10 is a view for explaining a preferable position of the slit 71 provided in the wiring margin portion 20. The wiring margin is originally provided to ensure the electrical connection between the conductive layer on the inner wall surface of the through hole and the wiring on the front and back surfaces even if the through hole and the circuit pattern on the front and back surfaces are misaligned. It is what has been.
Therefore, the slit 71 should not impair such an original function.

Therefore, it is necessary to avoid the direction in which the wiring 3 is drawn out in order to eliminate the risk of disconnection, and also to avoid both sides in order to secure a left and right margin. Therefore, as shown in FIG.
Is preferably provided on the opposite side of the wiring 3 in a range of about 60 ° centering on the through hole 2.

Further, the shape of the slit 71 breaks the balance of the surface tension of the solder resist, and the through hole 2
Since it is necessary to promote the inflow to the wiring margin portion 20
It is desirable that the shape reaches the mini bias through hole 2 from the outer periphery of the above, and that the width is substantially uniform from the viewpoint of easy slit processing.

[0050]

As described above, the present invention can obtain the following effects by adopting a novel coating method (flow coating) in the field of manufacturing printed wiring boards.

(1) Easily, while suppressing cost increase
In addition, it is possible to form a high-thickness film such as a solder resist with good controllability. As a result, the withstand voltage and the effect of suppressing radiation noise can be easily improved, and a printed wiring board equipped with a high-voltage circuit or a circuit requiring low noise can be provided at a low price.

(2) Further, at the time of coating,
You can easily control and execute the filling and opening of mini bias through holes, and the opening of component insertion holes and half through holes. By filling the miniature through-holes and shipping them, there is no risk that solder debris or solder balls will accumulate or chemicals such as plating solution will remain in the subsequent steps. Therefore, the reliability of the printed wiring board can be improved. (3) In addition, according to the coating method of the present invention, anyone can easily and easily measure a desired film by measuring the relationship between the flow rate and speed and the coating film thickness and recording the data. It becomes possible to form a thick coating layer. Further, since it is a non-contact type coating, a high level of skill such as screen printing is not required, and an operator only needs to set the flow rate and speed and place the substrate on the conveyor. As a result, the work can be simplified. (4) In the past, with inexpensive coating methods such as spraying and dipping, it was not possible to set a high film thickness of the solder resist, which made it impossible to use a highly penetrable water-soluble flux, resulting in the use of a paste. Due to the need for cleaning, it has not been possible to cope with the recent tendency toward dechlorofluorocarbons. On the other hand, in the present invention, since the high film thickness setting (20 μm to 150 μm) can be freely performed while maintaining the low cost, even with such an inexpensive printed wiring board, the use of the water-soluble flux having strong permeability is used. It is possible, and dechlorofluorocarbon can be realized by switching to water washing. That is, it becomes possible to supply an inexpensive and high-quality printed wiring board while cooperating with environmental protection. (5) With this, it is possible to establish a system capable of supplying a low-priced printed wiring board having high performance, which meets various requirements.

[Brief description of drawings]

FIG. 1 is a plan view for explaining a typical aspect of a method for coating a printed wiring board according to the present invention.

FIG. 2 is a diagram for specifically explaining the principle of uniform coating by the method shown in FIG.

3A and 3B are reasons why the resist does not flow into the mini bias through hole 2, the component insertion hole 4, and the half through hole 9 when the solder resist is applied by the method shown in FIGS. It is a figure for explaining.

FIG. 4 is a diagram showing a configuration example of an apparatus for carrying out the method of FIG.

5 is a diagram showing an example of a cross-sectional structure of a double-sided printed wiring board (a state after patterning a solder resist after curing) formed by using the apparatus of FIG.

FIG. 6 is a follow chart showing an outline of a manufacturing process for manufacturing the printed wiring board of FIG.

7 is a diagram showing an example of a cross-sectional structure of a low-priced printed wiring board manufactured by using the coating method of the embodiment shown in FIG. 1 and having an improved shielding effect against radiation noise.

8 is a flowchart showing an outline of a manufacturing process for manufacturing the printed wiring board of FIG.

FIG. 9 is a plan view for explaining another aspect of the method for coating a printed wiring board of the present invention.

FIG. 10 is a slit 7 provided in a wiring margin portion 20.
It is a figure for demonstrating the 1st preferable position.

11A and 11B are views for explaining the function of the slit 71 in FIG. 9 (function of filling the mini bias through hole 2).

[Explanation of symbols]

 1 Double-sided Wiring Printed Circuit Board 2 Mini Bias Through Hole 3 Cu Wiring 4 Component Insertion Hole 5 Fluid Solder Resist Waterfall 7 Protective Layer (Overcoat Layer) 9 Half Through Holes 10a, 10b Driving Roller 11 Sending Side Conveyor 12 Receiving Side Conveyor 13 Tank 15 Pump 16 Stocker 17 Controller 20 Wiring margin 21 Solder resist 71 Notch (slit)

Claims (5)

[Claims] 1. A liquid coating material is caused to flow down over a predetermined width to form a flow of the coating material whose flow rate is controlled downward from above, and the printed wiring board is moved at a predetermined speed. The coating material is moved in a predetermined direction and passed through the flow of the coating material in the middle of the movement path, whereby the coating material falling from above is applied almost uniformly on the printed wiring board, and the coating of the printed wiring board is covered. A method for coating a printed wiring board, which comprises: 2. The printed wiring board to be coated is
A double-sided printed wiring board in which circuit patterns are formed on the front and back surfaces, some of the circuit patterns on the front and back surfaces are electrically connected through through holes, and component insertion holes are provided. 2. The print according to claim 1, which has a viscosity such that the action of tension is not impaired, and the surface tension is used to prevent the coating material from entering the through hole and the component insertion hole. Wiring board coating method. 3. A wiring margin portion around the through hole on the front and back surfaces of the printed wiring board, and a notch (slit) reaching from the outer periphery of the margin portion to the through hole.
2. The cutout is provided to cause an imbalance in the surface tension of the coating material, and allows the coating material to flow into the through hole, thereby filling the through hole. Method of coating printed wiring board. 4. The method for coating a printed wiring board according to claim 1, wherein the coating material is a solder resist, and the thickness of the applied solder resist is 20 μm or more. 5. A double-sided printed wiring board in which a circuit pattern is formed on the front and back surfaces, and a part of the circuit pattern on the front and back surfaces is electrically connected through through holes. On the back side, a wiring margin around the through hole is provided with a notch (slit) reaching from the outer periphery of the margin to the through hole, and the through hole provided with the notch is the circuit pattern on the front and back sides. A printed wiring board, which is filled with a coating material that covers the printed wiring board.