JP3750914B2 - Method and apparatus for forming thin film on printed wiring board - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method and an apparatus for forming a thin film such as a photoresist layer on a printed wiring board in which a large number of through holes such as through holes are formed.
[0002]
[Prior art]
As a conventional method for forming a photoresist film having a uniform thickness on the entire surface of a printed wiring board, there is a method disclosed in Japanese Patent Application Laid-Open No. 5-67861. This is a method in which a substrate is immersed in a photoresist tank, a photoresist solution is applied to the entire surface of the substrate, pulled up, dried, rotated 180 degrees, and then immersed, pulled up, and dried once or more. . This method describes that a photoresist film having a relatively uniform film thickness can be obtained.
[0003]
[Problems to be solved by the invention]
However, the first drawback of this method is that through holes such as through holes or vias are filled with a resist material. The second drawback is that a photoresist film is formed on both sides of the printed wiring board. Therefore, if a photoresist film is formed only on one side, a masking process for masking one side of the printed wiring board is required. Is to become.
[0004]
The present invention solves such conventional problems, and a thin film on a printed wiring board in which a liquid material such as a photoresist material does not substantially enter the through hole of the printed wiring board or does not bleed out even if it enters. It is an object to provide a forming method.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, a liquid material such as a photoresist material is supplied to a printed wiring board in which a through hole is formed, and a rotation process is performed. In the method of forming a thin film having a desired film thickness that does not bleed through the back surface on one side of the printed wiring board, the printed wiring board is supported by a cradle so that a gap is formed on the lower surface of the printed wiring board. The liquid material is supplied to the center of the printed circuit board while performing the first rotation processing of the printed wiring board at a constant rotation speed or acceleration rotation speed, and after the supply of the liquid material is stopped, the first rotation processing is performed. The present invention proposes a method for forming a thin film on a printed wiring board, wherein the second rotation process is continuously performed at a rotation speed equal to or higher than the rotation speed of the first rotation process.
[0006]
According to a second aspect of the present invention, in order to solve the above-mentioned problem, in the first aspect, the liquid material is a photoresist material having a viscosity in a range of 10 cps to 2,000 cps, and the constant rotational speed is 100 rpm to 2. The present invention proposes a method for forming a thin film on a printed wiring board, characterized by being in the range of 1,000 rpm.
[0007]
According to a third aspect of the present invention, in order to solve the above-mentioned problem, in the first aspect, the liquid material is a photoresist material having a viscosity in a range of 10 cps to 2,000 cps, and the acceleration rotational speed is substantially increased with time. The present invention proposes a method for forming a thin film on a printed wiring board characterized by increasing within a range up to 2,000 rpm .
[0008]
According to a fourth aspect of the present invention, in order to solve the above-mentioned problem, in any one of the first to third aspects, the time required for the first rotation processing is longer than the time required for the second rotation processing. The present invention proposes a method for forming a thin film on a printed wiring board, which is characterized by the above.
[0009]
According to a fifth aspect of the present invention, in order to solve the above-described problem, the substrate according to any one of the first to fourth aspects is formed on the lower surface of the printed wiring board when the rotation process and the supply of the liquid material are performed. The present invention proposes a method for forming a thin film on a printed wiring board, wherein the air pressure in the gap is made higher than atmospheric pressure .
[0010]
Claim 6 of the present invention, for solving the above problems, in claim 5,
The present invention proposes a method for forming a thin film on a printed wiring board, wherein the air pressure is brought close to atmospheric pressure stepwise or continuously with the lapse of time of the rotation process .
[0011]
According to a seventh aspect of the present invention, in order to solve the above problems, a cradle for supporting a printed wiring board in which a through hole is formed, and a liquid supply nozzle for supplying a liquid material such as a photoresist material to the printed wiring board. In a thin film forming apparatus for a printed wiring board, comprising: a liquid supply apparatus comprising: a rotation driving device that rotates the printed wiring board supplied with the liquid material together with the cradle according to a predetermined rotation processing pattern; The cradle has a receiving part for supporting the printed wiring board, and most of the lower surface of the printed wiring board supported by the receiving part is separated from the upper surface of the cradle by 1 mm or more. A thin film forming apparatus for a printed wiring board is proposed.
[0012]
According to an eighth aspect of the present invention, in order to solve the above problems, a cradle for supporting a printed wiring board in which a through hole is formed, and a liquid supply nozzle for supplying a liquid material such as a photoresist material to the printed wiring board. in the thin film forming apparatus of a printed wiring board having a liquid supply device, and a rotary driving device for rotating in accordance with a predetermined rotation processing pattern supplied the printed wiring board together with pedestal above the liquid material having the The cradle has a receiving part for supporting the printed wiring board, and the receiving part has a bottom surface part that forms a gap serving as a pressure chamber between the lower surface of the printed wiring board and a side wall part extending therefrom. The bottom surface portion is provided with a plurality of small holes, and is provided with an air supply mechanism that can supply an air flow to the atmospheric pressure chamber through the small holes. It proposes a thin-film forming apparatus of a printed wiring board, characterized in that the pressure of the pressure chamber which is formed on the lower surface side of the wiring board is higher than the atmospheric pressure.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, when a uniform photoresist film is formed by rotating (spinning) a photoresist material on a printed circuit board having a through-hole, the photoresist material does not enter the through-hole or even if it enters. It does not turn to the back side through the through hole. A basic embodiment of the present invention will be described with reference to FIGS. A liquid supply nozzle 1 connected to a liquid supply mechanism (not shown) supplies a liquid photoresist material 3 to the center of the printed circuit board 2. The printed circuit board 2 is supported by four board support members 4a, 4b, 4c, and 4d provided on the cradle 4. The center portion of the cradle 4 is fixed to the rotary shaft member 5 and rotates together with the rotation of the rotary shaft member 5. Here, it is preferable that the substrate support members 4a to 4d be movable in the radial direction so as to be compatible with printed circuit boards of various sizes, and the number of substrate support members is not limited to four, but three or five. Etc.
[0015]
The supply of the liquid photoresist material 3 from the liquid supply nozzle 1 to the center of the printed circuit board 2 is performed in a state where the printed circuit board 2 is at a certain rotational speed or more as will be described later. When the liquid photoresist material 3 is supplied onto the printed circuit board 2 while the printed circuit board 2 is stopped, a pressure P acts on the liquid photoresist material 3 as shown in FIG. The material 3 tries to enter a through hole H such as a through hole or a via. Here, the pressure P is expressed by P = γh, where γ is the specific gravity of the liquid photoresist material 3 and h is the height of the photoresist material layer. On the other hand, an interfacial tension T acts between the liquid photoresist material 3 and the printed circuit board surface, and exerts a force against the force to put the liquid photoresist material 3 into the through hole H. Since the wettability between the liquid photoresist material 3 and the printed circuit board 2 is enhanced for the original purpose and the acting interfacial tension T is set to be low, the liquid photoresist material 3 is easily perforated. Enter H.
[0016]
Accordingly, in the present invention, the liquid photoresist material 3 is supplied from the liquid supply nozzle 1 to the center of the printed circuit board 2 in a state where the printed circuit board 2 is at a certain rotational speed or higher. In this case, when the movement speed of the liquid photoresist material 3 immediately above the through hole H of the printed circuit board 2 when the liquid photoresist material 3 spreads is v and gravity is g, it acts in the through hole H. It is clear that the pressure P becomes P = γh−γ v ² / 2g, which is smaller than when the printed circuit board 2 is stopped. Since the moving speed v increases in accordance with the rotational speed of the printed circuit board 2, the pressure P is set to a value at which the liquid photoresist material 3 does not enter the through hole H when the rotational speed is a certain value or more. it can. Further, after the liquid photoresist material 3 is supplied onto the printed circuit board 2, the liquid film material is instantly spread outward by the rotational force, so that the thickness of the liquid film is reduced, that is, h is reduced. As it expands, the pressure P decreases and it becomes difficult to enter the through hole H. Therefore, the liquid photoresist material 3 is likely to enter the through hole H in the vicinity of the center of the printed circuit board 2 to which the liquid photoresist material 3 is supplied from the liquid supply nozzle 1. When the resist material 3 is supplied, the printed circuit board 2 must be rotated at a certain rotational speed.
[0017]
Further, as shown in FIG. 2, if the distance between the printed circuit board 2 and the cradle 4 is not less than a certain level, the airflow as shown in the figure is easy to flow, and the lower surface of the printed circuit board 2 is prevented from becoming negative pressure. It is possible to prevent the liquid photoresist material 3 from being sucked into the through holes H. For example, when the printed circuit board 2 is placed on the cradle 4 and rotated, a minute gap exists between the printed circuit board 2 and the cradle 4 so that the gap is negative pressure. The liquid photoresist material 3 is sucked into the through holes H. However, according to various experiments, if the gap between the lower surface of the printed circuit board 2 and the upper surface of the cradle 4 is approximately 1 mm or more, the negative pressure is large enough to adversely affect the lower surface of the printed circuit board 2. It was confirmed that the liquid photoresist material 3 can be prevented from being sucked into the through holes H.
[0018]
Next, an embodiment of a thin film forming apparatus for applying a photoresist material or the like to a printed circuit board by rotation will be described with reference to FIG. 3, the same symbols as those used in FIGS. 1 and 2 indicate the corresponding members. The cradle 4 includes a base portion 4A fixed to the rotating shaft member 5 and a receiving portion 4B that receives the printed circuit board 2 and forms a pressure chamber. The base portion 4A has a square bottom surface portion 4A1 corresponding to the shape of the printed circuit board 2, and a hole 4A2 is formed at the center of the bottom surface portion 4A1, and the center axis of the rotary shaft member 5 matches the center of the hole. In this way, the rotary shaft member 5 is fixed. Base side wall of the outermost appropriate for height of four sides of 4A 4A3 is provided, the receiving part 4 B on the upper surface of the side wall 4A3 is fixed. The receiving portion 4B has a breathable bottom portion 4B1 made of a square plate material having a large number of small holes h or a plate material made of a porous material, and an appropriate height provided on the outermost side of the four sides of the breathable bottom portion 4B1. Side wall portion 4B2. A stepped portion 4B3 for receiving and holding the printed circuit board 2 is formed on the side wall portion 4B2. A gap 4C between the bottom surface portion 4A1 of the base portion 4A and the lower surface of the air-permeable bottom portion 4B1 of the receiving portion 4B forms an air passage through which air passes through a large number of small holes b almost uniformly. Further, the printed circuit board 2 mounted on the stepped portion 4B3 and the receiving portion 4B form a pressure chamber 4D capable of maintaining a pressure state higher than the atmospheric pressure. The rotary shaft member 5 has an air passage 5A in the center, and is coupled to a fixed air supply pipe 7 through a labyrinth seal portion 6 having a general structure capable of maintaining an airtight state in a non-contact manner. The rotating shaft member 5 is coupled to a driving device 8 such as a motor.
[0019]
Next, several methods for forming a photoresist film on the printed circuit board 2 will be described. First, the printed circuit board 2 is mounted on the stepped portion 4B3 of the cradle 4 and the liquid supply nozzle device (not shown) is operated to move the liquid supply nozzle 1 to the center of the printed circuit board 2. At this time, the rotation driving device 8 is operated to rotate the cradle 4 at a constant rotation speed or an acceleration rotation speed. In the method of the first embodiment, the air supply mechanism is not driven, the atmospheric pressure of the atmospheric pressure chamber 4D is not increased, and the atmospheric pressure is maintained, that is, the both sides of the printed circuit board 2 are at atmospheric pressure. A photoresist material 3 is supplied from the liquid supply nozzle 1. The photoresist material 3 used in this example has a viscosity in the range of 10 to 2,000 cps, preferably in the range of 50 to 1,600 cps. Then, as shown in FIG. 4, the photoresist material 3 is transferred from the liquid supply nozzle 1 to the printed circuit after time t1 when the rotation speed R1 is within a range of 100 to 2,000 rpm, preferably 300 to 1,700 rpm. The supply onto the substrate 2 starts, and at the time t2, the supply of the liquid material 3 is stopped and the rotation speed is increased to R2. As described above, first, the first rotation process in which the photoresist material 3 is supplied and processed at a constant rotation is performed in the period T1 between the times t1 and t2. Under this condition, the lower surface side does not substantially become a negative pressure state with respect to the upper surface side of the printed circuit board 2 due to the rotation.
[0020]
Here, when the viscosity of the photoresist material 3 is lower than 10 cps, the photoresist material 3 enters the through hole (not shown) of the printed circuit board 2 to the vicinity of the back surface even if the rotational speed is adjusted. It is not preferable. Further, when the viscosity of the photoresist material 3 is larger than 2,000 cps, the photoresist material 3 does not enter the through hole of the printed circuit board 2, but it remains on the printed circuit board 2 even if the rotational speed is adjusted. It is difficult to form a uniform film. Further, when the rotational speed R1 is 100 rpm or less, even if the viscosity of the photoresist material 3 is in the range of 10 to 2,000 cps, the lower viscosity of the photoresist material 3 does not pass through the printed circuit board 2. In the vicinity of the back surface. When the rotational speed R1 is 2,000 rpm or more, the film may not be formed at the through-hole portion or may be too thin.
[0021]
Next, after processing for a fixed time at a fixed rotation speed R2, the rotation speed is lowered to zero at time t3. The time T2 from the time t2 when the rotation speed starts to R2 to the time t3 when the rotation speed drops to almost zero is defined as the time required for the second rotation process. The time T2 of the second rotation process must be shorter than the time T1 of the first rotation process. Since the second rotation process is for further uniforming the thin film obtained by the first rotation process to obtain a desired film thickness, the time T2 of the second rotation process is set to the value of the first rotation process. If the time is longer than the time T1, the film may be too thin or a hole may be formed in the through hole portion of the printed circuit board 2, which is not preferable. By performing the rotation process under such conditions, almost no photoresist material enters the through hole such as the through hole of the printed circuit board 2, and even if it does not bleed out to the back surface of the printed circuit board 2. Thus, a photoresist film having a substantially uniform thickness can be formed on the printed circuit board 2.
[0022]
Next, a second embodiment will be described with reference to FIG. In this embodiment as well, as in the previous embodiment, all the rotation processes are performed while maintaining the atmospheric pressure without increasing the atmospheric pressure in the atmospheric pressure chamber 4D, that is, with both sides of the printed circuit board 2 being at atmospheric pressure. The photoresist material 3 also has a viscosity in the range of 10 to 2,000 cps, preferably in the range of 50 to 1,600 cps, as in the case of the above embodiment. In this embodiment, the photoresist material 3 is supplied from the liquid supply nozzle 1 to the printed circuit board 2 in the vicinity of time t1 when the rotational speed exceeds 100 rpm by acceleration rotation that linearly increases the rotational speed, and is determined in advance. At time t2 when the rotational speed r1 is reached, the supply of the photoresist material 3 is stopped, and the rotational speed r1 is held until time t3, and at time t3, it is started to increase to a predetermined rotational speed r2 higher than the rotational speed r1. Then, the printed circuit board 2 is rotated at a rotational speed r2 for a certain time, and the rotational speed is reduced to almost zero at time t4. The first rotation processing time T1 for accelerating and rotating the printed circuit board 2 while supplying the photoresist material 3 from the liquid supply nozzle 1 is longer than the second rotation processing time T2 for the same reason as in the above embodiment. long.
[0023]
In this embodiment as well, the photoresist material hardly enters the through-hole such as the through hole of the printed circuit board 2 and does not ooze out to the back surface of the printed circuit board 2 even if it enters. A photoresist film having a substantially uniform thickness can be formed. In this second embodiment, the rotational speed may be rapidly increased to 100 rpm to shorten the time until time t2, and the acceleration rotation that increases the rotational speed with time increases linearly with respect to time. As a matter of course, a linear increase in the number of revolutions that is curved with respect to time may be used. This is because a desired rotation can be easily obtained by storing various rotation patterns in the rotation drive device 8 and changing the number of rotations according to the input conditions. In these embodiments, the pattern of the second rotation process is substantially the same even if the number of rotations is increased in several stages other than the illustrated one, or the number of rotations is increased linearly with respect to time. It has been confirmed that the effect is obtained.
[0024]
In the above embodiment, since the atmospheric pressure chamber 4D formed between the printed circuit board 2 and the receiving portion 4B is rotated at the atmospheric pressure, the liquid material has a viscosity within the range of 10 to 2,000 cps. Although the photoresist material 3 is used, there is a case where a liquid material having a viscosity outside this range is applied to the printed circuit board 2 having the through holes to obtain a layer having a substantially uniform film thickness. In such a case, it was found that the air pressure in the air pressure chamber 4D may be made larger than the atmospheric pressure and the size adjusted.
[0025]
Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, the liquid material 3 having a viscosity smaller than 10 cps can be used, and the pressure in the pressure chamber 4D is adjusted mainly depending on the diameter of the through hole of the printed circuit board 2 and the viscosity of the liquid material 3. First, after mounting the printed circuit board 2 on the stepped portion 4B3 of the receiving portion 4B of the receiving base 4, an air supply mechanism (not shown) connected to the air supply pipe 7 is operated to allow air to pass through the small holes h of the breathable bottom portion 4B1. The pressure in the pressure chamber 4D is adjusted to a predetermined value. Thereafter, the liquid material 3 is supplied from the liquid supply nozzle 1 to the center of the printed circuit board 2 in a state where the printed circuit board 2 is rotated at a predetermined constant rotation speed. Set to zero. The rotation processing method may be the same as that of the above-described embodiment except for the rotation speed. In this embodiment, the rotation processing is performed at a predetermined constant rotation speed from the beginning to the end.
[0026]
As described above, the air flow depends on the diameter of the through hole of the printed circuit board 2 and the viscosity of the liquid material 3 as described above. As the diameter of the liquid material 3 increases and the viscosity of the liquid material 3 decreases, it is necessary to increase the atmospheric pressure. As a guideline for the adjustment, when the diameter of the printed circuit board 2 has a through-hole and the viscosity of the liquid material 3 is a certain value, the liquid material 3 enters the through-hole of the printed circuit board 2 as a result of the rotation process. In the case of wrapping around, it is necessary to increase the atmospheric pressure, and if the film made of the liquid material 3 is perforated by the air flow from the through holes or the film is lifted, the atmospheric pressure needs to be lowered. When the atmospheric pressure in the atmospheric pressure chamber 4D is preferably adjusted, the film made of the liquid material 3 is almost flat even in the through hole portion of the printed circuit board 2. In an actual apparatus, air does not leak from the through-hole when the through-hole of the printed circuit board 2 is covered with a film made of the liquid material 3 during the rotation process, but the printed circuit board 2 is mounted on the stepped portion 4B3 of the receiving base 4. Therefore, since air leaks from between the printed circuit board 2 and the stepped portion 4B3, it is necessary to send air to the pressure chamber 4D during the rotation process so as to maintain a predetermined pressure.
[0027]
For example, according to various experiments in the case of a through-hole having a diameter of 0.3 mm, the atmospheric pressure in the atmospheric pressure chamber 4D is adjusted to the above-described atmospheric pressure within a range not more than twice the atmospheric pressure. In addition, since the thickness of the film made of the liquid material 3 of the printed circuit board 2 becomes thinner as the rotation processing time elapses, the atmospheric pressure in the atmospheric pressure chamber 4D is finely adjusted continuously or stepwise in accordance with this. It is preferable to do this. This can be controlled in combination with a timer provided with valve means capable of finely adjusting the airflow in the air supply mechanism.
[0028]
【The invention's effect】
As described above, according to the present invention, a liquid material such as a photoresist material does not substantially enter the through hole of the printed wiring board, or even if it enters, it does not ooze out to the back surface, and is desired on one side of the printed wiring board. It is possible to form a thin film having a thickness of.
[Brief description of the drawings]
FIG. 1 is a view for explaining one embodiment of a method for forming a thin film on a printed wiring board according to the present invention.
FIG. 2 is a view for explaining one embodiment of a method for forming a thin film of a printed wiring board according to the present invention.
FIG. 3 is a view for explaining an embodiment of a thin film forming apparatus for a printed wiring board according to the present invention.
FIG. 4 is a view for explaining one embodiment of a method for forming a thin film of a printed wiring board according to the present invention.
FIG. 5 is a view for explaining another embodiment of a method for forming a thin film on a printed wiring board according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Liquid supply nozzle 5 ... Rotary shaft member 2 ... Printed circuit board 6 ... Labyrinth seal part 3 ... Liquid material 7 ... Air supply pipe 4 ... Receptacle 8 ... · Rotation drive device 4A ··· Base portion 4B ························· Base portion 4A1 of the base 4 ·· Base portion 4B1 · · Breathable bottom portion 4A2 · · Hole 4B2 on the bottom portion ··· Side wall 4A3 ·· Base side wall 4B3 ·· Step portion 4C of receiving portion ··· Gap (air passage)

Claims (8)

A liquid material such as a photoresist material is supplied to the printed wiring board in which the through holes are formed, and a rotation process is performed to form a thin film having a desired film thickness so that the liquid material does not bleed through the through holes to the back surface. In the method of forming on one side of
The printed wiring board is supported by a cradle so that a gap is formed on the lower surface of the printed wiring board, and the liquid state is performed while the printed wiring board is subjected to a first rotation process at a constant rotation speed or an acceleration rotation speed. The material is supplied to the center of the printed circuit board, and after the supply of the liquid material is stopped, the second rotation process is performed at a rotation speed equal to or higher than the rotation speed of the first rotation process after the first rotation process. A method for forming a thin film of a printed wiring board, comprising: In claim 1,
The method for forming a thin film on a printed wiring board, wherein the liquid material is a photoresist material having a viscosity in a range of 10 cps to 2,000 cps, and the constant rotational speed is in a range of 100 rpm to 2,000 rpm. In claim 1,
The liquid material is a photoresist material having a viscosity in the range of 10 cps to 2,000 cps, and the accelerated rotational speed increases within a range of up to about 2,000 rpm with time. Method. In any one of Claims 1 thru | or 3 ,
A method for forming a thin film on a printed wiring board, wherein a time required for the first rotation process is longer than a time required for the second rotation process. In any one of Claim 1 thru | or 4,
When the rotation process and the supply of the liquid material are performed,
A method for forming a thin film on a printed wiring board, wherein the air pressure in the gap formed on the lower surface of the printed wiring board is made higher than atmospheric pressure. In claim 5 ,
A method for forming a thin film on a printed wiring board, wherein the air pressure is gradually or continuously brought close to an atmospheric pressure as time of the rotation process elapses. A cradle for supporting a printed wiring board in which through holes are formed, a liquid supply device including a liquid supply nozzle for supplying a liquid material such as a photoresist material to the printed wiring board, and the print supplied with the liquid material In a thin film forming apparatus for a printed wiring board, comprising: a rotation driving device that rotates the wiring board together with the cradle according to a predetermined rotation processing pattern;
The cradle has a receiving portion for supporting the printed wiring board, the majority of the lower surface of the printed circuit board which is supported in the receiving part, and characterized in that apart than 1mm from the cradle of the upper surface A printed circuit board thin film forming apparatus. A cradle for supporting a printed wiring board in which through holes are formed, a liquid supply device including a liquid supply nozzle for supplying a liquid material such as a photoresist material to the printed wiring board, and the print supplied with the liquid material In a thin film forming apparatus for a printed wiring board, comprising: a rotation driving device that rotates the wiring board together with the cradle according to a predetermined rotation processing pattern;
The cradle has a receiving part for supporting the printed wiring board, and the receiving part has a bottom part forming a gap serving as a pressure chamber between the lower surface of the printed wiring board and a side wall part extending therefrom. The bottom surface portion is provided with a plurality of small holes, provided with an air supply mechanism capable of supplying airflow to the atmospheric pressure chamber through the small holes, and formed on the lower surface side of the printed wiring board during the rotation process. An apparatus for forming a thin film on a printed wiring board, wherein the atmospheric pressure of the atmospheric pressure chamber is higher than atmospheric pressure.

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