JP2719782B2 - Manufacturing method of multilayer printed wiring board - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a multilayer printed wiring board used for mounting electronic components of various electronic devices, and particularly to a non-through hole (hereinafter, referred to as a blind via). (Referred to as a hole). (Prior Art) With the recent increase in the degree of integration of electronic components, there is an increasing demand for higher density also in printed wiring boards on which these are mounted. As a method for increasing the density of a printed wiring board, attempts have been made to increase the number of layers and to increase the wiring density. With the increase in the number of layers, vias that are electrically connected between the layers and are not used for component mounting increase.However, since the via holes are through holes, in layers that are not electrically connected to the vias, The wiring must detour the via hole, which hinders a high wiring density. As a countermeasure,
The via hole is not a through-hole, and a buried via hole (inner layer via hole) is adopted for the connection between the inner layers, and a non-penetrating via hole (blind via hole) for the connection between the inner and outer layers. Has been adopted. One method of manufacturing a multilayer printed wiring board having a blind via hole is a method in which after lamination, a non-through hole is formed by drilling or laser, and plating is applied to electrically connect the inner layer and the outer layer. In this method, at least in the step of plating the blind via holes, if air bubbles remain in the blind via holes, the blind via hole wall surfaces in contact with the air bubbles cannot contact with each processing solution, plating solution, etc. Connection failure occurs because it cannot be formed. For this reason, air bubbles have been conventionally removed by ultrasonic cleaning or the like as a pretreatment of the plating step, but a sufficient effect has not been obtained for blind via holes having a high aspect ratio. (Problems to be Solved by the Invention) The present invention has been made in view of the above situation, and a problem to be solved is poor connection of blind via holes. The object of the present invention is to suppress the residual air bubbles in the blind via holes in the step of plating at least the blind via holes on the multilayer printed wiring board having the blind via holes, thereby suppressing the residual air bubbles. An object of the present invention is to provide a multilayer printed wiring board having a blind via hole with excellent connection reliability while suppressing the occurrence of unplated plating. (Means for Solving the Problems) Means taken by the present invention to solve the above problems are: a method of manufacturing a multilayer printed wiring board for plating blind via holes formed on the surface; Placing the printed wiring board in a sealable container, sealing and depressurizing the container; (b) injecting water or a liquid having a surface tension smaller than that of water and easily replacing water with water into the container; A step of immersing the whole multilayer printed wiring board; (c) a step of putting air into the container to return the pressure in the container to atmospheric pressure; and (d) removing the multilayer printed wiring board from the container and putting it into a plating step without drying. Process. In the method for manufacturing a multilayer printed wiring board, the water or liquid is injected using a reduced pressure from a tank disposed below the container, and the water or liquid is injected by the step of returning to the atmospheric pressure. Alternatively, there is provided a method for producing a multilayer printed wiring board, wherein the liquid returns to the tank. Next, a more detailed description will be given with reference to FIGS. 1 to 4 are diagrams showing one embodiment of a method for manufacturing a multilayer printed wiring board according to the present invention, and FIG. 5 is a diagram showing one apparatus for manufacturing a multilayer printed wiring board according to the present invention. It is. As a pretreatment for plating at least the blind via holes (2) of the multilayer printed wiring board (1) having the blind via holes (2), the multilayer printed wiring board (1) is put into a sealable container (11). (At this time, the valves A (15), B (16), and C (17) are closed.) After closing the lid (12) of the container, the valve A
Open (15) and operate the vacuum pump (13) to open the container (11)
And the valve A (15) is closed. Next, when the valve B (16) is opened, the water (or the liquid having a lower surface tension than the water in the tank (14) located below the container (11) shown in FIG. 6) is poured into the container (11), the entire multilayer printed wiring board (1) is immersed, and then the valve B (16) is closed. This injection is performed up to the level shown by the dotted line in the figure so that the water or liquid (6) does not reach the valves A (15) and C (17). At this time, air bubbles (7) remain in some blind via holes (2). Next, the valve C (17) is opened, and air is introduced into the container (11) to return the internal pressure of the container (11) to the atmospheric pressure. At this time, the bubble (7) in the blind via hole (2) contracts and becomes a minute bubble (8). Next, the lid (12) is opened, and the multilayer printed wiring board (1) is taken out of the container (1) and put into the next plating step without drying. In this plating step, the unplated portion generated by the bubbles (7) remaining in the blind via hole (2) becomes the unplated portion (9) due to the contracted micro bubbles (8). As the liquid (6) for immersing the multilayer printed wiring board (1) under reduced pressure, water is the most convenient because the subsequent plating step is usually a step using an aqueous solution, but the surface tension is smaller than water. In a liquid such as water or an organic solvent to which a surfactant capable of being easily replaced with water is added, bubbles (7) hardly remain in the blind via hole (2) due to its small surface tension, which is more effective. is there. However, when such a liquid is used, a water washing step for replacing the liquid remaining in the blind via hole (2) or the like with water before moving to the printing step is required. (Operation of the Invention) The present invention employs the above-described means to provide the following operation. In the present invention, since the multilayer printed wiring board having the blind via holes is immersed in a liquid such as water under reduced pressure, air bubbles remaining in the blind via holes at that time immerse the multilayer printed wiring board in the liquid. In the process of returning to the atmospheric pressure of the container pressure as it is, if the pressure is sufficiently reduced, the shrinkage reduces the residual bubbles sufficiently, so that the unplated portion generated by the residual bubbles also decreases sufficiently, and the blind vias are reduced. The connection reliability of the hole is not reduced. In addition, since a tank is provided below the container, if the pressure in the container is reduced, water or liquid is injected into the container, and if the pressure in the container is returned to atmospheric pressure, the water or liquid returns to the tank, so the process is remarkable. It's easy. (Example) Example 1 A six-layer printed wiring board having a blind through hole for electrically connecting an outer layer and an inner layer closest to the outer layer was produced by the following steps. Step 1: A necessary inner layer conductor circuit was formed on a glass-epoxy copper-clad laminate (thickness 0.3 mm, double-sided copper foil 35 μm) by a known tenting method, and an inner layer material was manufactured. Step 2: An 18 μm copper foil was adhered to both surfaces of the two inner layer materials so that two glass-epoxy prepregs were interposed therebetween, thereby forming a six-layer multilayer board. Step 3: A through hole was formed at a predetermined position by drilling, and then a blind via hole having a diameter of 0.3 mm was formed at a predetermined position at a depth of 0.3 mm by controlling the drilling stroke. Step 4: Put in a closed container, reduce the pressure to 2 mmHg, seal,
Water was poured into the container, and the entire multilayer board was immersed. Step 5: The internal pressure of the container was adjusted to atmospheric pressure by air injection, taken out, and charged to the next step without drying. Step 6: The whole of the multilayer board was subjected to chemical copper plating by the Shipley PTH process and then to known electroplating. Step 7: Outer layer patterning was performed by a known tenting method. The six-layer printed wiring board thus manufactured was evaluated for the connection reliability of the blind via hole. As a result, no connection failure occurred at the blind via hole. Example 2 In Example 1, steps 4 and 5 were changed to the following steps 4 'and 5', respectively. Step 4 ': After putting in a closed container, reducing the pressure to 2 mmHg and sealing, ethanol was poured into the container, and the entire multilayer board was immersed. Step 5 ': The inside pressure of the container was adjusted to atmospheric pressure by air injection, taken out, washed with water in an undried state, and then charged in the next step without drying. The six-layer printed wiring board thus manufactured was evaluated in the same manner as in Example 1. As a result, no connection failure occurred at the blind via hole. Comparative Example 1 In Example 1, steps 4 and 5 were omitted, and instead, step 8 shown below was performed. Step 8: Ultrasonic water washing was performed for 5 minutes, and the mixture was fed to the next step without drying. The six-layer printed wiring board thus manufactured was evaluated in the same manner as in Example 1. As a result, connection failure due to residual air bubbles occurred in 15 blind via holes out of 1,000 holes. (Effects of the Invention) As described in detail above, according to the present invention, as exemplified in the above embodiments, in a method for manufacturing a multilayer printed wiring board for plating blind via holes formed on the surface, a) placing a multilayer printed wiring board in a sealable container, sealing and depressurizing the container; (b) injecting water or a liquid having a surface tension smaller than that of water and easily replaceable with water into the container. And dipping the entire multilayer printed wiring board; (c) putting air into the container to return the internal pressure of the container to atmospheric pressure; and (d) removing the multilayer printed wiring board from the container and plating without drying. The process of putting into In the method for manufacturing a multilayer printed wiring board, the water or liquid injection is injection using the reduced pressure from a tank disposed below the container, and the water or liquid is injected by the step of returning to the atmospheric pressure. Alternatively, the liquid is returned to the inside of the tank, whereby the unplated portion generated by the residual bubbles in the blind via hole in the plating step has a size that does not pose a practical problem, and the connection reliability of the blind via hole is reduced. The property is not reduced. In addition, since the tank for storing water or liquid is arranged below the container, if the pressure inside the container is reduced, water or liquid is injected, and if the inside of the container is returned to atmospheric pressure, the water or liquid returns to the tank. Therefore, there is an effect that the process can be significantly simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 4 are partial cross-sectional views sequentially showing a method for manufacturing a multilayer printed wiring board according to the present invention, and FIG. 5 is a method for manufacturing a multilayer printed wiring board according to the present invention. FIG. 2 is a partial cross-sectional view illustrating an outline of an apparatus used for the present invention. DESCRIPTION OF SYMBOLS 1 ... multilayer printed wiring board, 2 ... blind via hole, 3 ... copper foil, 4 ... inner base material, 5 ... prepreg after curing, 6 ... water or surface tension is smaller than water Liquid that can be easily replaced with water, 7: air bubbles, 8: micro bubbles, 9: microplated uncoated portion, 10: plating film, 11
... container, 12 ... lid, 13 ... vacuum pump, 14 ... tank, 15 ... valve A, 16 ... valve B, 17 ... valve C.

Claims (1)

(57) [Claims] A method for manufacturing a multilayer printed wiring board in which blind via holes formed on the surface are plated, comprising: (a) placing the multilayer printed wiring board in a sealable container, sealing and depressurizing the inside of the container; (b) water Or a step of injecting a liquid having a surface tension smaller than that of water and easily replaceable with water into the container, and immersing the entire multilayer printed wiring board; (c) putting air into the container and reducing the pressure in the container to atmospheric pressure (D) taking out the multilayer printed wiring board from the container and putting it into the plating step without drying. In the method for manufacturing a multilayer printed wiring board, the water or liquid is injected using a reduced pressure from a tank disposed below the container, and the water or liquid is injected by the step of returning to the atmospheric pressure. Alternatively, a method for producing a multilayer printed wiring board, wherein the liquid returns to the tank.