KR20050098579A - Method for creating via holes in printed circuit board - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a via hole in a printed circuit board. In particular, an insulating layer is formed before copper plating on an inner wall of the via hole, so that migration between the vias and the vias is suppressed, thereby enabling the narrow via pitch to be realized. The present invention relates to a via hole forming method of a printed circuit board.

In addition, according to the present invention, a first step of drilling a panel to form a plurality of first bar holes; Filling and applying an insulating paste to the surface of the panel and the first via hole; A third step of processing a second via hole having a diameter smaller than that of the first via hole in the first via hole filled with the insulating paste; Performing a copper plating to impart conductivity to the second via hole; And a fifth step of forming a circuit pattern by performing an image forming process and a corrosion process on the panel.

Description

Method for creating via holes in printed circuit board

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a via hole in a printed circuit board. In particular, an insulating layer is formed before copper plating on an inner wall of the via hole, so that migration between the vias and the vias is suppressed, thereby enabling the narrow via pitch to be realized. The present invention relates to a via hole forming method of a printed circuit board.

Without software, a computer is simply a hard metal box. Likewise, no matter how many high-performance integrated circuits (ICs) and various electronic components are collected, they are not useful alone.

Properly arranged and electrically connected to each other and supplying power, such as electronic products that will operate as designed. As such, the PCB (Printed Circuit Board) is the basis for installing the electronic components, as well as electrically connecting the components.

Since the term PCB was formed by screen printing during the initial manufacturing process, the term Print was created.

At present, in the single-sided PCB manufacturing process, the printing ink is partially used, but since the wiring is formed using a photosensitive film or the like on both sides of the PCB, the term printed circuit board is not appropriate. It would be more desirable to call it an electronic circuit board. In East Asia, including Korea, the term PCB is used a lot, but in Europe, the term PWB (Printed Wiring Board) is used.

As mentioned above, the PCB also serves to mechanically fix the components in addition to the electrical connection between the electronic components. To increase mechanical strength, raw materials of PCBs contain about 50% glass fiber as a reinforcement material.

During the manufacturing process, the PCB is exposed to high temperatures of 200 ° C. or higher, requiring heat resistance that does not bend or deform the raw material.

Recently, with the development of computer and communication technology, the signal transmission speed has become an important parameter in electronic devices. Therefore, matching of impedance between components and wiring in PCB has become an important characteristic.

The goal of PCB design is always to increase functionality and component capacity. Since the beginning of most PCBs, engineers have tried to add more functionality and hence more interconnect traces.

These traces extend from one side to the other and from layer to layer, forming interconnections between active electronic devices in this way. PCBs have been made by many alternative materials and processes.

Most commonly used materials are laminates based on glass epoxy, and PCB structures are single-sided, double-sided, and multilayered (two or more layers).

The interconnect medium between layers is made by drilling a mechanical drill through the layers of the PCB to expose the copper interconnect lands on the individual layers.

The PCB then passes through the plating solution and the various layers are connected by plating or attached copper formed on the inner surface of the through hole. Perforated plating barrels that interconnect between these layers are called 'vias'.

The most obvious physical feature is that vias are rounded when viewed from the top or bottom. This is because it is formed by 'drilling'.

Drilling holes through the laminate results in round or circular holes. Hole drilling is performed by a drilling machine that drills using a 'drill', or a machine that rotates or cuts around the centerline to remove material around the centerline to make round or circular holes. The action of the drill is one of cutting.

As mentioned above, more and more interconnect traces have been required as circuits and thus the complexity of the PCB will be increased. This, of course, has led to a decrease in the size of the vias and an increase in the number of vias.

The new smaller vias are called 'micro vias' and represent a blind phenomenon. Blind vias are those vias that cannot fully pass through the PCB and stop at some preset layer depth.

Smaller via sizes are required due to an increase in trace density that reduces the point of a given layer where the terminal interconnect can be positioned to align with lands of other layers without interfering with the traces between the traces. do.

If the cross sectional area occupied by the via is reduced, the ability to use the via is similarly greater.

However, the reduction in via size means that mechanical drilling of micro vias is almost commercially complete. As several alternative processes, so-called laser ablation and plasma ablation methods have emerged.

Material removal is the electrochemical reaction of laser light pulses or plasma treatment. It is not a cutting action or treatment. However, similar removal removes the material surrounding the centerline.

This removal basically deals with mechanical drilling and superiority by making circular holes, whatever method is used. The rounded holes thus removed are often described as 'drilling' due to the removal of material around the centerline, so the term is referred to as micro via drilling.

A process of forming a printed circuit board via hole using a laser drill process according to the prior art is schematically illustrated in FIGS. 1A to 1D.

As illustrated in FIGS. 1A to 1D, the method of forming a via hole of a printed circuit board using a conventional laser drill process includes a laser drill process, a desmear process, and a copper plating process.

That is, in order to form a via hole of a printed circuit board, a via hole 102 penetrating two layers is first drilled into a copper-clad laminate 101 as shown in FIG. 1A as shown in FIG. 1B.

As shown in FIG. 1C, a desmear process is performed, and an inner wall of the hole is plated with a conductor such as copper to form a copper plating layer 103 to impart conductivity. After that, a circuit pattern is formed to complete the printed circuit board.

On the other hand, according to the prior art as described above, when the via beach is small, that is, narrow vial is processed, there is a problem that migration occurs between vias and vias. In other words, the insulating layer between the via and the via may be broken and electrically connected.

Therefore, when using the conventional method of forming the vial, it is difficult to overcome the current limit of 300 um, which is the processing limit of the via pitch.

Accordingly, the present invention has been made to solve the above problems, and provides a method for forming a via hole of a printed circuit board having an insulating layer inserted into the inner wall of the via hole before copper plating so that narrow via pitch can be realized. The purpose.

The present invention for achieving the above object is a first step of drilling a panel to form a plurality of first bar holes; Filling and applying an insulating paste to the surface of the panel and the first via hole; A third step of processing a second via hole having a diameter smaller than that of the first via hole in the first via hole filled with the insulating paste; Performing a copper plating to impart conductivity to the second via hole; And a fifth step of forming a circuit pattern by performing an image forming process and a corrosion process on the panel.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. 2A.

2A to 2F are flowcharts illustrating a method of forming a via hole of a printed circuit board according to an exemplary embodiment of the present invention.

The panel used in the method of forming a via hole of a printed circuit board according to an embodiment of the present invention uses a panel in which both conductive layers are removed, as shown in FIG. It is possible.

That is, the panel which can be used for this invention is a glass fiber base material (glass fiber reinforced preflag impregnated with the thermosetting resin composition) impregnated with the thermosetting resin composition, or the single side | surface or double-sided copper laminated board formed from the copper foil bonded to the one side or both surfaces. Include.

Printed circuit boards are typically manufactured from one or more basic structural blocks called panels in the industry. The panel is a sheet of a particular size that completely covers one or both sides of the dielectric layer and includes a conductive layer attached thereto.

Panels typically take the form of thin squares or rectangles with dimensions one side 300-700 mm long and less than 0.3 mm thick. The continuous conductive layer is collectively referred to as the covering material.

The panel dielectric layer is collectively referred to as the substrate layer. The coating thickness is usually in the range of 17 to 50 mu m, and copper is generally used as the coating material. The thickness of the base layer is usually in the range of 75 to 150 mu m, and a woven glass mat (glass-epoxy) impregnated with epoxy is generally used as the base material.

A printed circuit board is a sheet of a particular size and shape, and may be equipped with electrical members to provide a functional electronic device, for example, a computer storage component. The printed circuit board is provided as a mechanical support to the assembled electrical members such as capacitors, resistors and integrated circuit chips (ICs) to electrically connect them.

Printed circuit boards containing two or more ICs are referred to as multichip components (MCMs).

There are three types of printed circuit boards: single sided, double sided, and multilayered. The cross-sectional printed circuit board is composed of one dielectric substrate layer and one circuit layer. The circuit layer is a conductive layer of a printed circuit board that contains one or more electrical circuits that ground assembly parts, or that generate and ground large devices such as computers.

A backside printed circuit board includes one dielectric substrate layer and two circuit boards. The multilayered printed circuit board is a laminate of a dielectric layer, where the dielectric layer may be a dielectric substrate layer or a dielectric adhesive layer and a circuit layer.

Dielectric adhesive layers are generally used to join together multiple layers used to fabricate multilayer printed circuit boards. Before lamination, the dielectric adhesive layer, which is in film form, is commonly referred to as prepreg.

The circuit layer includes a form (ie, an electrical circuit) named as a conductor that forms a printed circuit. The conductor is the electrically conductive region of the circuit layer of the printed circuit board. Examples of conductors include lines, lands (areas where electrical members such as ICs, capacitors, and resistors are connected to a printed circuit board), vias (metal plated to connect two or more circuit layers). Holes) and annular rings. The annular ring is the conductor surrounding the via in the circuit layer. Generally, the circuit layer of a printed circuit board is produced in the coating material of a panel by the photoresist / etching process.

Conventional multilayer printed circuit boards are formed by stacking two treated panels comprising circuit layers on both sides. Such treated panels are typically laminated together using prepregs. In making printed circuit boards containing a glass-epoxy substrate, the prepreg is typically a partially cured glass-epoxy film.

Treated panels are further prepared for lamination by treating the circuit layer with a compound that promotes adhesion to the prepreg. An alternating layer of treated panel and prepreg is placed on the die. In addition to treated panels and prepregs, it is common to include a prepreg as the bottom and top layers in the die, and then a layer of metal foil (usually a copper layer).

The prepreg, treated panel and metal foil are laminated by applying heat and pressure to the die. Once laminated, the prepreg and metal foil provide the outer coating of the laminate. Subsequently, the laminate is processed by using the above-described backside printed circuit board process or a similar process to form a multilayer printed circuit board.

Next, a first via hole 202 is formed using a drill in the panel prepared as shown in FIG. 2B.

Excimer, Nd; YAG and CO ₂ type laser drill processing methods are most widely used to form via holes in printed circuit boards, and in the present invention, CO ₂ type laser drill processing methods are particularly preferable.

The excimer laser drilling method is rarely used for drilling a printed circuit board. The YAG laser drilling method using a wavelength of 355 nm can penetrate the copper plate directly. As much as 90% reflection occurs in the material containing the glass epoxy component, processing is difficult.

On the other hand, the laser drilling method of the CO ₂ type using a wavelength of about 9.4um exhibits an absorption rate of about 80% and can be processed.

Thereafter, as shown in FIG. 2C, the surface of the panel and the first via hole 202 are filled and surrounded with an insulating paste. As the paste, an insulating ink material is generally used.

Next, as shown in FIG. 2D, the second via hole 205 is processed using a drill. In this case, it is preferable to use a CO ₂ type laser drill method as described above. After drilling, deburring and desmear are performed to remove various contaminants and foreign matters generated during processing.

Here, deburring is an operation for removing dust particles on the burr and hole inner wall of the copper foil and dust, fingerprints, etc. on the surface of the copper foil generated during drilling. Another purpose of deburring is to increase the cohesion of copper in the subsequent plating process by imparting roughness to the surface of the copper foil.

In deburring, 'Buff polishing' is first performed using a brush (specially called a Buff brush) to obtain a frontal treatment effect. Next, two steps of washing with high pressure washing are performed to remove the particles falling off during the polishing process.

On the other hand, only a few revolutions per minute of the drill bit is rotated at high speed during drilling, which generates a lot of heat. Due to this heat, the resin constituting the PCB board melts and adheres to the inner wall of the hole, which is called a smear.

The smear must be removed as it plays a decisive role in degrading the quality of copper plating on the inner wall of the hole. This operation is called desmear in the sense of removing the smear.

In particular, multilayer PCBs tend to increase smear due to the generation of more heat than double-sided PCBs due to the copper foil of the inner layer. Desmearing is therefore a more important process for MLBs than for double-sided PCBs.

Then, copper plating is performed as shown in FIG. 2E. Copper plating is performed in the order of electroless copper plating from electroless copper plating.

Electroless copper plating is the only plating method for imparting conductivity to the surface of non-conductors such as resins, ceramics, glass, and the like. Electroless copper plating is plating on insulators, so reactions with electrically charged ions cannot be expected. Electroless copper plating is carried out by precipitation reactions, which are promoted by catalysts. To deposit copper from the plating solution, a catalyst must be attached to the surface of the material to be plated. This indicates that electroless copper plating requires a lot of pretreatment.

Electroless copper plating is generally difficult to thicken the plating film, and even the physical properties are less than the electrolytic copper plating, but in recent years, its properties have been greatly improved and its use has been expanded.

Electroless copper plating is performed by immersing the substrate in a plating solution so that not only the inner wall of the hole but also all parts of the substrate are plated. By performing electroless copper plating, the copper foil on the upper surface of the substrate and the copper foil on the lower surface are connected by a conductor. This is called primary copper plating. Primary copper plating is a primary plating for electrolytic copper plating, and the thickness of the plating film is also thin. The electroless copper plating film cannot be used as it is because of poor physical properties, and should be supplemented with electrolytic copper plating.

Electroless copper plating was performed to impart conductivity to the inner wall of the hole, and electrolytic copper plating using electrolysis is now possible. Electrolytic copper plating is easy to form a thick plating film, and the properties of the film are also superior to electroless copper plating.

Thereafter, as shown in FIG. 2F, the wiring pattern is formed by performing an image forming process and a corrosion process.

According to the present invention as described above, by suppressing the occurrence of the migration between the vias and vias, there is an effect to enable the processing of via holes having a narrow via pitch.

In addition, according to the present invention, it is possible to implement a narrow via pitch to overcome the current limit of 300um of the via pitch is effective.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

1A to 1D are views illustrating a process of forming a printed circuit board via hole using a laser drill process according to the prior art.

2A to 2F are flowcharts illustrating a method of forming a via hole of a printed circuit board according to an exemplary embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

201: Panel 202, 204: Via Hole

203: insulating paste 205: copper plating layer

Claims (3)

A first step of drilling a panel to form a plurality of first bar holes; Filling and applying an insulating paste to the surface of the panel and the first via hole; A third step of processing a second via hole having a diameter smaller than that of the first via hole in the first via hole filled with the insulating paste; Performing a copper plating to impart conductivity to the second via hole; And And a fifth step of forming a circuit pattern by performing an image forming process and a corrosion process on the panel. The method of claim 1, The panel, A via-hole forming method of a printed circuit board, characterized in that the glass fiber substrate impregnated with a thermosetting resin composition. The method of claim 1, The panel, A method of forming a via hole in a printed circuit board, the method comprising: a single-sided or double-sided copper laminated plate formed of a glass fiber substrate impregnated with a thermosetting resin composition and copper foil bonded to one or both surfaces thereof.