JPH11330704A - Printed wiring board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve mounting density by using the via-hole of an outermost layer even for a part mounting via-hole. SOLUTION: The following processes are provided for a printed wiring board having a via-hole for performing electric connection between neighboring layers: (a) the process for forming a small hole for a via-hole extending to the via-pad at the lower layer; (b) the process which applies copper plating on the entire surface of the upper layer including the inside of the small hole for this via-hole; (c) the process for forming the via-hole and the circuit pattern in this copper plated layer; (d) the process for applying flax 62 on the entire surface of this circuit-pattern forming surface; (e) the process C for printing cream solder 64 on the applicable via-hole at the surface-mounting-part connecting position among the via-hole formed in the process; (f) the process for melting the cream solder by reflow soldering; and (g) the process for removing flax.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board having via holes for electrical connection between adjacent layers, and more particularly, to a printed circuit board having a via hole formed in the outermost layer, in which a cream solder is placed in a via hole for connecting a surface mount component. It relates to a filling method.

[0002]

2. Description of the Related Art In order to increase the component mounting density of a printed wiring board, a via hole (VIA HOLE) for interlayer connection has been reduced in diameter. For example, micro via holes having a diameter of 100 μm or less (referred to as μ via holes) have come to be used.

FIG. 3 shows a structure of a conventional via hole. FIGS. 3A and 3B are a plan view and a side sectional view showing a component mounting pad formed on the outermost layer connected to a via hole. FIG. 3B shows an IC as a surface mount component. In FIG. 3, reference numeral 10 is a multilayer printed wiring board, 12 and 14 are insulating plates, 16 is an inner circuit pattern, and 18 is an outer circuit pattern. Both circuit patterns 16 and 18 are connected by a via hole 20. The outer circuit pattern 18 has a via hole 2
A component mounting pad 22 connected to the “0” is formed. The leads 22 of the IC 24 are soldered to the pads 22.

In the conventional printed wiring board shown in FIG.
The via hole 20 provided in the outermost layer is connected to the component mounting pad 22.
To mount the components on this pad 22,
A via hole 20 and a component mounting pad 22 must be formed in the outermost layer. For this reason, there is a problem that the component mounting area is limited and it is difficult to increase the mounting density.

Therefore, a resin is filled in the via hole of the outer layer,
It has been proposed that a pad (via pad) is formed on the filled resin so that components can be mounted thereon (Japanese Patent Application Laid-Open No. Hei 9-116266). That is, it is a blind via hole (pad-on-via).

FIG. 4 shows the structure of this via hole. FIG.
In the figures, reference numerals 30 and 34 denote insulating plates, reference numeral 38 denotes a resin filled in a via hole, and reference numeral 40 denotes a via pad formed on the via hole.

[0007]

However, the method of filling a resin into the via hole has the following problems. (1) In order to reliably fill the resin in the via hole, it is necessary to perform a polishing operation in which the resin is filled to a depth equal to or greater than the depth of the via hole, and then the upper surface of the outer circuit pattern is aligned. (2) Since the filler is a resin, in order to form a via pad on the upper surface, it is necessary to perform copper plating for forming an outer layer circuit pattern and further perform copper plating.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a first object of the present invention is to fill a via pad on a via hole by filling cream solder in a via hole for connecting surface mount components on the outermost layer. Without forming
An object of the present invention is to provide a printed wiring board that enables connection of the surface mount components. A second object is to provide a method for manufacturing the printed wiring board.

[0009]

The present invention provides the following means for solving the above-mentioned problems.

That is, according to the printed wiring board of the present invention, in a printed wiring board having a via hole for making an electrical connection between adjacent layers, of the via holes formed in the outermost layer, solder is contained in the via hole for connecting a surface mount component. It is characterized by being filled.

Further, according to the method of manufacturing a printed wiring board of the present invention, in a printed wiring board having a via hole for making an electrical connection between adjacent layers, among the via holes formed in the outermost layer by the following steps, The connection via hole is filled with cream solder. (A) Step of forming via hole small hole reaching lower via pad (b) Step of applying copper plating to the entire upper layer including the inside of this via hole small hole (c) Forming via hole and circuit pattern in this copper plated layer Step (d) Step of applying a flux to the entire surface of the circuit pattern forming surface (e) Step of printing cream solder in the via hole corresponding to the surface mounting component connection position among the via holes formed in step c) (f) Reflow soldering (G) a step of removing the flux

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a printed wiring board according to the present invention; FIG. 1 is a diagram showing a first stage of an embodiment of the present invention, and FIG. 2 is a diagram showing a second stage of the embodiment.

In FIG. 1, reference numeral 50 denotes an insulating plate, and an inner layer circuit pattern 52 is formed on at least one surface thereof. This inner layer circuit pattern 52 is, for example, an insulating plate 5
It can be formed on a copper foil stuck to zero by a photoetching method. A circuit pattern 52 is provided on the insulating plate 50.
Is laminated (FIG. 1A).

The insulating plate 54 has small holes 56 for via holes.
Is formed (FIG. 1B). The small holes 56 can be formed by using a photo etching method or a laser. In the case of using the photo-etching method, a photosensitive resin is used as a material of the insulating plate 54, and a portion other than the small holes 56 is hardened by exposing and overlapping a photomask, and the resin in the small holes 56 is removed. (Photo via). In the case of the laser method, the laser beam can be processed by irradiating a laser having a small diameter to the position of the small hole 56 (laser via). The small holes 56 are formed on the pads of the inner circuit pattern 52.

Next, the upper surface of the insulating plate 54 is plated with copper (FIG. 1C). The copper plating layer 58 is formed by first applying electroless copper plating to the inner surface of the small hole 56 and the insulating layer 5.
4 is performed by applying electrolytic copper plating after imparting conductivity to the upper surface. An outer layer circuit pattern 60 is formed on the copper plating layer 58 (FIG. 1D). Thus, a printed wiring board is obtained.

A flux 62 is applied to the upper surface of the outer circuit pattern 60 (FIG. 2E). At this time, a large amount of the flux 62 is applied particularly to the via hole 56A so that the flux 62 enters the via hole 56A. It is preferable to use a liquid flux.

Since the liquid flux has good fluidity, it can be smoothly applied to the upper surface of the outer layer circuit pattern 60 to flow into the via hole 56A and expel bubbles in the via hole 56A to replace the flux 62. it can. After applying the flux 62 and removing the excess flux 62, a predetermined amount of the cream solder 6 is placed on the via hole 56 </ b> A (via hole for connecting a surface mount component).
4 is printed by a screen printing method (FIG. 2F).

According to the screen printing method, a metal mask having a large number of openings corresponding to via holes for connecting surface mounting components is prepared, and the metal mask is aligned with the via holes and fixed on the printed wiring board 70 by overlapping. And
The cream solder is supplied onto the metal mask, the cream solder is rolled by moving the surface of the metal mask with a squeegee, and a predetermined amount of cream solder is printed in each opening. Here, the cream solder 64 is obtained by mixing a powdery solder with a highly viscous flux to form a cream.

The predetermined amount of the cream solder 64 to be printed in the step (F) of FIG. 2 is such that the upper surface of the cream solder 64 is higher than the upper surface of the outer circuit pattern 60 after the cream solder 64 is melted by reflow soldering described later. It is set to be located in. In addition, it is desirable that this setting is such an amount that it is not necessary to print cream solder again at the time of mounting the surface mount component separately. By rubbing the cream solder 64 onto the surface using a squeegee,
Although the cream solder 64 is pushed into the via hole 56A, the cream solder 64 does not completely enter the via hole 64 due to its high viscosity, and a cavity 66 may be formed in the via hole 56A. However, this cavity 66 disappears by being replaced with cream solder by reflow soldering. The cream solder printing method is not limited to the screen printing method, but may be a dispenser method or a stencil method.

After the cream solder 64 is printed on the via holes 56A, the metal mask is peeled off from the printed wiring board 70. At this time, the printed cream solder 64 remains in the via hole 56A. If the cream solder 64 on the via hole 64 is melted by placing the printed wiring board 70 in a reflow furnace and heating,
The melted solder is reliably filled in the via hole 56A by the surface tension of the solder itself (at this time, the cavity 66 disappears by being replaced with cream solder). The position is automatically adjusted (self-alignment action), and the hemisphere is formed. become. Therefore, if the cream solder is solidified by cooling as it is, the solder bump 64A having a fixed height and a fixed shape is formed.
Is formed (FIG. 2G).

Next, the flux 62 is removed by washing (FIG. 2 (H)). Thus, the finally required printed wiring board 70A is manufactured. A surface mount component can be directly mounted on the solder bump 64A thus formed.

[0022]

As described above, in the printed wiring board according to the first aspect of the present invention, after the outer layer circuit pattern is formed on the uppermost layer, cream solder is printed in the via hole for connecting the surface mount component, and reflow soldering is performed. Accordingly, since the solder bump is formed in the via hole, it is not necessary to form the pad for connecting the surface mounting component at another position, and a highly reliable, durable printed wiring board having a high mounting density can be provided.

When this printed wiring board is used, solder bumps are formed in the via holes for connecting surface mount components, and cream solder sufficient to mount the components has been attached. Since it is not necessary to print the solder, the assemblability is improved and a low-cost printed wiring board can be provided.

According to the second aspect of the present invention, it is possible to provide a method of manufacturing the printed wiring board according to the first aspect.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first half of a process according to an embodiment of the present invention.

FIG. 2 is a view showing the latter half of the process.

FIG. 3 is a diagram showing a conventional via hole structure.

FIG. 4 is a diagram showing a conventional via hole structure.

[Explanation of symbols]

 50, 54 Insulating plate 52 Inner layer circuit pattern 56 Small hole for via hole 56A Via hole 60 Upper layer circuit pattern 62 Flux 64 Cream solder

Claims (2)

[Claims] 1. A printed wiring board having a via hole for making an electrical connection between adjacent layers, wherein a solder is filled in a via hole for connecting a surface mount component among via holes formed in an outermost layer. Printed wiring board. 2. A printed wiring board having a via hole for making an electrical connection between adjacent layers, wherein solder is filled in a via hole for connecting a surface mount component among via holes formed in an outermost layer in the following step. Manufacturing method of a printed wiring board. (A) Step of forming via hole small hole reaching lower via pad (b) Step of applying copper plating to the entire upper layer including the inside of this via hole small hole (c) Forming via hole and circuit pattern in this copper plated layer Step (d) Step of applying flux to the entire surface of the circuit pattern forming surface (e) Step of printing cream solder in the via hole corresponding to the surface mounting component connection position among the via holes formed in step c (f) Reflow soldering (G) a step of removing the flux