JPH1093251A - Method of machining multilayer printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of machining a multilayer printed board on which highly precise cutting can be conducted by a simple structure, without being affected by the variation in thickness of insulating resin. SOLUTION: In a multilayer printed board 1, the thickness of an insulating layer is measured, the part smaller than the center part of a rectangular part 111 of the insulating layer 3 is scraped off the depth shallower than the upper surface 21A of a guide piece 2A. After an insulating resin layer in only a slight thickness has been left on the upper surface 21A, the insulating resin layer on the guide piece 2A is removed by burning by projecting a laser beam, and the upper surface 21A of the guide piece 2A is exposed. Then, the scraping margin of the insulating layer 3 is measured, using the upper surface 21A of the guide piece 2A as the reference surface, the rectangular part 111 is scraped by a drill pit 15 using the upper surface 21A of the exposed guide piece 2A as the reference surface. The upper surface 21 of the internal layer circuit 2, ranging over the entire area of the rectangular part 111, is exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of processing a multilayer printed board for surface mounting an IC bare chip, that is, an LSI chip, on the multilayer printed board.

[0002]

2. Description of the Related Art Conventionally, in order to meet the demands for smaller and thinner electronic devices, substrates used in electronic devices have been developed.
LSI packages and multilayer printed boards of various shapes and structures have been devised. For example, as for an LSI package, a plastic QFP (quad flat package) is used as a mainstream of the LSI package having a large number of pins, but there is a limit in increasing the number of pins. Therefore, instead of the plastic QFP, a surface mount type LSI package having a large number of pins arranged in an array on the back surface has come to be used. Surface mount type L
As an example of an SI package, spherical solder is arranged in an array on the back surface of a multilayer printed circuit board to form input / output terminals, and an IC bare chip (LSI chip) is placed on the surface of the multilayer printed circuit board to form a resin. BG sealed with
A (ball grid array) is used.

A BGA is, for example, as shown in FIG.
On the back surface of the multilayer printed circuit board a, input / output terminals b formed by arranging spherical solders in an array are provided.
Place an IC bare chip (LSI chip) c on the surface of
The conductor (lead) d connected to the input / output terminal b and the IC bare chip c are connected with a bonding wire e, the outer conductor d is covered with a solder resist f, and the whole is covered with a sealing agent g made of resin. It is sealed. Although only the LSI package has been described above, a general multilayer printed circuit board on which an IC bare chip is mounted has a similar configuration.

[0004] As a means for shaving the portion of the multilayer printed circuit board on which the IC bare chip is mounted, machining is generally used. However, since the thickness of the insulating resin is not constant, the depth from the resin surface to the inner layer circuit is reduced. Therefore, there is a problem that excessive cutting or uncut cutting occurs. Means for solving this problem have been proposed, for example, as shown in FIG. 8, an inner layer circuit h, an outer layer circuit j provided outside, and an insulating layer k provided between both circuits h and j. After measuring the height w of the outer surface m of the multilayer printed circuit board a, the design value or the outer surface m of the multilayer printed circuit board a obtained by trial processing, etc. The depth s up to the outer surface n is cut by spot facing using the outer surface m of the multilayer printed circuit board a, which is the actually measured surface, as a reference surface. Also,
Japanese Unexamined Patent Publication No. 63-245995 discloses an electric circuit in which a drill pit and an inner layer circuit are brought into a conductive state by contact between the drill pit and the inner layer circuit, and detects the surface height of the inner layer circuit, that is, the cutting depth. It is cut by spot facing. Furthermore, a counterbore drill bit supported by the spindle support mechanism and a probe movable in the feed direction of the spindle of the spindle support mechanism are provided, and a high-frequency current is applied to the probe so that the inner layer circuit of the multilayer printed circuit board is provided. An eddy current is generated, a high-frequency magnetic field due to the generated eddy current is detected, and a distance between the drill bit and the surface of the inner layer circuit is calculated based on the strength of the detected high-frequency magnetic field. It is known to control the feed amount of the spindle based on the above.

[0005]

However, the conventional method for processing a multilayer printed circuit board requires a special measuring device and is expensive, and the outer surface of the multilayer printed circuit board often has insufficient smoothness. However, there is a problem that it is difficult to cut out the inner layer circuit with high accuracy. In the case of measurement using overcurrent, a special machine is required and the cutting machine becomes expensive, and the eddy current generated by the shape of the inner layer bonding terminal circuit of the multilayer printed circuit board becomes strong and weak, so that eddy current is generated. As a result, there is a problem that the distance between the drill bit to be calculated and the portion to be cut may not be accurately measured.
Furthermore, since the outer layer bonding terminal circuit is also formed of copper foil or the like on the front side of the multilayer printed circuit board, an eddy current may also be generated in the outer layer bonding terminal circuit and a high-frequency magnetic field may be generated. There is a problem that the distance between the drill bit and the part to be cut may not be accurately measured due to interference with the high-frequency magnetic field generated in the circuit.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of processing a multilayer printed circuit board capable of performing high-precision cutting with a simple structure without being affected by fluctuations in the thickness of an insulating resin. That is.

[0007]

In order to achieve the above object, a method for processing a multilayer printed circuit board according to the present invention is a method for processing a printed circuit board on which IC bare chips are surface-mounted.
After measuring the height of the outer surface of the insulating layer, the recess is formed by machining to a position slightly higher than the upper surface of the internal circuit to form a concave portion, and then the laser light is irradiated into the concave portion to form a concave portion. After removing the insulating layer remaining in the concave portion and measuring the height of the upper surface of the internal circuit exposed in the concave portion, the height of the upper surface of the internal circuit is used as a reference surface for processing, and the outer surface position of the insulating layer from the reference surface is determined. By cutting the insulating layer up to, the upper surface height of the inner layer circuit can be measured at the center position of the part to be cut out without being affected by the variation in the thickness of the insulating resin layer, so the place close to the circuit position to be exposed And the accuracy can be increased. In addition, no special configuration is required for the shaving machine, and no special processing accuracy is required for providing the insulating resin layer. This is a method of processing a printed circuit board on which an IC bare chip is surface-mounted, and a metal guide piece having the same thickness as the inner layer circuit is disposed at substantially the center of the mounting position, and the height of the outer surface of the insulating layer is measured. Thereafter, the upper surface of the internal circuit, that is, a portion slightly higher than the upper surface of the guide piece is cut out by machining to form a recess, and then the insulating layer remaining on the guide piece is irradiated with laser light in the recess. Remove,
After measuring the height of the upper surface of the guide piece exposed in the recess,
By setting the height of the upper surface of the guide piece as a reference plane for processing, and shaving the insulating layer from the reference plane to the outer surface position of the insulating layer,
It is possible to measure the top surface height of the guide piece with the same thickness as the inner layer circuit at the center position of the part to be cut without being affected by the variation in the thickness of the insulating resin layer, so it is measured near the exposed circuit position Accuracy can be improved. Also, there is no need for a special configuration for the cutting machine,
No special processing accuracy is required for providing the insulating resin layer. Further, by providing the guide pieces, it is sufficient to irradiate the laser light to the approximate center of the mounting position, so that the irradiation position of the laser light can be easily determined and the time required for the removal step by irradiation can be shortened.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 6 illustrates a multilayer printed circuit board manufactured by applying the processing method of the present invention. An inner layer circuit 2 is previously formed on one side surface of the substrate 1A of the multilayer printed board 1, and a resin layer 3 serving as an insulating layer is provided at an appropriate position thereon to expose a pad 20 which is a conductor portion of the inner layer circuit 2,
The other part is covered with an insulating layer 3 such as a resin.

In this embodiment, the IC bare chip 4 is placed between the pads 20 of the inner layer circuit 2 which is arranged to face each other.
The IC bare chip 4 and the pad 20 are connected by bonding using the bonding wire 5. Note that the pads 20 of the inner layer circuit 2 are not limited to those provided on both sides of the IC bare chip so as to be opposed to each other. The good is natural.

A step due to the thickness of the insulating layer 3 is formed around the IC bare chip 4 to form a flow prevention dam. When the sealing agent 6 such as resin is poured over the portion where the IC bare chip 4 is mounted, This prevents the sealant 6 from flowing out to unnecessary parts. The sealant 6 covering the portion where the IC bare chip 4 is mounted is poured in, and the IC bare chip 4, the bonding wires 5 and the pads 20 are covered and protected by the sealant 6. In order to connect the outer surface of the insulating layer 3 and the inner layer circuit 2, via holes 7 are formed at predetermined positions of the insulating layer 3.
After the inner circuit 2 is exposed in the via hole 7, the inner circuit 2 in the via hole 7 and the outer surface of the insulating layer 3 are electrically connected by plating 70,
An outer circuit 71 connected to the plating 70 on the outer surface of the insulating layer 3 is provided.

The outer circuit 71 has external pads 72 on the outer surface of the insulating layer 3 for connecting to electronic components and the like.
The legs of the electronic component 8 are soldered to the external pad 72 and the electronic component mounting pad 73 separately provided on the outer surface of the insulating layer 3. In the present embodiment, the case where the IC bare chip is provided only on one side surface of the multilayer printed circuit board has been described. However, the inner layer circuits are provided on both side surfaces of the multilayer printed circuit board, respectively. Of course, a bare chip can be provided. Further, instead of the electronic component 8, an IC bare chip can be connected.

An example of the processing method of the present invention will be described with reference to FIGS. In FIG. 2, an inner layer circuit 2 which is a conductor circuit adapted to component mounting and a guide piece 2A having the same height as the inner layer circuit 2 are provided substantially at the center of a rectangular portion 111 which is a mounting position on the surface of a substrate 1A of a multilayer printed circuit board 1. Is formed by etching or the like, and then a resin serving as an insulating layer is applied thereon to form an insulating layer 3 over the entire surface of the substrate 1A.
A circuit is formed on the outer surface 30 of the insulating layer 3 by etching, and the thickness of the insulating layer 3 in the multilayer printed board 1 formed by providing the outer layer circuit 71, the external pad 72, the pad 73 for mounting electronic components, and the like. H, that is, the distance H between the outer surface 30 of the insulating layer 3 and the inner surface 31 of the insulating layer 3 (the outer surface of the substrate 1A) is measured.

In FIG. 3, in the rectangular portion 111 on which the IC bare chip 4 is mounted, a smaller area including the approximate center of the rectangular portion 111 is to be exposed.
The insulating layer 3 is cut out from the outer surface 30 by the drill pit 15 of the counterbore processing device at a depth shallower than the upper surface 21 of the guide piece 2A and the upper surface 21A of the guide piece 2A. With a slight thickness t, and
To form Here, the residual thickness t of the insulating resin layer may be an appropriate value larger than zero, but is not more than の of the distance between the upper surface 21A of the guide piece 2A and the outer surface 30 of the insulating layer 3. It is good to

Next, as shown in FIG. 4, a laser beam R is radiated from the laser beam irradiating device 17 into the cut-out preliminary recess 16. Irradiation is performed on the portion where the guide piece 2A is located, that is, substantially at the center, to burn off and remove the residual insulating resin layer on the guide piece 2A. 21A
To expose. Note that the laser beam irradiation device burns off only the insulating resin layer without damaging the guide piece 2A. The upper surface 21A of the exposed guide piece 2A
By measuring the height of the upper surface 21A as a measurement reference plane (see FIG. 5), the amount of shaving of the insulating layer 3 located above the guide piece 2A, that is, above the inner layer circuit 2 is accurately measured. it can. Next, as shown in FIG. 1, the entire upper surface 21A of the exposed guide piece 2A is cut out and the whole rectangular portion 111 is cut out by the drill pit 15 as a measurement reference plane.
The upper surface 21 of the inner layer circuit 2 is exposed over the entire rectangular portion 111 to form a rectangular portion 111 on which the IC bare chip 4 is mounted.

According to the above configuration, since the upper surface 21 of the inner circuit 2 is irradiated with the laser beam R for burning off only the insulating resin layer, the upper surface 21 is not cut deeper than the upper surface 21 and a small range is sufficient. A small irradiation dose is required. Further, by irradiating the laser beam R, the insulating layer 3 in a necessary range can be easily and highly accurately removed, and the upper surface 21 of the inner layer circuit 2 can be reliably exposed. The upper surface 21 of the inner layer circuit 2 can be employed as a (measurement measurement reference surface). By measuring and confirming the height position of the upper surface 21 of the inner layer circuit 2, the thickness variation of the insulating layer 3 and the insulating layer 3 The shaving allowance can be accurately determined without being affected by the irregularities on the outer surface of the steel sheet, and a highly accurate shaving process can be performed. In addition, since the preliminary recess 16 has an area smaller than the rectangular portion 111 at the mounting position, high-precision cutting is not required, and simple and quick cutting can be performed. Further, no special configuration is required for the shaving machine, and no special processing accuracy is required for providing the insulating resin layer.

In the above embodiment, only the case where the guide piece having the same thickness as that of the inner layer circuit is provided is described. However, only the inner layer circuit may be provided without providing the guide piece. A position where the inner layer circuit at the mounting position is located below (usually, a peripheral portion of the mounting position) may be shaved to form a preliminary recess, and the bottom of the preliminary recess may be irradiated with laser light. According to this configuration, there is no need to provide a guide piece, and with a simpler configuration, without being affected by variations in the thickness of the insulating layer and irregularities on the outer surface of the insulating layer,
The cutting allowance can be accurately determined, and high-precision cutting can be performed.

[0017]

Since the present invention is configured as described above, it has the following effects. After measuring the height of the outer surface of the insulating layer, the recess is formed by machining to a position slightly higher than the upper surface of the internal circuit to form a concave portion, and then the laser light is irradiated into the concave portion to form a concave portion. After removing the insulating layer remaining in the concave portion and measuring the height of the upper surface of the internal circuit exposed in the concave portion, the height of the upper surface of the internal circuit is used as a reference surface for processing, and the outer surface position of the insulating layer from the reference surface is determined. By cutting the insulating layer up to, the upper surface height of the inner layer circuit can be measured at the center position of the part to be cut out without being affected by the variation in the thickness of the insulating resin layer, so the place close to the circuit position to be exposed And the accuracy can be increased. In addition, no special configuration is required for the shaving machine, and no special processing accuracy is required for providing the insulating resin layer. In addition, a metal guide piece having the same thickness as the inner layer circuit is provided at substantially the center of the mounting position, and the height of the outer surface of the insulating layer is measured. A recess is formed by machining to a slightly higher position to form a recess, and then the laser beam is irradiated into the recess to remove the insulating layer remaining on the guide piece, and the upper surface of the guide piece exposed in the recess is formed. After measuring the height, the height of the upper surface of the guide piece is used as a reference plane for processing, and by shaving the insulating layer from the reference plane to the outer surface position of the insulating layer, the variation in the thickness of the insulating resin layer is reduced. Without being affected, the height of the upper surface of the guide piece having the same thickness as the inner layer circuit can be measured at the center position of the portion to be cut, so that the measurement can be performed at a place close to the exposed circuit position, and the accuracy can be increased. In addition, no special configuration is required for the shaving machine, and no special processing accuracy is required for providing the insulating resin layer.
Further, by providing the guide piece, it is sufficient to irradiate the laser light only at substantially the center of the mounting position, so that the irradiation position of the laser light can be easily determined and the time required for the removal step by irradiation can be shortened.

[Brief description of the drawings]

FIG. 1 is an illustration of a method for machining a multilayer printed circuit board according to the present invention.

FIG. 2 is an explanatory diagram of a method for processing a multilayer printed circuit board according to the present invention.

FIG. 3 is an explanatory diagram of a method for processing a multilayer printed circuit board according to the present invention.

FIG. 4 is an explanatory diagram of a method for processing a multilayer printed board by laser irradiation according to the present invention.

FIG. 5 is an explanatory diagram of a method for processing a multilayer printed board according to the present invention.

FIG. 6 is a cross-sectional view illustrating an example of a surface-mounted LSI package to which the present invention is applied.

FIG. 7 is a cross-sectional view illustrating an example of a conventional surface mount LSI package.

FIG. 8 is an explanatory view of a conventional method for processing a multilayer printed circuit board.

[Description of Signs] 1 multilayer printed circuit board, 2 inner layer circuit, 3 insulating layer, 4
IC bare chip 5 bonding wire, 6 sealant, 7 via hole, 20 pads

Claims (2)

[Claims] 1. A method of processing a printed circuit board on which an IC bare chip is surface-mounted, wherein the height of an outer surface of an insulating layer is measured, and then the surface is cut out by machining to a position slightly higher than the upper surface of an internal circuit. After forming a concave portion, the insulating layer remaining on the upper surface of the internal circuit is removed by irradiating the concave portion with laser light, and the height of the upper surface of the internal circuit exposed in the concave portion is measured. A height of the substrate as a reference plane for processing, and exposing the inner layer circuit by shaving the insulating layer from the reference plane to the outer surface of the insulating layer. 2. A method of processing a printed circuit board on which an IC bare chip is surface-mounted, wherein a metal guide piece having the same thickness as that of an inner layer circuit is disposed substantially at the center of the mounting position. After measuring the height, the upper surface of the internal circuit, that is, a portion slightly higher than the upper surface of the guide piece is cut out by machining to form a concave portion, and then the laser light is irradiated into the concave portion and the concave portion is formed on the guide piece. After removing the remaining insulating layer and measuring the height of the upper surface of the guide piece exposed in the recess, the height of the upper surface of the guide piece is used as a reference plane for processing, and from the reference plane to the outer surface position of the insulating layer. A method for processing a multilayer printed circuit board, comprising: exposing an inner layer circuit by shaving an insulating layer.