JP4863065B2 - Wiring board inspection method - Google Patents

Description

  The present invention relates to a wiring board inspection method.

  The IVH that reaches the circuit conductors of each inner layer formed by the conformal processing method of conventional multilayer printed wiring boards is uniformly laser drilled by the thickness of the workpiece, the coarse density of fibers such as glass cloth, the resin material, and the laser strength. It is difficult to process, and it is difficult to detect barrel-shaped IVH unless the substrate is destroyed, such as by observing a cross section.

As an example of conventional laser drilling, there is a method for manufacturing a multilayer printed wiring board disclosed in Patent Document 1.
This is a method of manufacturing a multilayer printed wiring board by the build-up method that forms IVH stacked in multiple stages while laminating resin-coated copper foil, and a reference mark that can recognize transmitted light from below the multilayer printed wiring board. This is a method for manufacturing a multilayer printed wiring board, which is provided on the first land for the first IVH and detects the transmitted light from the reference mark, thereby aligning and positioning the second IVH.
JP 2004-146427 A.

  In IVH laser drilling from the outer layer of the printed wiring board to the inner-layer circuit conductor of each step, the thickness from the outer layer to the inner layer of each step is the thickness of the insulating layer of each step, the thickness of the inner-layer circuit conductor of each step Also, the resin material is different, the coarse density of fibers such as glass cloth is different depending on the drilling position, and it is necessary to set the laser processing conditions by confirming the laser intensity and the number of shots of laser processing with several holes before work was there.

  However, in the unlikely event that there is a barrel-shaped IVH after laser drilling, there is no way to distinguish it, and because it is barrel-shaped, the IVH is a copper plating pretreatment and copper plating step that are the subsequent steps This causes a decrease in connection reliability or a disconnection due to poor liquid circulation in IVH.

  This invention provides the inspection method which discriminate | determines IVH which is a barrel shape efficiently from many IVH, without performing a destructive inspection.

The present invention is a wiring board inspection method performed by the following steps (a) to (c).
(A) A step of obtaining the above-mentioned maximum IVH inner diameter from an image obtained by photographing a wiring board having IVH in which one is released and the other is bottomed and performs electrical connection between layers and lands arranged around the IVH.
(B) A step of obtaining the IVH land diameter from the photographed image.
(C) A step of comparing the maximum IVH inner diameter obtained in the step (a) with the land diameter obtained in the step (b) and setting a flag when the IVH maximum inner diameter is larger than the land diameter.

  In the method for inspecting a wiring board according to the present invention, a barrel-shaped IVH is discriminated from a large number of IVHs without destroying the wiring board, and has an IVH that causes a decrease in connection reliability or a connection breakage. The outflow of defective products can be prevented.

  Further, if dummy IVH and land are provided in a discard frame portion different from the product substrate, the degree of IVH barrel shape of the product substrate can be grasped to some extent even if the product does not have a round land concentric with IVH.

  In addition, if the diameter of each of the dummy IVH and land is arbitrarily provided in the discarded frame portion, it is possible to know the occurrence rate for each degree of the IVH barrel shape without destroying the substrate. It is also possible to select a product having a higher quality IVH shape by setting a standard of degree.

  In the test for setting the laser processing conditions before the actual laser drilling, the substrate was conventionally destroyed by observing the cross section by observing the cross section, and the degree of the barrel shape was observed. If used, the degree of barrel shape of a large number of IVHs can be known with high work efficiency without destroying the substrate, and laser drilling conditions can be set efficiently.

The IVH described in the present invention means a hole in which one side is opened and the other side is bottomed, and electrical connection is made between two or more layers by a conductor.
More specifically with reference to FIG. 1, the conductor layer 2 arranged at the bottom of the insulating layer 1 becomes the bottom of the IVH, and the conductor layer 3 arranged at the top of the insulating layer 1 and the conductor layer described above. 2 are electrically connected by the plating layer 4 to form IVH5.

The land described in the present invention means a conductor formed on the open or bottomed surface of IVH and electrically connected to the peripheral wall of IVH.
More specifically with reference to FIG. 2, the conductor portion larger than the diameter of IVH5 is the land 6, and basically the land diameter is larger than the IVH diameter.
In addition, in the example described with reference to FIG. 2, the IVH 5 and the land 6 are circular in a top view and are concentric, but the present invention is not limited to this, and the IVH and the land have their shapes. Can be formed into a polygonal shape such as a triangle or a quadrangle, or a curved shape such as an ellipse.

The maximum inner diameter of the IVH described in the present invention means the diameter of the portion where the diameter is maximum from the bottom surface of the IVH to the open end of the IVH.
More specifically with reference to FIG. 3, the IVH 5 shown in FIG. 3 does not have a maximum open end diameter 7 but a maximum internal diameter 8 in a deeper portion.

  The image photographing described in the present invention means that the IVH image is recognized by X-ray photography or the like through which the maximum inner diameter of the IVH can be seen through, and further the automatic inner measurement of the maximum inner diameter of the IVH is performed.

In the image comparison described in the present invention, as shown in FIG. 4, the IVH maximum inner diameter (A) recognized by X-ray transmission or the like and the land diameter (B) are respectively measured, and (A) and ( It means comparing the length with B). The comparison is NG when the length of (A) exceeds the length of (B).
In the example shown in FIG. 4, three measurements from number 1 to number 3 are performed and displayed on the screen. Only number 1 is judged as NG. When NG is determined, a flag is set and notification is given by display, sound, device stoppage, and the like.
In the present invention, in the IVH conformal laser drilling method for connecting the layers of the multilayer printed wiring board, when the conductor land is formed and observed from the laser drilling direction, the conductor land and the IVH wall surface are substantially concentric. The difference in the size of the two diameters is used to change depending on the degree of the IVH barrel shape.

Further, processing conditions such as laser intensity and the number of laser processing shots are set for each material and thickness. In the case of the conformal processing method, the larger the laser intensity or the number of shots, the more the barrel shape protrudes from the copper that becomes the mask on the processing surface side.
In other words, the conductor land is formed with an arbitrary diameter on the IVH laser-processed by the conformal method, and the IVH maximum diameter and the land diameter are compared using X-rays or the like, and the degree of IVH barrel shape or laser This inspection method can determine the intensity, the number of laser shots, and the excess of the laser irradiation time.

  Further, when the IVH diameter is clearly larger than the land diameter, a hole 9 can be formed as shown in FIG.

Hereinafter, the laser processing method of the printed wiring board according to the present invention will be described with reference to FIGS.
As shown in FIG. 6, as a laser processing method of a printed wiring board, copper foil is laminated on both surfaces of a glass epoxy material 11, and this copper clad laminate is etched to form inner circuit conductors 12 and 13 on both surfaces. It becomes the provided core material 15.

Next, as shown in FIG. 7, a copper foil 17 is laminated on both surfaces of the core material 15 provided with the inner-layer circuit conductors 12 and 13 through a resin 16 by high-temperature press molding.
The surface of the copper foil 17 selects a portion to be IVH and removes copper by etching. After removing the copper, the removed portion is irradiated with a laser to provide a hole in the resin 16, and the remaining copper becomes a laser mask at that time.

  Next, as shown in FIG. 8, the carbon foil 17 is removed and the portion where the resin 16 is exposed is irradiated with a carbon dioxide laser (laser processing conditions: frequency 1000 Hz, pulse width 10 to 30 μsec). The via holes 25 and 26 having a diameter of 0.06 to 0.20 mm were formed by removing them by combustion decomposition.

Then, as shown in FIG. 9, electroless copper plating and electrolytic copper plating are performed, and plated conductors 27 are applied to the peripheral walls of the via holes 25 and 26 connecting the outer layer circuit conductor and the inner layer circuit conductor, and IVHs 28 and 29 are formed. Form.
Thereafter, the outer layer copper foil (outer layer conductor) is etched to provide predetermined outer layer circuit conductors 22 and 23.

Next, an embodiment of a laser processing method for a printed wiring board according to the present invention will be described with reference to FIG.
The cross-sectional view of FIG. 10 shows an enlarged cross-sectional view when processing the via hole 25 portion on the upper surface side in the laser drilling process in FIG.
The copper foil 17 is removed, the carbon dioxide laser is irradiated to the exposed portion of the resin 16, and the resin 16 is removed by combustion decomposition.

  As shown in FIG. 10, a carbon dioxide laser (laser processing conditions: frequency 1000 Hz, pulse width 10 to 30 μsec, beam diameter φ 0.2 mm) is shot 2 to 4 times to the portion where the copper foil 17 is removed and the resin 16 is exposed. (Irradiation), and the resin 16 having a thickness of 0.2 mm (in this example) is removed by combustion decomposition to the vicinity of the inner-layer circuit conductor 12.

  Next, as shown in FIG. 10, laser irradiation is continued until a part of the inner-layer circuit conductor 12 is exposed. At this point, the IVH is not yet barrel-shaped.

  After the inner layer circuit conductor 12 is exposed, the circuit conductor 12 is dissolved and decomposed. However, during processing of the inner-layer circuit conductor 12, dissolution and combustion decomposition is difficult, and the laser beam is reflected and diffused by the metal conductor. If excessive laser irradiation is performed from this point onward, as shown in FIG. 11, the resin 16 around the bottom surface of the via hole and the wall surface of the via hole is gradually burned and decomposed.

  That is, the excess laser irradiation energy from the time when a part of the inner-layer circuit conductor 12 is exposed is the cause of the IVH barrel shape.

It is sectional drawing explaining IVH formed by the laser processing method of the printed wiring board of this invention. It is the surface view and sectional drawing explaining IVH and its land which were formed by the laser processing method of the printed wiring board of the present invention. It is the surface view and sectional drawing explaining the IVH maximum internal diameter formed by the laser processing method of the printed wiring board of this invention. It is a simplified diagram of the equipment required to compare the IVH inner diameter formed by the laser processing method of the printed wiring board of the present invention and its land diameter. It is the figure explaining the example of barrel IVH (NG detection) which should raise a flag by comparing the IVH internal diameter formed with the laser processing method of the printed wiring board of the present invention, and the land diameter. It is sectional drawing of the front process explaining the laser processing method of the printed wiring board of this invention. It is sectional drawing of the front process explaining the laser processing method of the printed wiring board of this invention. It is sectional drawing of the front process explaining the laser processing method of the printed wiring board of this invention. It is sectional drawing of the post process explaining the laser processing method of the printed wiring board of this invention. It is an enlarged view explaining via hole processing by laser drilling of the present invention. It is sectional drawing explaining the example in the case of becoming barrel shape IVH.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulating layer, 2 ... Conductor layer, 3 ... Conductor layer, 4 ... Plating layer, 5 ... IVH, 6 ... Land, 7 ... Open end diameter, 8 ... Maximum inner diameter, 9 ... Hole, 11 ... Glass epoxy material, 12, 13 ... inner layer circuit conductor, 15 ... core material, 16 ... resin, 17 ... copper foil, 22, 23 ... outer layer circuit conductor, 25, 26 ... via hole, 27 ... plated conductor, 28, 29 ... IVH.

Claims (1)

A wiring board inspection method performed by the following steps (a) to (c).
(A) A step of obtaining the above-mentioned maximum IVH inner diameter from an image obtained by photographing a wiring board having IVH in which one is released and the other is bottomed and performs electrical connection between layers and lands arranged around the IVH.
(B) A step of obtaining the IVH land diameter from the photographed image.
(C) A step of comparing the maximum IVH inner diameter obtained in the step (a) with the land diameter obtained in the step (b) and setting a flag when the IVH maximum inner diameter is larger than the land diameter.

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