JP4140366B2 - Interlayer connection via hole inspection method and multilayer circuit wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for inspecting connection reliability of an interlayer connection via hole on which a semiconductor element is mounted, and a multilayer circuit wiring board.
[0002]
[Prior art]
In recent years, semiconductor devices such as semiconductor large-scale integrated circuits (LSIs) whose operating speed reaches 1 GHz in clock frequency have appeared. In such a high-speed semiconductor device, the degree of integration of transistors is high, and as a result, the number of input / output terminals may exceed 1000.
[0003]
In order to mount such a multi-terminal semiconductor element on a printed wiring board, a multilayer circuit wiring board called an interposer is arranged between the semiconductor element and the printed board, and is responsible for bridging the electrical connection between them. . The interposer has a wiring pattern having a very thin layer structure and fine lines and spaces than a printed wiring board in order to cope with bonding with terminals of highly dense semiconductor elements. Examples of interposers currently in widespread use include BGA (Ball Grid Array) and CSP (Chip Size Package).
[0004]
Recently, in order to respond to the demand for higher density mounting and higher operating frequency, the thickness of the entire interposer is reduced by laminating polyimide resin film and other wiring patterns, and the interlayer Some have been developed to cope with high frequencies by shortening the connection length.
[0005]
The electrical connection between the layers of the multilayer wiring pattern in the interposer is made by a minute columnar conductor called a via hole. Similarly to the wiring pattern, the via hole has a tendency that the via hole diameter is miniaturized and the aspect ratio (ratio of via hole diameter to length) is increased (to 1 to 1 or more) in order to cope with a higher operating frequency.
[0006]
A semiconductor package including an interposer on which a semiconductor element is mounted is often placed in a high temperature state during a solder reflow process during the manufacturing process or during operation after mounting in a device. Therefore, high reliability with respect to thermal stress load is required. In particular, the reliability of via-hole connection is important.
[0007]
Until now, a thermal cycle test has been widely performed as a reliability test for a thermal load of an interposer. In this test, a test temperature at a high temperature and a low temperature is set in advance, and the test piece is alternately exposed to a high temperature and a low temperature state at regular time intervals.
[0008]
However, in the case of an air tank type thermal cycle test that is widely performed, the time required from the start of the test to the occurrence of thermal fatigue failure is very long, and it often takes more than a month to complete the test. It was difficult to immediately check the quality of the finished product.
[0009]
On the other hand, although it is different from the thermal cycle test, a pull test has been widely performed as a method for inspecting the solder balls bonded to the surface electrode in BGA or the like and the bonding strength of the surface electrode itself (for example, patent documents). 1). After fixing the solder ball or surface electrode and the tip of the probe pin for pull test by various methods, the probe pin is pulled up until the solder ball or surface electrode peels off, and the load at that time is measured. It is a judgment of pass / fail.
[0010]
[Patent Document 1]
[Patent Document 1] Japanese Patent Laid-Open No. 8-11417
The joint (pull) test is an excellent method in that the quality of the product can be inspected immediately. Normally, this method is not applied because the via hole is not exposed on the surface but is buried in the insulating layer. It was difficult.
[0012]
[Problems to be solved by the invention]
The present invention has been conceived in view of the above circumstances, and an object of the present invention is to immediately inspect the connection reliability of the interlayer connection via hole in the multilayer circuit wiring board on which the semiconductor element is mounted, and the multilayer circuit wiring. Is to provide a board.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following measures.
That is, the invention of claim 1 is a method for inspecting the bonding strength of a via hole formed inside a multilayer circuit wiring board, and after isolating it from the periphery by forming a moat around the via hole to be inspected. The land electrode on the surface to which the via hole is connected and the probe pin for electrode joint strength test are joined, and the load when the probe pin is pulled up is measured and inspected.
[0014]
According to a second aspect of the present invention, in the method for inspecting the bonding strength of the via hole formed in the multilayer circuit wiring board, the object to be inspected is surely formed by forming a moat surrounding and surrounding the via hole to be inspected. The via hole is mechanically isolated from the surroundings, the land electrode on the surface to which the via hole is connected, and the probe pin for electrode bonding strength test are bonded, and the load when the probe pin is pulled up is measured and inspected.
[0015]
According to a third aspect of the present invention, in the method for inspecting the bonding strength of via holes formed inside a multilayer circuit wiring board, the depth of the moat is made shallower than the bottom surface of the internal conductor layer to which the via hole to be inspected is bonded. It is formed. Thereby, the strength of the joint portion of the via hole to be inspected is reliably measured and inspected.
[0016]
The invention of claim 4 is a method for inspecting the bonding strength of a via hole formed inside a multilayer circuit wiring board, wherein the area on the inner surface of the moat formed around the via hole to be inspected is larger than the area of the via hole, By ensuring a sufficient bonding area between the land electrode on the surface to which the via hole is connected and the probe pin for the electrode bonding strength test, the bonding strength of the via hole to be inspected is reliably measured and inspected.
[0017]
According to a fifth aspect of the present invention, in the method for inspecting the bonding strength of via holes formed inside a multilayer circuit wiring board, the distribution in the depth direction of the area inside the moat formed around the via hole to be inspected is at least via holes. The area at the junction depth is not larger than the value at other depth positions. As a result, the stress value at the depth position at which the strength is measured can be higher than that at other depth positions, and the bonding strength of the via hole to be inspected is reliably measured and inspected.
[0018]
According to a sixth aspect of the present invention, there is provided a method for inspecting the bonding strength of a via hole formed in a multilayer circuit wiring board, by forming a moat around the via hole to be inspected, The land electrode on the surface to which the via hole is connected and the probe pin for electrode bonding strength test are bonded, and the load when the probe pin is pulled up is measured to test the bonding strength of the via hole to be inspected. It is also possible to determine whether the joint strength is good or not by specifying a broken portion and comparing the difference between the portions.
[0019]
According to the seventh aspect of the present invention, if there is no via hole having a bonding strength (σ) of 100 MPa or less according to the method for inspecting an interlayer connection via hole according to any one of the first to sixth aspects, The characteristics can be satisfied.
[0020]
Accordingly, in the method for inspecting the connection reliability of the interlayer connection via hole in the multilayer circuit wiring board of the present invention as described above, the quality of the connection strength of the interlayer connection via hole is immediately inspected by taking the above-described means. It becomes possible to do.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a method for inspecting connection reliability of a multilayer circuit wiring board and interlayer connection via holes according to the present invention will be described below in more detail with reference to the drawings.
[0022]
FIG. 1 is a schematic cross-sectional view of a multilayer circuit wiring board used as a subject in this example in order to verify the operation and effects of the present invention. The conductor layer 1 has a total of four layers, and these layers are constituted by an insulating resin layer 2 and an adhesive layer 3. In this example, copper foil (thickness 12 μm), polyimide resin (thickness 13 μm), and epoxy resin (thickness 5 μm) were used for the conductor layer 1, the insulating layer 2, and the adhesive layer 3, respectively. A via hole 4 is formed for conduction between conductor layers. In this example, after forming a hole for the via hole 4 using an ultraviolet laser, the via hole 4 was formed by electrolytic copper plating. The via hole 4 had a diameter of 50 μm and a length of 20 μm. The material system, thickness configuration, and via hole dimensions to which the inspection method of the present invention can be applied are not limited to this embodiment.
[0023]
Next, a moat 5 was formed around the via hole 4 of this multilayer circuit wiring board. In the present example, an ultraviolet laser used for forming a via hole was used to form a trench 5 satisfying claims 2 to 5 as described below (see FIG. 2). That is, the shape of the moat was 50 μm wide, the depth was up to the surface of the inner conductor layer 6, and the inner area was 7.85 × 10 ⁻⁹ m ² constant in the depth direction. Specifically, the inner shape was circular with a diameter of 100 μm, and the area of the via hole with a diameter of 50 μm was larger than 1.96 × 10 ⁻⁹ m ² .
[0024]
In this embodiment, an ultraviolet laser is used, but a moat may be formed using a CO ₂ laser, an excimer laser, a mechanical drill, or the like. Further, the shape of the moat is not limited to this embodiment as long as the conditions of the claims are satisfied.
[0025]
Next, after a probe pin 8 for pull test is joined to the surface land electrode 7 as shown in FIG. 3, it is pulled up in the vertical direction (in the direction away) by a pull tester and joined to the via hole 4. The surface was broken and the load data at that time was recorded. In this example, a copper probe pin 8 having a radius of curvature of 100 μm and solder-plated at the tip was used and soldered to the surface land electrode 7. The probe pin lifting speed was 5 μm / sec. The joining means between the surface land electrode 7 and the probe pin 8 and the conditions of the pull test are not limited to the present embodiment.
[0026]
FIG. 4 shows load data acquired as a result of a pull test in a region including a via hole. It can be seen that the pull load gradually increased after the start of pulling up, and after reaching the maximum load value of about 40 gf, it decreased rapidly and the final fracture occurred.
[0027]
Further, as a result of conducting a pull test on a portion where a dug was formed in a portion where there was no via hole and only the insulating layer and the adhesive layer were present, the maximum load value was about 20 gf. Since the maximum load is clearly increased due to the presence of the via hole, it was confirmed that the bonding strength of the via hole can be measured with good reproducibility by the inspection method of the present invention.
[0028]
The bonding strength is “σ (region including via hole−insulating layer and adhesive layer only) = maximum load value (region including via hole−insulating layer and adhesive layer only) / via area at via bonding surface”. Desired. In this example, σ (region including a via hole with good electrical characteristics−insulating layer and adhesive layer only) = (40 gf−20 gf) /1.96×10 ⁻⁹ m ² = 102 MPa.
[0029]
In addition, when a pull test was performed on a region including the via hole of the multilayer circuit wiring board formed under the same conditions as in the example except that the time for performing the electrolytic plating was halved, the maximum load value reached about 30 gf. Later, it was found that the final break occurred. Therefore, σ (region including via holes with abnormal electrical characteristics—only the insulating layer and the adhesive layer) = (30 gf−20 gf) /1.96×10 ⁻⁹ m ² = 51 MPa.
[0030]
Therefore, the pass / fail judgment threshold is set to 100 MPa, and if a via hole lower than that value is detected, it is possible to immediately check that a problem has occurred in the manufacturing process at that time and the bonding strength has been reduced. It is.
[0031]
In addition, by embedding the extracted via hole sample in a resin to create a cross-sectional sample and observing it, or simply, the length of the extracted via hole has a length measuring function in the height direction. By measuring with an optical microscope or the like, it is possible to specify the actual fracture location. As a result, when a fractured portion different from that in the normal process is measured, it is possible to immediately check that a change has occurred in the process.
[0032]
【The invention's effect】
As described above, according to the present invention, it is possible to immediately inspect the connection reliability of the interlayer connection via hole in the multilayer circuit wiring board on which the semiconductor element is mounted.
[0033]
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view and a top view of a multilayer circuit wiring board.
FIG. 2 is a schematic cross-sectional view and a top view showing an example of a moat formed around a via hole.
FIG. 3 is a schematic cross-sectional view showing an example of a form of bonding between a surface land electrode and a probe pin tip when a via hole pull test is performed.
FIG. 4 is a graph showing a measurement example of a pull load value when a via hole pull test is performed.
[Explanation of symbols]
1 ... Conductor layer (copper foil)
2 ... Insulating layer (polyimide layer)
DESCRIPTION OF SYMBOLS 3 ... Adhesive layer 4 ... Via hole 5 ... Moat 6 ... Internal conductor layer 7 ... Surface land electrode 8 ... Tip part of a probe pin

Claims (7)

A method for inspecting the bonding strength of via holes formed inside a multilayer circuit wiring board, wherein the via holes are isolated from the surroundings by forming a moat around the via hole to be inspected, and then the via holes are connected. Bonding strength of the via hole by bonding the surface land electrode and the probe pin for electrode bonding strength test, moving the probe pin in a direction away from the land electrode, and measuring the load generated at that time A method for inspecting an interlayer connection via hole. 2. The method for inspecting an interlayer connection via hole according to claim 1, wherein the moat formed around the via hole is connected around the via hole to be inspected. The bottom surface of the moat is formed around the via hole according to claim 1 or 2 inspection method of the interlayer connection via holes, wherein the shallower than the bottom of the inner conductor layer via holes to be tested is bonded. Area of Horinouchi side formed around the via hole, the inspection method of the interlayer connection via holes according to claim 1, characterized in that larger than the diameter of the inspected holes. Area of Horinouchi side formed around the via hole, at least, to any one of claims 1 to 4 area of the junction depth of the via hole is characterized in that it does not become larger than the value of the other depth position Inspection method of interlayer connection via hole of description. 2. The interlayer connection via hole according to claim 1, wherein the tensile strength is detected to test the bonding strength of the via hole to be inspected, the final fracture location is specified, and the bonding strength is evaluated from the difference in the location. Inspection method. A multilayer circuit wiring board characterized in that a via hole having a bonding strength (σ) of 100 MPa or less does not exist by the method for inspecting an interlayer connection via hole according to claim 1.

Images