JP2001174401A - Bonded/joined structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an index for prescribing the strength of a bonded/joined structure excellent in versatility in order to facilitate the determination of a structure, the selection of a material and the determination and control of a process, and a method of determining the same. SOLUTION: More than two indexes for prescribing the relation between an imaginary opening displacement and stress in a bonded or joined interface are used not only to clear conditions to be satisfied in order to ensure the strength reliability of a product but also to facilitate the rational determination and control of a structure and a process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure having an adhesive or joint portion, and more particularly to an index of adhesion and joint strength, a display method, a written document, and an adhesive and joint structure.

[0002]

[Prior Art] Adhesion and joining technology development and productivity improvement,
Bonding and joining structures of dissimilar materials in a wide range from electronic devices such as semiconductor chips, resin-encapsulated semiconductors, wiring boards, electric devices such as motors and transformers, to vehicles and space devices, due to demands for weight reduction and miniaturization. Is used. In these bonding and bonding structures, bonding and bonding strength of a certain level or more are required to withstand the stress generated on the bonding surface due to various factors such as bonding, thermal expansion difference between the bonded body and adherend, and mechanical load. Required to have. For this reason, in designing and manufacturing the bonding and bonding structure, it is necessary to select an adhesive bonded body and an adherend that can secure the required bonding strength.

[0003] The strength of the bonded portion and the bonded portion is determined not only by the material of the bonded body and the adherend, but also by the surface treatment method, the environmental conditions such as temperature and humidity during bonding and bonding, and the voltage at the time of forming a thin film. It is necessary to select and manage these conditions depending on the joining conditions such as.

[0004] However, since there are many factors affecting the adhesion and the bonding strength, generally, the bonding strength is often obtained using a test piece obtained by bonding the same bonded body and the adherend in the same process as the product. In this case, it is often difficult to produce a test piece that can be tested under a stress state similar to that of a product or a test piece that can be tested under a typical stress state such as a tensile test, due to restrictions from the manufacturing method.

[0005] Even in such a case, there is no particular problem as long as a general-purpose index for defining the bonding and bonding strength is clear. For example, if stress can be used as an index of strength as in a normal structure, material selection, process control, and the like can be performed using allowable stress obtained from a test piece.

However, “Evaluation method of adhesive interface strength using stress singularity field parameter”: Transactions of the Japan Society of Mechanical Engineers (A) 5
As shown in Vol. 4, No. 499 (1988), p. 597, the stress at the end of the bond or joint that controls the strength shows a singularity. It is difficult to evaluate the bonding and bonding strength using only the index as an index. Furthermore, in the case of a bonded or bonded structure made of materials having different Young's moduli or Poisson's ratios, even when the bonded shape is smooth, the stress at the end of the bonded or bonded surface shows a peculiarity, and the stress at the bonded and bonded surfaces is not uniform Absent.

For this reason, it is difficult to obtain a simple tensile strength. Although the above-mentioned paper gives evaluation indices, the evaluation indices are different when the shape such as the joining angle is different, and the application range is limited because it is based on the theory of elasticity. Japanese Patent Application Laid-Open No. 3-4521 discloses a test method for determining the true adhesive strength, and an example in which the strength value obtained by this test method is indicated together with the adherend name. However, even in this example, the strength can be obtained only when a crack is present in the bonding portion, and the general bonding,
It cannot be applied to the case where no crack is included as in the case of a joint structure.

As described above, conventionally, there is no general-purpose evaluation index for the strength of the bonding and joining structures, and the lack of an appropriate evaluation index complicates the problem. In general, in the manufacture of a product, an evaluation amount is estimated in advance by calculation or the like with respect to a load applied to the product, and an adhesion, a bonding structure, and a process that can secure the strength reliability with respect to the evaluation amount are determined and managed. Unless the evaluation index is clear, it is not possible to determine and manage a reasonable structure and process. For this reason, the strength reliability of the bonding and joining structure must rely on a severe test of the actual product. However, if the evaluation index is not clear, it is not possible to clarify even if this severe test is appropriate.

[0009]

SUMMARY OF THE INVENTION As in the past, bonding,
If there is no appropriate index indicating the bonding strength, the following problem occurs.

(1) The conditions to be satisfied for ensuring the strength reliability of a product are not clear.

(2) Factors affecting the bonding / joining strength become unclear, making it impossible to determine and manage a rational structure and process.

(3) Even if there is test data obtained under the same material and bonding conditions for the adherend, the adhesive, and the bonded body, if the structure and the load conditions are different, the bonding and bonding strength can be accurately predicted. It is difficult to do.

As a result of (4) and (3), even if the adhesive performance is displayed on the resin material or the like due to stress or the like, effective data is not obtained.

(5) Adhesion and bonding strength, which have many influence factors,
Further, the database becomes complicated when the structure and the load condition are added as influential factors.

An object of the present invention is to provide an index for determining the strength of an adhesive or joint structure having excellent versatility and a method for determining the index, thereby facilitating the determination and management of the adhesive, joint structure, material and process. Is what you do.

[0016]

[Means for Solving the Problems] "Introduction to Fracture Mechanics" by Hiroyuki Okamura, Baifukan (Showa 51-5), As noted at 88, it is generally believed that failure occurs when the energy release rate reaches a certain value. The same applies to the bonding and joining parts. Therefore, the above problem can be solved by providing an index for defining an energy release rate that causes peeling at the bonding and bonding interfaces, and a method of calculating the index by calculation or the like. Conventionally, the energy release rate has been specified for shapes containing cracks, but it is not possible to specify the energy release rate for structures that do not contain cracks, such as sound bonding and joining structures. It was difficult.

This time, it was shown that the occurrence of delamination can be evaluated by expressing the energy release rate of the bonding / joining interface by the relationship between the virtual opening displacement of the interface and the stress. Therefore, the above object can be achieved by defining the relationship between the virtual opening displacement and the stress at the bonding or bonding interface as an index for determining the bonding or bonding strength.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a part of a printed circuit board. Copper foil 2 for wiring on both sides of substrate 1 made of epoxy and glass cloth
Is affixed. A resist 3 is lined on the copper foil. After patterning the resist 3, the copper foil is patterned by etching. Thereafter, an insulating resin film is bonded to the position of the resist 3 in FIG. It is necessary to ensure the adhesive strength of the copper foil for wiring with the base material, the photoresist at the time of pattern formation, and the insulating layer after the pattern formation. Therefore, the adhesive strength between the copper foil and the base material, the copper foil and the resist, and the adhesive strength between the copper foil and the insulating resin are specified. Hereinafter, this defining method will be described by taking an example of the adhesive strength between the copper foil and the resist.

As shown in FIG. 2, a resist 23 is formed on the copper foil 22.
Consider the case where is adhered. When a thermal stress or a mechanical load acts on the resist 23 and the stress or strain near the bonding end 24 becomes excessive, peeling occurs. This peeling does not occur purely at the interface, but occurs because the resist and copper near the interface increase in strain and break. It is assumed that displacement due to strain in a region involved in the formation of the fracture surface occurs at the interface. This is called virtual opening displacement. The interface strength is defined by the relationship between the virtual opening displacement and the interface stress. Various relationships can be considered between the virtual opening displacement and the stress at the interface.

However, in consideration of the accuracy of the actual strength test, it is simply considered as shown in FIG. This relationship can be expressed by two indices, a nominal maximum stress and a maximum opening displacement. The hatched portion in FIG. 3 indicates the energy release rate until peeling occurs.

In order to determine the required specification of the adhesive strength of the structure shown in FIG. 2, for example, a finite element analysis is used. An element representing the relationship between the virtual aperture displacement and the interface is referred to herein as an energy release element. The energy release element 25 is connected to the copper foil 2 of FIG.
A stress analysis is performed by inserting the stress into the interface between the resist 2 and the resist 23 to obtain two indices of a nominal maximum stress and a maximum opening displacement that can withstand an assumed load, and these are defined as required specifications of the adhesive strength.
As the energy release element, for example, an element that has a non-linear stress-strain relationship in a normal finite element can be used. In this case, the strain is obtained by dividing the virtual opening displacement by the element size.

The two indices of the nominal maximum stress and the maximum opening displacement that can withstand the assumed load are not only one set. If the nominal maximum stress is large, the maximum opening displacement may be small,
If the nominal maximum stress is small, the maximum opening displacement must be large. Therefore, the required specification of the adhesive strength is given as a relationship between the nominal maximum stress and the maximum opening displacement as shown in FIG.

On the other hand, the fact that the adhesive structure produced in the actual process satisfies the required specifications is shown as follows.

In the process of manufacturing a printed circuit board, several types of patterns having a line width are experimentally manufactured in order to check the resolution of a photoresist pattern. Using this, a shear peel test can be performed to examine the adhesive strength. Since similar patterns are made even with wiring metal films made on silicon,
Similarly, the joining strength can be checked.

As shown in FIG. 5, a load edge 6 is applied to the side surface of the resist pattern 5 formed on the copper foil 2 and is pressed by a load cell 7 to apply a load to cause shearing and peeling. As a result, a relationship between the line width and the peeling load is obtained as shown in FIG. By the same calculation as when the required specification of the adhesive strength is obtained for the test condition of FIG. 5, the nominal maximum stress and the maximum opening displacement that can obtain the result of FIG. 6 are obtained. Since there are two indices to be obtained, these indices can be determined by using two points of the relationship between the line width and the peeling load.

[0026]

[Table 1]

The nominal maximum stress and the maximum opening displacement obtained in this way are shown by A in Table 1. That is, the bond strength obtained from the test results in FIG.
The maximum opening displacement is 0.94 μm. This value exceeds the required specifications as indicated by the black circles in FIG. 4, and this bonding structure and bonding process satisfy the requirements for strength.

Using the nominal maximum stress and the maximum opening displacement obtained here, a calculated value is obtained in which the relationship between the line width and the peeling load coincides with the peeling test result over the entire line width as shown in FIG. 6A. . This indicates that the evaluation index proposed here can be applied irrespective of the line width and has versatility. For reference, the relationship between the line width and the peeling load with respect to the condition indicated by B in Table 1 is shown as B in FIG.

Considering the definitions of the nominal maximum stress and the maximum opening displacement shown in FIG. 3, the energy release rate of A is about seven times that of B. Now, in order to keep the maximum opening displacement of B as it is and keep the energy release rate the same as that of A, it is necessary to increase the nominal maximum stress by about 7 times. In this case, the relationship between the line width and the peeling load is 7 times B in FIG. This is clearly different from the curve of A. This indicates that even if the energy release rate is the same, the characteristics of the adhesive strength are not the same, and two or more indices are required to express the characteristics of the adhesive strength as in the present invention.

Further, "Evaluation method of adhesive interface strength using stress singularity field parameter": Transactions of the Japan Society of Mechanical Engineers (A) 54
Volume 499 (Showa 63-3), p. 597. When the index is selected so that the peeling load matches the test result when the line width is large, the relationship between the line width and the peeling load is obtained. Is as shown in FIG. 6 as the conventional method, which differs from the test result. For this reason, in the past, the adhesive strength was inferred from the test results of those having similar dimensions and shapes, or was determined by a relative comparison with those having proven results.

Another embodiment will be described with reference to FIGS. FIG. 7 is a cross-sectional view of the resin-sealed semiconductor. Sealing resin 1
1 is bonded to the semiconductor element 8, the tab 9, and the lead 10. This bonding needs to withstand the stress generated by the heat load during the reliability test, and in designing a resin-sealed semiconductor, it is important to select a resin or an adherend that can ensure the bonding strength. Therefore, if an index relating to the adhesive strength is described in the characteristic table of the resin or the lead material, it is useful for selecting the resin or the adherend.

FIG. 8 is an example of a document describing the characteristics of the amount of resin material describing the nominal maximum stress and the maximum opening displacement, which are indicators of the adhesive strength according to the present invention. Since the general property index of the adhesive strength is described together with the name of the adherend in the characteristic description document, it is possible to determine by calculation whether or not the product using the index satisfies the design specifications. Thus, by using the index of the adhesive strength of the present invention, the adhesive strength once determined can be widely used regardless of the structure.

The index of the adhesive strength of the present invention can be obtained from any test that can be analyzed and can obtain the strength under two or more conditions. For example, as shown in FIG. 9, a test piece in which two adherends 12 and 13 are joined by an adhesive 14 and a crack 15 is formed at a joint between the adherend 12 and the adhesive 14 is obtained.
By obtaining the relationship between two or more crack lengths and peel strength, two indices can be obtained.

[0034]

According to the present invention, a general-purpose evaluation of the bonding and bonding strength is achieved by using an index for defining the relationship between the virtual opening displacement and the stress at the bonding or bonding interface as an index for specifying the bonding and bonding strength. Becomes possible. As a result,
The conditions to be satisfied for ensuring the strength reliability of the product are clarified, and the rational structure and process can be easily determined and managed. Further, since this index does not include a factor of a structural shape or a load condition, it is easy to construct a database.

[Brief description of the drawings]

FIG. 1 is a sectional view of a part of a printed circuit board according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an implementation method of the present invention.

FIG. 3 is a characteristic diagram illustrating an index of the present invention.

FIG. 4 is a characteristic diagram illustrating an example of a required specification using an index of the present invention.

FIG. 5 is an explanatory view of a shear peel test method.

FIG. 6 is a characteristic diagram showing a relationship between a line width and a peel load obtained by a shear peel test and an index of the present invention.

FIG. 7 is a sectional view of a resin-sealed semiconductor.

FIG. 8 is an explanatory diagram of an example of a characteristic description document of a resin material in which a nominal maximum stress and a maximum opening displacement, which are indexes representing the adhesive strength according to the present invention, are described.

FIG. 9 is an explanatory diagram of an example of a test method for obtaining an index of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base material, 2, 22 ... Copper foil, 3, 23 ... Resist, 5 ...
Resist pattern, 6: load edge, 7: load cell,
8 semiconductor element, 9 tab, 10 lead, 11 sealing resin, 12 adherend, 13 adhesive body, 14 crack, 24
... adhesive end, 25 ... energy release element.

Claims (1)

[Claims] In a structure in which materials having different Young's moduli are bonded or bonded, as a strength characteristic of the bonding or bonding surface, a virtual opening displacement until stress of the bonding or bonding surface substantially increases and becomes zero again. An adhesive or bonding structure, characterized in that two or more indices defining the relationship between the stresses of the bonding or bonding surface are written, or a written document is attached thereto.