JP2003315177A - Internal stress measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal stress measuring method that can accurately measure an internal stress caused by an epoxy resin composition acting on a crystal in a molding. <P>SOLUTION: The internal stress measuring method, which is for a molding using an epoxy resin composition including no inorganic fillers with a crystal structure, and sealing in a crystal, computes an internal stress acting on the crystal in the molding from a difference between diffraction angles obtained when the crystal is irradiated with X rays before and after the sealing. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring internal stress. 2. Description of the Related Art In recent years, in the market trend of miniaturization, weight reduction, and high performance of electronic equipment, high integration of semiconductor elements is progressing year by year, and the size of semiconductor elements is increasing and wiring is becoming finer. . In the case of a semiconductor device in which such a semiconductor element is sealed with an epoxy resin composition, since the sealing layer, which is a cured product of the epoxy resin composition, comes into direct contact with the semiconductor element, the epoxy resin composition is cured by a temperature cycle. Strain stress is generated due to expansion and contraction of the object, causing problems such as displacement of wiring, cutting of bonding wires, and destruction of semiconductor elements. For this reason, it is necessary to accurately measure and analyze the internal stress acting on the semiconductor element in the semiconductor device, and to promote the development of an epoxy resin composition that can solve the above-mentioned problems. Conventionally, internal stress caused by an epoxy resin composition acting on a semiconductor element in a semiconductor device is caused by sealing the piezoelectric element with the epoxy resin composition similarly to the semiconductor element, and measuring the resistance of the piezoelectric element before and after sealing. There was a method of measuring the internal stress from the change in the resistance value by measuring the value, but the piezoelectric element is very delicate, and is greatly affected by the work process and the like when sealing the piezoelectric element. The results were poor in reproducibility. Further, as another method, there was a method of obtaining stress by computer simulation from the warpage of a semiconductor element by the finite element method. However, since only a calculation result in an ideal system was obtained, it could only be used as a reference value. . For this reason, there has been a demand for a method of accurately measuring internal stress acting on a semiconductor element sealed with an epoxy resin composition. SUMMARY OF THE INVENTION The present invention provides a method for measuring an internal stress which can accurately measure an internal stress caused by an epoxy resin composition acting on a crystal in a molded article. . [0005] The present invention provides an epoxy resin composition containing a crystalline structure and containing no inorganic filler,
In the method for measuring the internal stress of a molded article obtained by sealing a crystal, the internal stress acting on the crystal within the molded article is determined from the difference in diffraction angle obtained by irradiating the crystal before and after sealing with X-rays. This is a method for measuring internal stress, which is characterized in that it is calculated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The crystal according to the present invention refers to a slice obtained by cutting a silicon wafer and a semiconductor element.
The molded product is a product obtained by sealing the crystal, and includes a semiconductor device. X-rays used in the present invention include Co lines, Fe lines,
The type of line is not particularly limited as long as a diffraction phenomenon occurs in X-rays such as Cr line and Mo line. The X-ray generator may be one that can emit only characteristic X-rays or one that generates radiation such as a large accelerator.
Since it is necessary to detect the diffracted light through the sealing layer of the molded article, it is preferable to use an X-ray generator having a large generation output and an X-ray type such as Mo ray having a short wavelength. The method of measuring the diffraction angle of X-rays in the present invention may be either the parallel tilt method or the side tilt method since the crystal is a silicon single crystal. Depending on the direction of incidence of X-rays, either the fixed angle of incidence method or the fixed surface normal method may be used. There is no particular limitation as long as the method can measure the crystal structure of the crystal. The epoxy resin composition used for encapsulation in the present invention is an epoxy resin which is usually used for encapsulating a semiconductor,
An inorganic filler which does not contain a phenol resin, a curing accelerator and an inorganic filler having a crystal structure is an essential component. If an inorganic filler having a crystal structure is included, X-ray diffraction occurs at locations other than the crystal where the internal stress is measured, and accurate diffraction angles cannot be measured. Need to be used. Further, the cured product of the epoxy resin composition, that is, the sealing layer of the molded product must be free from substances that cause X-ray diffraction and scattering, such as antimony oxide, and must transmit X-rays. In the present invention, the internal stress acting on the crystal in the molded article is calculated as follows. The crystal before sealing is irradiated with X-rays, the X-ray diffraction angle θ ₀ is measured with an X-ray diffractometer, and X-rays are applied to a molded article obtained by sealing the crystal with an epoxy resin composition. Irradiate similarly, X
The diffraction angle θ of the X-ray was measured by a ray diffractometer. The difference between the diffraction angle θ and the diffraction angle θ ₀ is defined as Δθ (= θ−θ ₀ ). Since the difference in diffraction angle before and after sealing is required,
The internal stress σ in the vicinity of the surface of the crystal in the molded article is obtained based on the following formula. Internal stress σ = {E / 2} × ε _hkl = {E / 2} / T
anθ ₀ × Δθ Here, E represents the Young's modulus of the crystal, υ represents the Poisson's ratio of the crystal, and ε _hkl represents the distortion of the crystal plane spacing of the crystal. The right side of the above equation is obtained by deforming ε _hkl using an X-ray diffraction angle, and when measuring the crystal structure of a metal material or the like, it is common to find the stress using the right side of the above equation (Kanehara Jun, Applied Physics, Vol. 30, p. 496, edited by The Society of Materials Science, Japan, X-ray stress measurement standard, p. Since the crystal within the molded article after sealing with the epoxy resin composition often has a reduced crystal plane spacing, Δθ and stress take negative values, indicating that a compressive stress is applied. Examples of the type of the semiconductor device as a molded product include, but are not limited to, QFP, TQFP, and BGA. Note that a thinner semiconductor device has a thinner sealing layer and is easier to transmit X-rays.
When the diffracted light is detected, the diffraction intensity is increased, which is advantageous for the measurement. Examples of the present invention will be described below, but the present invention is not limited to these examples. Example 160 A piece obtained by cutting a silicon wafer (single crystal) into a 7 mm square through a silver paste on a copper frame for 160 pLQFP was mounted, and then a mold temperature of 175 ° C. and an injection pressure using the following epoxy resin composition were used. Molding and sealing were performed at 95 Kg / cm ^{2 for} a curing time of 120 seconds to obtain a molded product. Mo line (X
Line type) to irradiate the one before and after sealing, measure the diffraction angle,
The internal stress was calculated based on the above equation. In order to confirm reproducibility, the test was performed using five molded articles. The used silicon wafer had a Young's modulus of 2.04 × 10 ⁶ Kg / cm ² and a Poisson's ratio of 0.26. Table 1 shows the results. Spherical fused silica (amorphous) 825 parts by weight Biphenyl type epoxy resin (YX4000H, manufactured by Japan Epoxy Resin Co., Ltd., melting point 105 ° C., epoxy equivalent 195) 78 parts by weight Phenol aralkyl resin (Mitsui Chemicals, Inc. XLC) -LL, softening point 79 ° C, hydroxyl equivalent 175) 70 parts by weight 1,8-diazabicyclo (5,4,0) undecene-7 (hereinafter referred to as DBU) 2 parts by weight Carnauba wax 2 parts by weight Carbon black 3 parts by weight [ Comparative Example A stress was measured using a piezoelectric element. A 3 mm square piezoelectric element was mounted on a copper frame for 160 pL QFP via a silver paste, and the resistance of the piezoelectric element in the direction along the crystal direction and the resistance in the direction perpendicular to the crystal direction were measured.
Thereafter, the piezoelectric element was electrically connected to the copper frame by gold wire bonding from a wiring point on the surface of the piezoelectric element. Next, using the epoxy resin composition, a mold temperature of 175 ° C., an injection pressure of 95 kg / cm ² , and a curing time of 1
Molding and sealing were performed for 20 seconds to obtain a molded product. The crystal longitudinal and lateral resistances of the piezoelectric element were measured from the wiring on the copper frame of the molded article, and the internal stress acting on the piezoelectric element was determined from the change in the resistance of the piezoelectric element before and after sealing. In order to confirm reproducibility, the test was performed using five molded articles. Table 1 shows the results. [Table 1] In the example, it can be seen that the value of the internal stress hardly varies, and the internal stress can be accurately measured.
In the comparative example, when the value of the internal stress varies greatly and the resistance value after sealing is infinite, it is estimated that the gold wire connecting the copper frame and the piezoelectric element was cut during the injection molding. According to the present invention, the internal stress caused by the epoxy resin composition acting on the crystal in the molded article can be accurately measured, and the result is analyzed to solve the problems caused by the epoxy resin composition. Can help resolve the point.

Claims (1)

Claims: 1. A method for measuring an internal stress of a molded product obtained by sealing a crystal using an epoxy resin composition containing no inorganic filler having a crystal structure, wherein the X-ray is sealed. A method for measuring internal stress, comprising calculating an internal stress acting on a crystal in a molded article from a difference in diffraction angle obtained by irradiating the crystal before and after stopping.