SU743815A1 - Method of hypersonic microwelding and soldering - Google Patents

Description

one

The invention relates to electronic engineering and can be used in the design of high-performance and efficient electro-acoustic devices for micro-welding and soldering, for example when assembling semiconductor devices and integrated circuits.

The known method of hypersonic welding and soldering by imposing static pressure on the connected elements 1.

However, the excitation of Lamb waves on the substrate with the condition of observing the location of the antinode of the standing wave in the middle of the welding zone is associated with certain difficulties, since this requires the condition where K is the Lamb wavelength in the substrate, d is the thickness of the substrate. This condition is especially difficult to handle when working in the range of hypersonic frequencies, where the wavelength is small. In addition, the resonant method of excitation of acoustic waves for micro-welding has a significant drawback: the process of connecting elements during micro-welding leads to a disturbance of the resonant mode. At the same time, the parameters of the micro-welding process change, which leads to a decrease in process stability and a decrease in the quality of the micro-welded joints.

The purpose of the invention is to improve the quality and reliability of micro-welded joints.

This goal is achieved by the fact that, in the zone of the connection of the coptable elements, surface acoustic waves of ultrasonic and gyrosonic frequencies are excited, the length of which does not exceed the total thickness of the connected elements. In order to improve the quality of the micro-welded joints, various combinations of the Relé, Lamb, La Wa, Sesava and Stonley acoustic waves or the Gouluba-Blustein electroacoustic waves are excited in the joint zone.

15 In FIG. 1 is a diagram illustrating the proposed method with a piezoelectric crystal; in fig. 2 - the same, with a microwave resonator. The diagrams contain pin 1, substrate 2,

20 aluminum film 3, piezoelectric crystal 4, piezoelectric film 5, metal electrodes 6, generator 7, microwave resonator 8, ferromagnetic film 9, waveguide 10 and communication hole 11.

25 The excitation of surface acoustic waves of hypersonic frequencies in the zone of attachment of pin 1, naimer, to aluminum film 3 on substrate 2, is produced using a piezoelectric epitaxial transducer, representing

is a thin layer of a piezoelectric crystalline substance with high resistance, formed on conductive substrate 2. The upptax converter can be a converter in the form of a single single crystal of conducting cadmium sulfide with a high-resistance cadmium sulfide film formed on it. 1U1 metal electrodes b are used to connect the excitation electric voltage from the generator output to the transducer. When electrical oscillations of a hypersonic frequency are applied to the transducer, the main part of the voltage drop occurs on the film b with high resistance. The mechanical stress, proportional to the intensity of the electric field, will be maximum inside the film 5. Thus, the film b will excite acoustic waves. Performing it fairly thin (several microns) and exciting the shear-wave resonant mode, surface waves of hypersonic frequency are obtained in the zone where the output i connects to the substrate 2.

The considered transducer is rather wideband and is used in imitation of surface acoustic waves of the noise frequency spectrum.

The following combinations of types of surface acoustic waves in connected elements are possible.

The waves of Rele, Lamb and their combination in both connected elements or in one of them. This case is possible when the mutual overlapping of the elements is comparable with the wavelength. The Rayle and JiSMOa waves will also propagate in that part of the connected elements where these elements do not overlap with each other. By ipH honoring the will of Rayle in the element, the wavelength should be much less than the thickness of this element, the latter being considered as a semi-infinite solid. When Lamb waves are excited, the wavelength should be commensurate with the THICKNESS of the element, in this case, the connected element can be considered as a plastic.

The combination of the waves of Rele, Lamb, Lwa and Sesava in the junction zone. This case is possible when the output thickness is commensurate with the wavelength, and the thickness of the substrate and the mutual overlap of the output with the substrate are much greater than the wavelength. In this case, the elements to be joined can be considered as a layered medium in which waves similar to waves 1 W, as well as Lamb waves can propagate. The waves of the symmetric type are similar in this case to the Rayle waves, and the waves of the antisymmetric type are the Sesawa waves,

The excitation of stonley waves in the junction zone. This case is possible when the thickness of the connected elements and their mutual overlap along the contact zone

much longer wavelength.

Electroacoustic Gul Bubblestone waves in the junction zone. This case is possible when the material of at least one of the connected elements, and, for example, a substrate, is piezoelectric.

The advantages of surface acoustic waves of hypersonic frequencies are that they are intensively absorbed by the output and substrate material, and the absorption of hypersonic surface waves in metal, for example aluminum, occurs due to strong scattering at the boundaries of the crystallites. Oh

At each boundary of the crystallite, reflection and refraction of acoustic waves occur, which is caused by the anisotropy of the material. In addition, the surface waves of hypersonic frequencies are strongly absorbed

thermal phonons of the crista. lattice. The energy of the surface waves in this case is spent on the activation of a thin surface layer of the joining elements and intensifies the process of diffusion without significant external deformation of the jointed parts.

The excitation of surface acoustic waves of hypersonic frequencies is also possible with the help of other types of piezoelectric transducers on high-resistance layers, for example, with a diffusion or depleted layer. In the noise frequency spectrum, the use of an electroacoustic converter on

CdS diffusion layer with extended frequency band. The high resistance diffusion layer of this converter is formed by sputtering copper in vacuum on a CdS plastichku heated to several hundred

degrees

SNCH resonators with thin piezoelectric or magnetostricded diodes placed at the antinodes of their electric or magnetic field can also be used to excite hypersonic surface waves. The excitation of surface acoustic waves of hypersonic frequencies can be carried out using a rectangular microwave resonator 8 used in conjunction with a topfilm ferromagnetic transducer. In this case, a ferromagnetic film 5, which performs shear oscillations and excites surface acoustic waves of hypersonic frequency in the zone of connection of pin 1 with substrate 2, is placed on the side wall of the rectangular resonator 8, i.e. in the antinodes of the magnetic zero of the resonator. In this case, the magnetic field is oriented in the plane of the film 9. The film 9 is preliminarily magnetized by a strong magnetic field, usually directed perpendicular to its plane. When excited in the resonator 8 by means of the waveguide 10 through the communication hole 11 of the microwave field, oscillations of the magnetization excite deformation in the ferromagnetic film and surface acoustic waves propagate in the connected elements.

In this case, the relationship between the electrical parameters of the microwave resonator and the acoustic parameters of the magnetostriction transducer is determined by the expression

2a6

WITH.

a2 h

where AS is the length of the transverse waves in the transducer;

Cs is the speed of propagation of transverse waves in the film;

C is the speed of electromagnetic waves;

a, b are the length and width of the microwave resonator, respectively.

The resonator was tuned by changing one of the dimensions a or b.

The efficiency factor i of this electroacoustic converter is determined by the expression

S-C, -Q

TO

where K, is the magnetomechanical bond coefficient of the film;

5 - square film;

Q is the Q-factor of the microwave resonator;

ω is the circular frequency;

V - part of the cavity volume occupied by the film.

For example, when micro-welding the leads of an integrated circuit with petals of a non-perforated aluminum tape with a thickness of 30 µm using 20 MHz Rele waves, the quality of micro-welded compounds increases by 30-40%, the reproducibility of quality increases 1.5 times.

With the excitation of the Rele, LVA, and Sesawa waves with a frequency of 100 MHz, the quality of the welded joints is increased by 45-50%, and the reproducibility of the quality increases 1.4 times.

The use of acoustic waves with a frequency of 1 MHz allows to improve the quality of micro-welded compounds by 20-25%. The quality of the quality in this case

increases by 1.2 times.

The electroacoustic waves of the Gulva-Blusteppa are excited when they propagate surface-type waves of any type in connected elements, provided that at least one material of the connected elements, such as a nodlozhki, is a piezoelectric. Using the quality of a substrate as an arsennd of galli, on average, increases the quality of the compound by a factor of 1.2–2.0.

Form u lann 3 obretenn

Claims (3)

1. The hypersonic micro-welding and soldering method by applying static pressure on the connected elements, characterized in that, in order to improve the quality and reliability of the micro-welded joints, surface acoustic waves of ultrasonic and hyper-frequency frequencies are excited in the zone of contacting elements thickness of the connected elements. 2. Method of clause 1, characterized in that in the junction zone of the moons, various combinations of acoustic waves of Rele, La va, Lamb, Cesava and Stonley give. 3. The method according to claim 1, characterized in that, in the junction zone, the electroacoustic Gul Eva-Blustein waves. Sources of information taken in the internal examination the USSR 45 1. Copyright certificate № 502729, cl. In 23K 19/00, 1974.