SU1697991A1 - Method of laser soldering of semiconductor device lead to a metallized dielectric substrate - Google Patents

Abstract

The invention relates to soldering, in particular, to methods of laser soldering the output of a semiconductor device to a metallized dielectric base. The purpose of the invention is to improve the quality and strength of the solder joint. In the output of a semiconductor device, a groove is created in the form of a groove, the width of which at the base is equal to the diameter of the laser beam. to a + 55 °, where a is the angle of convergence of the laser beam. The wall thickness of the bottom of the groove is chosen in the range of 1 / 4- - 1/3 of the output diameter. The thickness of the top layer of the dielectric base should be at least 12 microns, and the pulse duration laser radiation should be at least 2.5 ms. The soldering method increases the percentage of yield of products, increases labor productivity by reducing the heating time of the soldering zone. 1 table, 2 sludge

Description

The invention relates to soldering, in particular k, a method of laser soldering the output of a semiconductor device to a dielectric metallized base.

The aim of the invention is to improve the quality and strength of the solder joint.

The laser soldering of the output of a semiconductor device to a metallized dielectric base is carried out by a defocused laser beam, by creating a groove in the output of the semiconductor device in the form of a groove whose width at the base is equal to the diameter of the laser beam directed into the recess. The angle between the edges of the groove bevel is chosen in the range from a + 35 to a + 55 °, where a is the angle of convergence of the laser beam, the wall thickness of the bottom of the groove is chosen in the range of 1/4 - 1/3 of the output diameter, and the thickness of the upper layer is soldered metallization of the dielectric base is not less than 12 microns, and the laser pulse duration is not less than 2.5 ms.

Depending on the length of the weld seam, the diameter of the defocused laser beam, and the pitch of the location of the heating spot of the output, the heating of the output is carried out at several points where the laser beam is directed.

The number of points for the formation of a solder joint is determined from the ratio

п к4--1. but

where n is the number of points, pieces

I is the length of the foot weld, mm,

d is the diameter of the defocused laser beam, mm;

h h

H

K - coefficient of movement of the heating zones.

The selected wall thickness of the bottom of the groove in the output ensures the stabilization of the process of laser soldering. In the case of an increase in the wall thickness of the bottom of the groove beyond 1/3 of the diameter of the outlet, a large expenditure of energy of the laser beam is required for soldering. Reducing the wall thickness to less than 1/4 of the output diameter leads to instability of the soldering process. The thickness of the solder layer covering the base plating is at least 12 microns required to obtain good soldering of the joint.

The pulse duration of the laser beam is at least 2.5 ms, determined by the sufficient heating time of the output materials and the metallization of the dielectric base for melting and spreading the solder and filling the gaps with solder. The results of laser soldering of the output, which has various structural characteristics of the groove, with a certain thickness of the coating and the magnitude of the pulse duration, radiation and strength characteristics of the connection are presented in the table.

Example. Whether the laser beam soldered a copper lead of a semiconducting device with metallized dielectric bases. The diameter of the copper output was 400 µm, and the metallized base was a 500 µm thick metallic substrate, on which the following metallizations were deposited in the following sequence: a chromium layer 500 A thick provides adhesion of the subsequent metallized layers to the base; a copper layer with a thickness of 8 microns, performing the function of an electrical conductor, a layer of nickel (2 microns) providing protection of the copper layer against oxidation and corrosion. The final layer was solder 12 microns thick. This layer provides solder joints. A tin-bismuth alloy was chosen as a solder.

The copper output was preformed and had the following structural dimensions:

groove width (b) 0.5 mm; bottom groove thickness (5i) 100 microns; the thickness of the layer is solder from an alloy of tin-bismuth (d) 12 μm;

the bevel angle of the edges of the groove output (a) 60 °; the length of the foot weld (I) is 1.5 mm; the diameter of the copper lead (da) is 0.4 mm, the step ratio of the solder joint (K) is 1.0.

The number of points for the formation of a paired compound was determined by the formula:

- 1 2 points

n K-i - 1 1,

To obtain comparative data, a copper laser beam was soldered to the metallization of the dielectric base with a laser beam. The output had various structural dimensions: b, d-, a.

FIG. 1 shows the connection of the output of a semiconductor device with a metallized dielectric plate; in fig. 2 is a section A-A in FIG. one.

A semiconductor device manufactured using laser soldering is shown in FIG. 1, where the laser diode 1 is mounted on a copper plate 2, attached to the metallized sitall substrate 3 with conductors 4. A copper lead 5, having a groove of length I, is soldered to the plate 3, which is a metallized dielectric base. Places of direct contact of the laser beam with the bottom of the groove are indicated by the position 7.

FIG. 2 shows a laser beam 6, heating the bottom of the groove of width b, the angle of convergence of the laser beam a, and the angle between the edges of the bevel of the groove is 1 1 a + (35 - 55 °), the wall thickness of the bottom of the groove 5i alloy tin - bismuth $ 2.

When choosing the soldering mode and the structural characteristics of the groove for soldering with a certain strength and quality of the joint, you should follow the table.

The use of the invention allows to increase the percentage of yield of products, labor productivity by reducing the time of heating of the soldering zone, in addition, allows you to create semiconductor devices that allow high current loads.

Claims (1)

Invention Formula A method of laser soldering of a semiconductor device output to a metallized dielectric base, according to which the output is placed on a layer of solder deposited on the surface of metallization, and the soldering is carried out with a defocused laser beam, characterized in that, in order to improve the quality and strength of the solder joint, To the output, a groove is made in the form of a groove, the width of which at the base is equal to the diameter of the laser beam directed into the groove; the angle between the edges of the groove of the groove is chosen in the range from a + 35 ° to a + +55, where a is the angle of convergence of the laser beam, the wall thickness of the bottom of the groove is chosen in the range of 1 / 4-1 / 3 of the output diameter, and the thickness of the solder layer on the metallized dielectric base is at least 12 µm, and the pulse duration of the laser radiation is at least 2, 5 ms Note. During the experiments, the following values were taken: laser beam diameter 0.5 m; the impact of the laser beam occurred at the bottom of the trapezoidal groove; the coefficient K was chosen equal to 1.0 of the ratio of the diameter of the beam to the distance between the points of illumination of the beam; radiation energy density was unchanged 1 Aa FIG. 2