RU2525684C1 - Method to assemble microelectromechanical devices - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method includes formation of volume current leads (VCL) on contact sites of a primary converter (PC) of crystalline type by the method of thermosonic microwelding with subsequent installation of the PC onto the board of the secondary converter of microelectromechanical devices and systems (MEMS). At the same time they previously perform high-temperature assembly of the PC made of a sensitive element SE and other functional elements of MEMS, which is carried out at temperature of not more than 500°C, afterwards to volume current leads made on contact sites of the PC, made of alternating metal layers Cr - Au with thickness of not more than 0.4 mcm, current leads are welded, in the form of a wire of gold by the method of contact welding. Then the PC produced in the specified manner is connected by the produced current leads in the form of a wire by the method of contact welding to contact sites of the secondary converter (SC) of MEMS.

EFFECT: increased reliability of functioning under conditions of high complex external impact.

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Description

The present invention relates to the field of microelectronics, and in particular to methods for assembling microelectromechanical devices and systems (MEMS) based on piezoelectric quartz.

In the art there is a problem of the reliability of MEMS operation, caused by the limitation of the magnitude of external (shock, energy and other) influencing factors.

As the basic methods of MEMS assembly, microelectronic technological methods are used, based on electrical connections using microwelding or soldering methods.

Known as a prototype is a method of assembling hybrid microassemblies, including mounting crystals, which is a primary converter (PP) on a hybrid microassembly board that serves as a secondary converter (VP), and before installation, crystals (PP) are formed by thermal compression welding on contact pads (KP) (club-shaped) conclusions (OM) soldered to pre-tinned KP hybrid microassemblies (VP) (AS No. 1496565, IPC H01L 21/50, publ. 08.10.1987).

The disadvantages of this method include the insufficiently high thermal conductivity of the assembly, the presence of soldered joints, which are susceptible to degradation under external high-energy influences in which MEMS is used, the limitation of the maintainability of assemblies, the low level of integration of MEMS elements, limited by the properties of soldered joints.

The task of the inventors is to develop a MEMS assembly method that provides high reliability of the operation of MEMS in conditions of high complex external influences.

The technical result of the invention is to increase the reliability of MEMS due to the guaranteed installation based on the reliable electrical connection of all KP elements of MEMS based on piezoelectric quartz and to increase the maintainability of MEMS.

The specified task and the new technical result are ensured by the fact that in the known MEMS assembly method, comprising performing on the contact pads of the primary transducer (PP) of the crystalline type of volumetric current outputs (S) by the method of thermosonic microwelding with subsequent installation of the PP on the secondary MEMS converter board, according to the invention, previously carry out a high-temperature assembly of a PP consisting of a sensitive element of the CE and other functional elements of MEMS based on piezoelectric of quartz, which is carried out at a temperature of not more than 500 ° C, after which current leads in the form of a gold wire are welded to volumetric current leads (S) made on contact pads made of alternating Cr - Au layers with a thickness of not more than 0.4 μm contact welding, then the PP obtained in this way is connected by formed current leads in the form of a wire by the contact welding method to the contact pads of the MEMS secondary converter (VP).

The proposed method for assembling MEMS is as follows.

In Fig.1 shows a view of the CP device PP with the formed system OB, where 1 - volumetric conclusions of a spherical shape.

In Fig.2 shows a General view of the Assembly MEMS, where 1 is the primary Converter (PP); 2 - secondary converter (VP); 3 - contact pad (KP) of the sensitive element (SE) PP; 4 - volumetric findings (S) of a spherical shape; 5 - wire leads made of gold; 6 - contact pad (KP) VP.

Prior to assembling MEMS on a CP of a fabricated quartz CE PP having a given design and topology with deposited alternating Cr - Au metal layers with a thickness of not more than 0.4 μm, an OM is formed from a gold wire.

The wire emerging from the capillary of the ultrasonic welding unit is melted using an electric discharge to produce a ball that is welded to the quartz PP core. The wire comes off at the base of the OM. As a result, a golden sphere of a spherical shape is obtained at the control point.

CEs with a formed system of spherical-shaped current leads are collected in PP under conditions of high-temperature processing at a temperature of about 500 ° C. This operation leads to a change in the composition of the KP, namely, after assembly in the composition of the KP PP, there is an increase in the relative mass content of oxygen in the composition of the gold film, diffusion of chromium into the gold film, which lead to a deterioration or complete absence of welding of wire leads on the KP PP. In order to avoid the manifestation of these negative factors, the formation of organic matter is foreseen prior to the assembly process of the measuring unit of the PP.

After the high-temperature assembly, in the zones of the control unit (Fig. 2, position 3), the formed spherical OBs (Fig. 2, position 4) are subjected to resistance welding with gold wire leads (Fig. 2, position 5). The PP block assembled in such a way is connected by welded wire current leads by contact welding to the VP VP (Fig. 2, position 6).

The sequence of operations during the assembly of MEMS according to the proposed method is as follows:

1. Chemical treatment of quartz PP.

2. The formation of a spherical shape of gold from the method of thermosonic welding at the quartz CHE PP.

3. Assembly of PP at a temperature of 500 ° C.

4. Resistance welding of gold wire leads to formed OM.

5. Connection by contact welding of wire current leads made of gold with KP VP.

The formation of organic matter prior to the assembly of the PP block allows locally, selectively, with high adhesive strength at the desired point on the KP PP to increase the gold thickness without changing the electrical parameters of the PP, and minimize the increase in the relative mass content of Wt% oxygen and the diffusion of chromium into the gold film, which lead to reduce the reliability of the welded joint of PP with VP as part of MEMS.

Thus, the use of the proposed method improves the reliability of MEMS by ensuring a guaranteed connection of all the contact pads of MEMS elements due to the replacement of traditional soldering by microwelding and to increase their maintainability and a high level of integration of MEMS elements.

Example 1. On a batch of CE 1111 in the amount of 6 pcs. 60 welded joints (10 welded joints each) were carried out at the ultrasonic welding unit US.IMM-5. The welding process begins with the formation of a ball of gold wire of the grade cr.Zl.99.99-0.04T. The gold wire is directed vertically through the welding tool into the welding area to implement the thermosonic micro-welding method. The end of the wire (the axis of the output is perpendicular to the plane of the KP) is preliminarily fused using an electric spark generator, forming a ball. Then the welding tool descends to the surface of the KP CHE PP. The ball is deformed under pressure and takes the form of a hemisphere. In this case, the lower surface of the ball forms a welded joint with the material KP PP. The relative deformation of the ball during the formation of high-quality compounds is 50-60%. Heat is brought into the welding zone by heating the working tool to a predetermined temperature (about 100-120 ° C), which is experimentally shown to improve the quality of welding.

In order to form a spherical-shaped OM, the values of the parameters of thermosonic welding are set in such a way that, after the formation of the OM and the welding process, the wire is detached at a predetermined location (in the zone of connection of the ball with the wire). The diameter of the formed OM is 2-3 diameters of the gold wire. At each KP, SEs form what is needed to connect with the available number of MEMS elements (in this case, -5) OM. The assembly of PP is carried out, consisting of SE and functional or structural elements based on piezoelectric quartz at a temperature of 500 ° C.

On OV current leads from a gold wire of red. Zl.99,99-0,04T contact welding are welded. Welding modes are selected based on the conditions for obtaining maximum strength of welded joints. Golden wire current leads are welded by contact welding to the VP gearbox. This method of assembly provides the opportunity, if necessary, to replace a failed PCB, to repair MEMS by breaking current leads from the PCB and replace it without damaging the MEMS, which is not provided for in the prototype.

The use of this assembly method increased the reliability of MEMS operation due to the guaranteed installation based on a reliable electrical connection of gas-mains based on piezoelectric quartz assembled from functional elements at a temperature of not more than 500 ° C with VP using microwelding methods and increased the maintainability of MEMS.

Claims (1)

A method of assembling microelectromechanical devices (MEMS), including performing on the contact pads of the primary transducer (PP) of the crystalline type of volumetric current leads (S) by the method of thermosonic microwelding, followed by installing the PP on the board of the secondary MEMS converter, characterized in that the high-temperature PP is preliminarily assembled, which consists of a sensitive element (SE) and other MEMS functional elements based on piezoelectric quartz, which is carried out at a temperature of not more than 500 ° C, after that, to the volumetric current leads (RV) made on the contact pads made of alternating Cr - Au layers with a thickness of not more than 0.4 μm, the current leads in the form of gold wire are welded by contact welding, then the resulting PP in this way is connected to the formed current leads in the form wire method of contact welding to the contact pads of the secondary transducer (VP) MEMS.

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