RU2349025C1 - Production method of minuature quartz generator (resonator)-thermostat - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrical engineering and may be used for the production of highly stable quartz resonators and generators with inner thermostating. The production method provides for installing radio elements of generator (resonator) and quartz piezo-element by their group soldering to the board. The board is then installed to the housing basis. After that, the generator (resonator) is heated at 150°C and tuned to the operating frequency under vacuum conditions. The housing lid is vacuum tightly connected with the basis. The thermovacuum annealing of generator (resonator) at 150÷200°C is performed at the open riveted hole in the housing lid. Then, the generator is cooled to the confinement temperature (70±10) °C. The housing is vacuum confined by riveted hole soldering in the lid. After installation, the board with soldered radio elements and the housing lid with the soldered riveted hole are subject to vacuum annealing during 0.5÷2.5 hours at the temperature of solder melting (T_h÷T_l), where T_h and T_l - high and low temperature of solder melting. The thermovacuum annealing of generator (resonator) at the open riveted hole is conducted until the surface inside the generator (resonator) housing is cleaned to 6·10^-5÷2.5·10^-2 tore·sm³/f·m² which is defined by the specific gas release value within the temperature 120-180°C.

EFFECT: improved efficiency, high items quality and reliability.

2 dwg, 1 tbl

Description

The invention relates to a frequency stabilization technique and can be used in the production of highly stable quartz resonators and oscillators with internal temperature control.

The known technology of piezoelectric and acoustoelectronic devices, in particular quartz thermostatically controlled oscillators and resonators [1, 2]. The technology includes mounting by soldering, spot welding or gluing the radio elements of the circuit onto the board, mounting the board onto the base of a glass or metal case, preliminary annealing in vacuum, vacuum frequency tuning, thermal vacuum annealing at temperatures of 150-200 ° C and vacuum sealing by solder connection of the case or electric contact welding . This technology requires long-term (up to 16 hours) thermal vacuum annealing to ensure high stability of miniature products. In addition, additional degassing using internal getters is used to maintain a 10 ^-4 torr vacuum during continuous operation.

The closest analogue is the manufacturing process for serial production of thermostated quartz resonators [3].

The process includes assembling resonator-thermostats by gluing discrete elements and soldering a piezoelectric element to the holder with ПСрО 10-90 solder (220 ° С), preliminary and final frequency tuning, thermal vacuum annealing for 5 hours at a temperature of 150 ° С and a pressure of 2 · 10 ^-5 torr , cooling to a temperature of (70 ± 10) ° С, activation of the getter inside the housing and soldering of the resonator thermostat from the comb. Here, vacuum technology with getter activation ensures long-term reliability and product quality, but is unsuitable for the productive production of miniature quartz oscillators (resonators) -thermostats. Also, more shifts are required for thermal vacuum annealing of products to ensure the stability of their parameters.

The technical solution proposes a technology for manufacturing a miniature quartz oscillator (resonator) with internal temperature control in a metal-glass case. The objective of the invention is to increase productivity, ensuring high quality and reliability of the product by eliminating the influence of internal gas evolution on the parameters of the product in operation during long-term (10-15 years) operation.

The problem is solved in that in a method for manufacturing a miniature quartz oscillator (resonator) of a thermostat, including mounting radio elements of a generator (resonator) circuit and a quartz piezoelectric element on a circuit board, mounting the circuit board on the housing base, annealing the generator (resonator) in vacuum at a temperature of 150 ° C during the shift, the vacuum setting of the generator (resonator) to the operating frequency, the vacuum-tight connection of the housing cover with the base, for example, by electric contact welding along the circuit, thermal vacuum annealing of the generator (reason ora) in an oil-free environment at temperatures of 150 ÷ 200 ° C with an open bead hole in the housing cover, cooling to a sealing temperature of (70 ± 10) ° C and vacuum sealing of the case by sealing the bead hole in the cover, the circuit board after mounting the radio elements with group soldering and the case cover with a sealed bullet hole is subjected to vacuum annealing for 0.5 ÷ 2.5 hours at the melting temperatures of the solder (T _n ÷ T _in ), where T _n and T _in are the lower and upper melting points of the solder, and thermal vacuum annealing of the generator ( resonator) and the open bullet hole in the housing cover is carried out until the surface inside the generator (resonator) is cleaned 6 · 10 ^-5 ÷ 2.5 · 10 ^-2 l · torr / (s · m ² ), which is determined by the value of specific gas evolution in the temperature range 120 ÷ 180 ° C. The processes of deep thermal vacuum annealing, cooling to sealing temperatures and the sealing process are carried out in a single vacuum cycle.

In this technical solution, it was possible to provide a 10 ^-4 torr vacuum during long-term operation of the products in thermostatting modes from 60 to 85 ° C without the use of getters (getters) inside the cases.

Figure 1 shows data on the heat loss of products through vacuum insulation at various rarefactions in the housing and the temperature of the housing 25 ° C.

Figure 2 shows the temperature dependence of the rate of internal gas evolution (B1, B2, B3, B4) and internal gas absorption (P3, P4) in the product bodies.

A method of manufacturing a miniature quartz oscillator thermostat (KGT) or quartz resonator thermostat (KRT) is implemented in this sequence. On dielectric microcircuits (polycor, BeO) with tinned contact pads, for example, POS-61 solder in a group soldering installation, radio elements of the KGT or KRT circuit, such as resistors, temperature sensors, capacitors, etc. are mounted. Then, with the same solder, nickel piezoelectric element (PE) holders are mounted on the microboards. At the same time, the bunching holes in the covers of TO-8 or DIP-14 metal-glass cases are sealed by a group method. Prepared microassemblies and housing covers are placed in a chamber of a Rogun type vacuum furnace and vacuum annealed for 0.5–2.5 hours at melting temperatures of solder Т _н ÷ Т _в , for example, 183-212 ° С for POS-61M. After cooling to room temperature, quartz PEs are mounted on the boards, strengthening them to the holders with TOK-2 type electrically conductive adhesive; and complete the installation of products by gluing the boards on the base of the cases with standard K-400 glue through glass insulator racks. Next, the generators or SRT are annealed in vacuum at a temperature of 150 ° C for a shift (8 h), providing structural shrinkage of the elements at the gluing sites, and after measuring the frequency using standard methods, the operating frequency is set by spraying gold onto PE electrodes in a specialized vacuum installation. When setting the frequency in a vacuum, the generator is turned on and thermostating is brought into operation; Gold from the evaporator is deposited through the diaphragm on the PE electrode. At the next stage of the process, they make a vacuum-tight connection of the covers with the bases of the cases on which the generators are assembled, as a rule, by electric contact welding along the contour. The bell-shaped openings of the housings are opened and the products are transferred to the finishing operations for deep thermal vacuum annealing, cooling to sealing temperatures, and sealing by sealing with the bell-shaped holes in the housing lid in the oil-free vacuum chamber of the upgraded Alfa-N installation. If necessary, a selective control is carried out on the cleanliness of the surface inside the housing of the finished products, determining the specific gas evolution for the selected temperature in the range of 120-180 ° C.

The proposed technical solution was developed using the "probe method", which allows you to measure the degree of evacuation and tightness of products in metal-glass cases for a wide range of pressures and temperatures. A microplate is glued to the base of the body through the rack-insulators, on which the electric heater and temperature sensor are placed in the given geometry. After evacuation and sealing of the case (TO-8 or DIP-14), such a probe simulates thermal processes in a CMT or in a thermostatically controlled crystal oscillator. By stabilizing the temperature of the board inside the case, you can measure the power consumed by the probe for various experimental modes.

In Fig. 1, “triangles” indicate the data of measurements of heat loss through vacuum insulation, W = W _p -W ₀ , for probes in these cases at a temperature of the circuit board of 80 ° C, and the case temperature of 25 ° C, and vacuum from 5 · 10 ^-5 torus up to 2 · 10 ^-2 torus, where W _p is the total power consumed by the probe at a selected pressure P; W ₀ is the total power (heat loss) consumed by the probe in high vacuum, usually at a pressure of ≤5 · 10 ^-5 torr.

So built the average dependence of ABC in figure 1. For SRT in the TO-8 package and KGT in the DIP-14 package, a similar DEF dependence is obtained in FIG. 1, the measurement results are indicated by “squares”. Moreover, the measurements for the resonators were made at an extremum temperature of quartz PE of 80 ° C, and for generators - the same at a temperature of 60 ° C. On the same scale of the values of W and P, the sections AB and BC in Fig. 1 are linear, then the rate of change of heat loss (W) from pressure (P) will be tg β; or tgβ = ΔW / ΔP. According to our measurements, the average value of tgβ for probes in the pressure range from 10 ⁻⁵ torr to 10 ⁻² torr is 1.2 · 10 ³ mW / torr. For SRT and QGT, the tgβ value is somewhat larger and equals 1.7 · 10 ³ mW / torr. This is due to the fact that, in addition to the microplate with radio elements, piezoelectric elements are installed in the products, which are comparable in size to the board. Probably, a change in the geometry of vacuum insulation significantly affects the re-emission of energy.

The obtained calibration graphs in figure 1 are used to measure the rates of gas evolution and gas absorption in probes and in prototypes of products, as well as to determine the boundary values by the distinguishing features of the invention.

The gas filling rate of a closed volume V in conventional terminology means the change in pressure ΔP in this volume over time t:

Substitute the already found value

then

When using an electric heater, W = I · U, where I and U are the current and voltage in the heating circuit. Measuring the initial I _n , U _n and final I _k , U _k values for the selected time t, we obtain a working expression for determining the speed

Typically, SRT and KGT operate at a constant voltage, then

The devices are highly stable in all respects, therefore, at a fixed temperature of measurements of the rate of gas evolution (absorption), the sensitivity reaches a value of 10 ^-10 torr · cm ³ / s.

The prototypes of the generators (10 pcs.) And resonators (40 pcs.) Were made at a frequency of 10 MHz according to the specified process technology. Next, the level of residual vacuum in the body of the products was measured using calibration graphs in figure 1. And then, by the considered method, the rates of gas evolution (desorption) and gas absorption (adsorption) inside the body of the product were measured in the temperature range from 20 to 220 ° C. Only microplates inside the probes were heated to temperatures above 180 ° C. KGT and KRT were kept at the selected temperature in a muffle furnace. As a rule, at first, prototypes were investigated for gas evolution, while the heating temperature was raised stepwise from 60 to 220 ° C. Then these same samples were studied with a stepwise decrease in temperature from 100 to 20 ° C.

Figure 2 shows the most probable rates of gas evolution (absorption) in experimental samples and probes with variations of the process:

B1 - thermo-vacuum finish annealing at a temperature of 150 ° C for 8 hours without preliminary degassing of solder on the contact pads of the board and the puklevka;

B2 - the same at a temperature of 175 ° C;

B3, P3 - the same at a temperature of 175 ° C for 8 hours, but the boards with the solder pads and the covers of the housings with pickles were subjected to vacuum annealing at melting temperatures from 0.5 to 2.5 hours;

B4, P4 - the same for probes, in which the boards had contact pads that were not tinned with solder.

Table 1 Conditions Output parameters The increase in heat loss, mW Residual vacuum, torus Yield,% 1. Sealing of beetle in vacuum without preliminary vacuum annealing of solder 2 ÷ 18 10 ^-4 ÷ 10 ^-2 0-10 2. The same after annealing of the contact pads on the board and in the bead at a temperature of 185 ° C for 2.5 hours 0 ÷ 3 10 ^-5 ÷ 10 ^-4 ≥90 3. The same at 215 ° C for 0.5 h 0 ÷ 2 10 ^-5 ÷ 10 ^-4 ≥90 4. The same for probes without solder on the board. 0 ÷ 2 10 ^-5 ÷ 10 ^-4 up to 100

Separately, the influence of the sealing operation of a bead-hole in vacuum on the output parameters of the product was investigated. The data are given in the table. Products with a residual vacuum of better than 10 torr were recognized as suitable, in which no internal gas evolution was detected during an exposure of 24 hours in the operating mode.

Analysis of the data in figure 2 shows that the conditions for graphs B1 and B2 do not provide a solution to the problem. Firstly, the yield of suitable products does not exceed 10%, see table. Secondly, the assessment of vacuum in products after 10 years of operation gives values of 6.4 · 10 ^-1 torr (point G) and 6.4 · 10 ^-4 torr (point H). The calculation is carried out according to the formula

for SRT in the TO-8 case with a volume of 0.5 cm ³ . According to [1, 2], long-term frequency stability cannot be guaranteed.

It was established that the task is solved under technological conditions that provide deep degassing of products within the boundaries of KLMN (shaded) according to graphs B3 and B4. However, such modes have a large number of parameters: temperature, degree of vacuum during annealing, time of heating, holding and cooling, gas exchange rate, etc. In addition, these boundaries are due to the design differences of products, such as volume, area, size of the beak hole, the range of radio components, the number of adhesives and solders. Therefore, it is convenient to choose a generalized parameter characterizing the degree of purity of the surface sorbing gas. This parameter is the specific gas evolution [4, 5], in other words, the amount of gas emitted (absorbed) from the geometric area of the sorbed surface per unit time. According to figure 2, it is obvious that with a specific gas evolution equal to or less than the initial values of the gas evolution velocity in the LM section, the conditions of the task are provided. Given the geometry of the miniature products at the point L, the specific gas evolution is 6 · 10 ^-5 torr · cm ³ / (s · m ² ), and at the point M - 2.5 · 10 ^-2 torr · cm ³ / (s · m ² ) respectively. In practice, it is necessary to measure, for example, with selective control of the rate of internal gas evolution in the temperature range 120-180 ° C and divide by the geometric area of the products. On graphs B3 and B4 it can be seen that the limit of 120-180 ° C on the left is limited by the “threshold” of unstable gas exchange, and on the right by the lower boundary of melting of solder.

Thus, the distinguishing feature of the claims is chosen: thermal vacuum annealing of the generator (resonator) with an open bullet hole in the housing cover is carried out until the surface is clean inside the generator (resonator) housing 6 · 10 ^-5 ÷ 2.5 · 10 ^-2 tor-cm ³ / (s · m ² ), which is determined by the value of specific gas in the temperature range 120-180 ° C.

Another feature that meets the solution of the problem is selected by the output parameters of the table. The yield of piezoelectric products exceeds 90% after vacuum annealing of boards with solder pads at the places of installation of radio elements by group soldering and housing covers with a sealed bead hole for 0.5 ÷ 2.5 hours at solder melting temperatures T _n ÷ T _c . The boundary values of the annealing time were obtained experimentally and are in good agreement with the results of graphs B2 and B3 in figure 2. Indeed, over 2.5 hours at 183 ° C, the total gas evolution in the test samples is comparable to the gas evolution at 220 ° C in 0.5 hours. Within such parameter limits, we obtain surfaces of the same purity with respect to specific gas evolution.

Information sources

1. Reference. Piezoelectric resonators. Under. ed. P.E. Kandyba and P.G. Pozdnyakova. M .: Radio and communications, 1992, p. 318-382.

2. Mostyaev V.A., Dyuzhikov V.I. Technology of piezoelectric and acoustoelectronic devices. - M .: Jaguar, 1993, p. 163-174, 185-199, 223-257.

3. The technological process of manufacturing a quartz resonator-thermostat TsLZ.380.059, Research Institute of Instrument Engineering, 08.19.92., Omsk.

4. Danilin B.S. and Minaichev V.E. Fundamentals of designing vacuum systems. - M .: Energy, 1971, p. 5-10, 353.

5. Groshkovsky J. Technique of high vacuum. - M .: Mir, 1975, p.135-167.

Claims (1)

A method of manufacturing a miniature quartz oscillator (resonator) of a thermostat, including group soldering of radio elements of a generator (resonator) circuit and a quartz piezoelectric element on a circuit board, mounting the circuit board on the housing base, annealing the generator in vacuum at a temperature of 150 ° C, setting the generator (resonator) to the operating frequency in vacuum, vacuum-tight connection of the housing cover with the base, for example, by electric contact welding along the circuit, thermal vacuum annealing of the generator (resonator) at temperatures of 150-200 ° С with open th hole in the housing cover, cooling to a sealing temperature of (70 ± 10) ° С and vacuum sealing of the housing by sealing the bead hole in the cover, characterized in that the board after mounting the radio elements in groups and the housing cover with a sealed bead hole are vacuum annealed in within 0.5 ÷ 2.5 hours at the melting temperature of the solder (T _n ÷ _T), where T _n and T _{in the} - lower and upper solder melting temperature, and anneal thermovacuum oscillator (resonator) puklevochnom at opening hole in the lid body wasp estvlyayut to surface cleanliness inside the generator housing (cavity) 6 × 10 ^-5 ÷ 2,5 · 10 ^-2 Torr · cm ³ / (s · m ^2), which is defined by the specific value of outgassing in the temperature range 120-180 ° C.

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