JPH0693591B2 - Press-fit type airtight retainer for piezoelectric vibrator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a press-fit type airtight retainer for a piezoelectric vibrator, which prevents the airtightness and the characteristics of the piezoelectric vibrating element from being impaired.

B. SUMMARY OF THE INVENTION The present invention is a press-fit type airtight retainer for a piezoelectric vibrator, in which a cap is press-fitted onto a base to which a piezoelectric vibrating element is attached, and a lead or lead alloy is provided at least at a joint portion with the base on the inner surface of the cap. By forming a lead-based plating layer composed of, and further forming a silver plating layer on the surface of at least the lead-based plating layer, the piezoelectric vibrating element is formed such that the plating melts in the reflow furnace to cause poor airtightness or vapor. It prevents the adherence to the.

C. Conventional Technology An airtight retainer that hermetically seals a piezoelectric vibrating element is composed of a base that holds the piezoelectric vibrating element, and a cap that covers the piezoelectric vibrating element and the base.

As an airtight retainer, a press-fit type airtight retainer in which a seal between a base and a cap is formed by rubbing a soft metal plating layer is widely used at present. This press-fit type airtight retainer has a soft metal layer formed by plating on at least the inner surface of the cap at the joint surface between the base and the cap, and the airtightness inside the cap is maintained only by press-fitting the cap into the base. The following are press-fit type airtight retainers.

As shown in FIG. 4 (a), the piezoelectric vibrating element 3 is attached to the mounting portion provided at the inner end portions of the pair of leads 5 that are provided directly to the base 4 or through the base 4 while being hermetically penetrated while insulated. And a pair of electrodes provided on both surfaces of the piezoelectric vibration element 3 and the pair of leads 5 are connected. The solder plating layer 2 is formed on the outer peripheral surface of the base 4. The cap 1 is made of nickel silver as a Cu, Ni alloy, for example, and the solder plating layer 2 is formed on the inner and outer surfaces of the cap 1 as shown in FIG. As shown in FIG. 3C, the base 4 and the cap 1 are hermetically sealed via the solder plating layer 2. Generally, Sn is used as a component of the solder plating layer 2.
The ratio of Pb to Pb is 9: 1.

However, when attaching piezoelectric vibrators and other elements to a printed circuit board and connecting them by soldering, a reflow furnace has recently been used instead of the conventional flow method in which molten solder is sprayed onto the back side of the board for soldering. There is an increasing number of reflow methods in which solder is melted and connected by passing through the inside, but when soldering the piezoelectric vibrator with the piezoelectric vibrating element housed in such an airtight retainer on the board together with the solder, When the piezoelectric vibrator passes through the reflow furnace together with the substrate, the melting start temperature (solidus temperature) of the solder plating layer in the airtight retainer is around 180 ° C., while in FIG. In order to show the relationship between the heating time and the temperature in the reflow furnace, generally, the heating of the substrate and the piezoelectric vibrators and other elements and parts mounted on the substrate is performed once at a temperature of about 150 ° C. Warming held to after total ivy soaking, the temperature is raised heated to a temperature for soldering. The heating temperature for soldering in the reflow furnace is 200 to 260 ° C, often 215 to 260 ° C, depending on the temperature restrictions of the element to be soldered and the type and composition of the solder used for that purpose.
The temperature is set to any temperature between ℃ and heated. Therefore, when solder is applied to the substrate after passing through the reflow furnace, the piezoelectric vibrator is also heated and the solder plating layer formed on the inner peripheral surface of the cap of the airtight retainer melts and scatters, causing piezoelectric vibration. The vibration frequency may change due to attachment to the element, or the airtightness between the base and the cap may not be maintained.

As a countermeasure against this, it was considered to use various materials having high melting points as a plating layer for sealing.

First, when gold was used as the material for the plating layer with a melting point of 1,063 ° C, the melting point of the plating layer was much higher than the temperature of the reflow furnace. Therefore, melting of the plating layer did not occur, and vaporization did not occur. However, it was preferable. Next, an experiment was conducted using lead having a melting point of 327 ° C or a lead alloy having a melting start temperature (solidus temperature) higher than the heating temperature for soldering in the reflow furnace as a plating layer. Even after passing through, the metal layer did not melt and the airtightness between the base and the cap did not deteriorate.

D. Problems to be solved by the invention However, the use of gold as the plating layer is not suitable for mass production because gold is expensive, and when lead or lead alloy is used, the temperature is 200 to 260 ° C.
In the reflow furnace, lead or lead alloy vapor is generated, and adheres to the surface of the piezoelectric vibrating element to change the vibration frequency.

It is possible to use silver having a melting point of 961 ° C. for the plating layer, but since silver is rather hard, there is instability in obtaining airtightness, and its suitability for production and reliability is not sufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a press-fit type airtight retainer for a piezoelectric vibrator, which eliminates such a drawback of passing through a reflow furnace to make a solder connection to a substrate.

E. Means for Solving the Problems The structure of the present invention for achieving such an object is to mount the piezoelectric vibrating element and to attach the piezoelectric vibrating element to the base through which the lead wire connected to the piezoelectric vibrating element is airtightly penetrated. In a press-fitting type airtight retainer of a piezoelectric vibrator configured by press-fitting a cap that holds an oscillating element in an airtight manner, at least the inner surface of the cap and the joint with the base, lead or under one atmosphere Forming a lead-based plating layer made of a lead alloy having a melting start temperature of at least 230 ° C. or higher and at least a temperature at which the press-fit type airtight retainer is heated in soldering, and further forming a lead-based plating layer on at least the surface of the lead-based plating. It is characterized in that a silver plating layer is formed.

F. Action As the plating layer of lead or lead alloy, the melting start temperature is higher than the heating temperature in the reflow furnace from that of lead or the lead alloy whose melting start temperature is 230 ° C or higher depending on the heating set temperature in the reflow furnace. Since the lead alloy having a high temperature is selected to form the plating layer, the airtightness between the base and the cap is maintained as described in the section of the prior art, and it does not melt even in the reflow furnace. However, there is a drawback that lead vapor is generated in the reflow furnace and adheres to the piezoelectric vibrating element.
In the present invention, the surface of the lead or lead alloy plating layer is further formed with a silver plating layer that does not melt or generate vapor even in a reflow furnace, so lead vapor is generated and adheres to the piezoelectric vibrating element. This prevents both the problems of maintaining the airtightness in the airtight retainer and preventing the metal vapor from adhering to the piezoelectric vibrating element.

G. Examples Hereinafter, the present invention will be described in detail based on Examples shown in the drawings.

When a lead-based plating layer made of lead or a lead alloy is formed on the inner surface of the cap, there is a problem in that lead vapor is generated, and therefore the present invention is based on at least the surface of the lead-based plating layer formed on the inner surface of the cap and further a silver plating layer. Is formed thin to prevent the generation of lead vapor.

If a lead-based plating layer is also formed on the surface of the base, a thin silver plating layer should be formed on the surface of the lead-based plating layer other than at least the outer surface of the press-fit type airtight retainer. To prevent lead vapor.

FIG. 1 (a) is an enlarged view of part A of the cap 1 shown in FIG.
As shown in, the melting start temperature (solidus temperature) is at least 230 so as not to melt lead or the reflow furnace only on the inner surface of the cap 1 (at least the joint with the base).
A lead-based plating layer 7 made of a lead alloy having a temperature of not less than 0 ° C. and not less than the heating temperature in the reflow furnace is formed, and a silver plating layer 6 is formed on the surface of the lead-based plating layer 7. The lead-based plating layer 7 has a thickness of about 10 μm for the purpose of making the space between the base and the cap airtight, and the silver plating layer 6 may have a thickness of about 3 μm for the purpose of preventing the generation and scattering of lead vapor.

On the other hand, it is not necessary to make a soft metal plating on the outer peripheral surface of the base to which the cap 1 is joined, and a plating layer having no plating layer or a nickel plating layer having no sealing action may be formed. Alternatively, a lead-based plating layer and a silver plating layer thereon may be formed on the outer peripheral surface of the base, similarly to the inner surface of the cap 1.

The lead-based plating layer and the silver plating layer may be formed on the cap only at least on the joint surface with the base, and may be formed only on the joint surface on the inner peripheral surface of the cap as shown in FIG. 1 (a). , Fig. 1 (b) due to manufacturing and other reasons.
It may be formed on both inner and outer surfaces of the cap 1 as shown in FIG.
The silver plating layer 6 on the outer peripheral surface of the cap in FIG. 1 (b) may be omitted. Alternatively, as shown in FIG. 1 (c), only the silver plating layer 6 may be formed on the outer surface.

Next, the operation of the press-fitting type airtight retainer for such a piezoelectric vibrator will be described.

In the reflow furnace to set the piezoelectric vibrator with the piezoelectric vibrating element airtightly housed in the airtight retainer configured as described above on the board together with the solder, and to solder for connection with the circuit on the board The lead or lead-based plating layer 7 does not melt because the melting start temperature of the lead or lead-based plating layer 7 is at least 230 ° C. or higher and is higher than the temperature in the reflow furnace. The airtightness with the cap is reliably maintained. Further, since the silver plating layer 6 is formed on the surface of the lead or lead-based plating layer 7, the silver plating layer 6 prevents the generation and scattering of lead-based vapor, and the lead-based vapor adheres to the piezoelectric vibrating element. The vibration frequency of the piezoelectric vibrating element does not change due to.

Next, the results of experiments using an airtight retainer configured by changing the components of the lead-based plating layer are shown below.

Piezoelectric vibrator in which a piezoelectric vibrating element is housed in an airtight retainer in which a lead plating layer containing only lead (melting point: 327 ° C) is formed on the inner surface of the cap and a silver plating layer is formed on the surface of the lead plating layer. According to the graph of the heating history in the reflow furnace shown in FIG. 5, a heat history of 230 ° C. and 260 ° C. and a heat history of 300 ° C. exceeding the actual temperature range in the reflow furnace were added. The actual heat history in the reflow furnace is usually only once, but in the experiment, the heat history was repeatedly added 5 times each. As a result, the airtightness was completely maintained in all cases, and the vibration frequency was obtained as shown in FIG. 3 (a) with the heat history of 300 ° C. added. In the figure, the horizontal axis represents the number of times the heat history is given, and the vertical axis represents the frequency fluctuation of the piezoelectric vibrating element. Recognize. The same applies to those with heat history of 230 ℃ and 260 ℃.
The fluctuation of the vibration frequency was not observed until the third time, and the fluctuation amount after the third time was even smaller than when the thermal history of 300 ° C was added.

Next, about 12% by weight of tin (Sn) is added to lead, and the melting start temperature (solidus temperature) is 250 at 1 atm (101,325 Pa).
A piezoelectric vibrator having a piezoelectric vibrating element housed in an airtight retainer in which a lead-based plating layer of an alloy having a temperature of ℃ is formed on the inner surface of the cap and a silver plating layer is formed on the surface of the lead-based plating layer.
When a heat history at 230 ° C. was repeatedly applied 5 times according to the graph shown in FIG. 5, no abnormalities occurred with the same result as above.

Finally, a lead-based plating layer of an alloy made by adding about 14% by weight of tin (Sn) to lead and having a melting start temperature (solidus temperature) of 230 ° C under one atmospheric pressure (0.101 megapascals) is formed. A thermal history of 200 ° C was applied to a piezoelectric vibrator containing a piezoelectric vibrating element in an airtight cage that was formed on the inner surface of the cap and had a silver plated layer formed on the surface of the lead-based plated layer according to the graph shown in Fig. 5. When added repeatedly 5 times, no abnormalities occurred with the same result as above.

A piezoelectric vibrator with a piezoelectric vibrating element housed in an airtight retainer with only a plating layer made of lead or a lead alloy shown in the section of the prior art formed inside the cap, and repeatedly repeated 5 times at various temperatures of 200 to 260 ° C. However, since the lead-based vapor is generated and adheres to the surface of the piezoelectric vibrating element, the vibration frequency of the piezoelectric vibrating element is
As shown in the representative example in FIG.

Thus, by forming the lead-based plating layer and the silver-plated layer on the bonding surface of the base at least in the cap, it is not always necessary to form the lead-based plating layer and the silver-plated layer on the outer peripheral surface of the base. The airtightness of the airtight retainer can be maintained and the vapor can be prevented from scattering. On the contrary, if the lead-based plating layer and the silver-based plating layer are formed only on the outer peripheral surface of the base and the lead-based plating layer and the silver-based plating layer are not formed on the inner surface of the cap, stable airtightness can be obtained by press fitting. Is difficult.

As a component of the lead alloy forming the plated layer, an alloy of lead and antimony (Sb) or the like may be used in addition to the above-described alloy of lead and tin.

H. Effects of the Invention As described above, according to the present invention, at least the inner surface of the cap in the airtight retainer for forming the piezoelectric vibrator by hermetically housing the piezoelectric vibrating element, the joint with the base. Lead or a lead alloy whose melting start temperature (solidus temperature) under one atmosphere (0.101 megapascal) is at least 230 ° C or higher and which is higher than the temperature at which the press-fit type airtight retainer is heated during soldering. Since a lead-based plating layer is formed, and a silver plating layer is further formed on the surface of at least the lead-based plating layer, even if the piezoelectric vibrator mounted on the substrate passes through the reflow furnace for soldering, The metal vapor is not generated and adheres to the piezoelectric vibrating element to change the vibration frequency, or the airtightness between the base and the cap is not deteriorated.

[Brief description of drawings]

1 and 2 relate to an embodiment of an airtight retainer for a piezoelectric vibrator according to the present invention. FIGS. 1 (a) to 1 (c) are enlarged views of a portion A of FIG. 2, respectively, and FIG. 2 is a cap. 4 is a cross-sectional view of FIG. 3, FIG. 3 is a graph showing the relationship between the number of times heat history is given to the airtight retainer and frequency fluctuation, and FIG. Is a block diagram before the cap is covered, No. 4
Figure (b) is a block diagram after the cap is covered, and Figure 4 (c).
Is an enlarged view of part B in FIG. 4 (b), and FIG. 5 is a graph showing the relationship between heating time and temperature in the reflow furnace. 1 ... Cap, 3 ... Piezoelectric vibration element, 4 ... Base, 5 ... Lead wire, 6 ... Silver plating, 7 ... Lead-based plating.

Claims (1)

[Claims] 1. A base on which a piezoelectric vibrating element is attached and a lead wire connected to the piezoelectric vibrating element is hermetically penetrated,
In a press-fit type airtight retainer for a piezoelectric vibrator, which is configured by press-fitting a cap for hermetically retaining the piezoelectric vibrating element, at least the inner surface of the cap and the joint portion with the base have lead or a pressure of 1 atm. Forming a lead-based plating layer made of a lead alloy having a melting start temperature under at least 230 ° C. or higher and at least a temperature at which the press-fitting type airtight retainer is heated in soldering, and at least the press-fitting type airtight retainer A press-fit type airtight retainer for a piezoelectric vibrator, wherein a silver plating layer is further formed on the surface of the lead-based plating layer other than the portion on the outer surface side.