JPH0240425B2 - - Google Patents

Description

Claim 1: A soldering device for fluxless soldering of an assembly containing solder, comprising a container containing a material that can be liquefied at a soldering temperature and an inert material that evaporates at the soldering temperature, and a container that is connected to the container. heating means for heating the liquefiable material to a soldering temperature, the liquefiable material in turn heating the inert material to the soldering temperature and discharging inert vapor into the container; heating means adapted to create an atmosphere; vibration means connected to the container for vibrating the liquefiable material; and fixing the assembly for a sufficient time to melt the solder in the inert vapor atmosphere. and positioning means for positioning the assembly and suspending the assembly on the surface of the liquefiable material, vibrating the assembly and continuously melting the solder contained therein at the same time. A soldering device that achieves fluxless soldering.

2. The soldering apparatus according to claim 1, further comprising a second container arranged at the bottom of the container and adapted to hold the liquefied material, and the vibrating means is connected to the second container. Soldering equipment connected to the container.

3. The soldering apparatus according to claim 2, further comprising means proximate to the top of the container for preventing escape of an inert vapor atmosphere therefrom.

4. In the soldering apparatus according to claim 3, the means for preventing the inert vapor atmosphere from escaping comprises a soldering coil provided within the container adjacent to the top of the container. attaching device.

5. In a fluxless soldering method, the steps include: preparing a container containing a liquefiable material that becomes liquid at the soldering temperature and an inert material that evaporates at the soldering temperature; and heating the liquefiable material to the soldering temperature. the liquefiable material then heating the inert material to the soldering temperature to create an inert vapor atmosphere within the container; and placing an assembly including the solder in the inert vapor atmosphere. floating the assembly on the surface of the liquefied material and exposing a solderable area of the assembly to the inert vapor atmosphere; simultaneously vibrating the liquefiable material while melting the solder in the inert vapor atmosphere to achieve fluxless soldering.

6. In the method described in claim 5,
The above method, wherein the liquefiable material includes solder.

7 In the method described in claim 5,
The above method, wherein the inert material is a large molecular weight halogenated organic material.

8. In a fluxless soldering method for assemblies containing solder, heating the liquefiable material to a soldering temperature;
heating an inert material such that the liquefiable material then becomes a vapor at the soldering temperature to create an inert vapor atmosphere above the liquefiable material; melting the solder by placing it in a steam atmosphere for a sufficient period of time; suspending the assembly on the surface of the liquefied material to expose the surface to be soldered to the inert steam atmosphere; vibrating the liquefiable material and the floating assembly while continuing to melt the solder to achieve fluxless soldering of the assembly.

9. The method of claim 8, wherein the liquefiable material comprises solder.

10. The method of claim 8, wherein the inert material is a high molecular weight halogenated organic material.

BACKGROUND OF THE INVENTION The present invention relates to a soldering apparatus and method whereby solder-containing assemblies are subjected to both steam heat treatment and ultrasonic vibration at the same time to reduce flux (a substance applied to the joint). Soldering without soldering (hereinafter referred to as fluxless soldering) is realized. Such methods and apparatus are particularly useful for assemblies that are susceptible to cleaning operations in preparation for soldering and solder flux application.

A typical printed circuit board has a circuit network formed on one surface and individual components on the opposite surface. The leads on these discrete components are openings through the printed circuit board and extend onto the printed circuit side. Now, the printed circuit board is soldered to complete the circuit network described above. The board is cleaned and fluxed, and the printed circuit side is brought into contact with pure solder. The solder wave ensures a clean surface. The molten solder wets the printed circuit and leads, resulting in a reliable solder joint.
Another way in which such solder wettable surfaces can be achieved is by employing molten ultrasonic solder pots. In this case, ultrasonic energy can move the solder over the wettable surfaces of the printed circuit and leads, thereby removing oxides, fluxes, and impurities, resulting in a reliable soldering operation. realizable. In either case, the flux is necessary to maintain a wettable surface until direct contact with the solder. Such soldering systems are useful for applying solder to connections that are prepared for application of solder from a pot.

Vapor phase soldering refers to a system in which an assembly containing solder is heated in the vapor to a soldering temperature. This steam provides an inert atmosphere and provides heat to bring the assembly up to soldering temperature. Such vapor phase soldering is useful in situations where solder is already present in the assembly and is forced back into the joint by heating. Such soldering is accomplished in a furnace, and the use of an inert gas within the furnace helps achieve a highly reliable solder connection. However, if the surfaces are to be rejoined by solder, it must be cleaned and free of oxide fluxes and impurities, and this must be at soldering temperatures for reliable soldering. It is sometimes required.

Current soldering systems do not permit reliable soldering of assemblies containing devices that are subject to deleterious effects from cleaning and fluxing operations. Such devices include semiconductor chips and thin film circuits. Therefore, there is a need for a soldering apparatus and method that can contact and/or electrically connect components including such semiconductor devices to a substrate.

SUMMARY OF THE INVENTION To better understand the present invention, the soldering apparatus and method of the present invention provides for soldering an assembly having solder between two parts of the assembly at a temperature high enough to melt the solder. This method is characterized in that solder bonding is performed between these two parts by exposing them to an inert gas and at the same time applying vibrations that cause relative movement between these two parts.

Accordingly, it is an object and advantage of the present invention to provide a soldering apparatus and method as follows. That is, in this device, one of the two parts is susceptible to and protected from normal solder joint cleaning and fluxing operations, resulting in highly reliable solder bonding. .

In accordance with another object of the invention, the assembly is heated and vibrated simultaneously by heating the assembly by means of a high temperature inert gas encapsulated in a vessel and a high frequency vibration source. It is an object of the present invention to provide a soldering device and method that can ensure proper solder bonding.

Another object of the present invention is to suspend the assembly to be soldered above the fluid soldering pot by re-inflowing the solder, and to vibrate the fluid solder at a high frequency, thereby applying vibrations to the assembly while An object of the present invention is to provide a soldering apparatus and method characterized by exposure to a high temperature inert gas, the inert gas being sufficiently hot to melt re-entered solder in the assembly.

Other objects and advantages of the invention will become apparent by reference to the following portion of the specification, claims, and accompanying drawings.

[Brief explanation of drawings]

FIG. 1 is a vertical center cross-sectional view of a soldering apparatus according to the invention, with the cover, cooling coil and solder pot depicted in an enlarged side view.

FIG. 2 is a perspective view, partially cut away, of an assembly to be soldered with the apparatus and method of the present invention.

DESCRIPTION The soldering apparatus of the present invention in combination with the soldering method of the present invention is generally designated at 10 in FIG. This device is provided with a base 12, which supports a soldering pot (hereinafter abbreviated as "pot") 14.
This pot 14 contains solder 16,
This is shown in a cutaway view near the edge of the pot. The solder is heated by a heater coil 18 so that the solder 16 becomes a liquid (fluid) state. This coil 18 is installed so as to encompass the pot 14. A heater power supply 20 supplies heater power. A feedback is provided to the heater power supply to control the heater power and maintain the solder 16 at a preselected temperature. An electromechanical transducer 22 is secured to this pot. Power is supplied to the transducer 22 from a power source 24, and high frequency power is applied to the transducer 22 by the power source 24. This frequency is preferably ultrasonic or a frequency close to it. Transducer 2
2 to the solder pot 14, and the power supply 2
4, this transducer 22 supplies high frequency waves such as ultrasonic vibrations to the solder 16.

A support plate 24 is placed on the base 12 and an opening is formed therein. Solder pot 1 is inserted into this opening.
4 is installed. Wall 26 is provided with a vessel wall, to which support plate 24 and solder pot 14 form a bottom. As shown in FIG. 1, the overall structure is generally square or rectangular in the horizontal direction, but circular cylindrical in the vertical axis.
The walls 26 are double-walled with an inner skin 28, an outer skin 30, and thermal insulation 32 therebetween. The vessel 34 thus defined is closed by the cover 36 and the inner space 38 is enclosed. The cover 36 can be moved to access this interior space.

A cooling coil 40 is mounted around the upper inside of this vessel. The coil 40 is provided with a fluid inlet 42 and a fluid outlet 44, which allow a cooling zone to be created in the upper portion of the vessel. By using this cooling coil,
The steam produced in space 38 can be condensed to prevent it from escaping from the top of the vessel when the device is in use. The fluid employed in this cooling coil is related to the evaporation point of the heating fluid employed within the interior space. According to the present example, adequate condensation of this vapor is achieved when room temperature water is utilized as the fluid in the cooling coil together with the evaporative materials described below. The material within interior space 38 is in a vapor state at operating temperatures. This preferred material is
A large molecule halogenated organic material, this material is Nabumoto FC70, available from 3M Company, St. Paul, Minn. This cooling material evaporates at 215°C, is inert with respect to the solder material, and
It is also inert to most assemblies with solderable joints. This fluid has a vaporization point (evaporation point) of 215°C and is a suitable material;
It is compatible with most solders. If multi-step soldering operations are required, there is FC71, also available from 3M, which has a vaporization point of 253°C. Intermediate temperatures can be obtained by mixing these two fluids in appropriate proportions.

In order to better understand the use of the apparatus of the invention, an example of an assembly to be soldered by the apparatus and method of the invention is shown in FIG. The assembly 50 includes a chip 52 on which a plurality of semiconductor electronic devices are mounted. The chip 52 is mounted using epoxy onto a chip carrier 54, which is a ceramic support for supporting the chip. Before the chip 52 is fixed, the chip carrier 54 is silkscreened, etched, or has leads plated thereon. The leads are shown extending around the edges of the chip carrier from a pad on the top of the chip carrier to its bottom corner. At this bottom corner, the leads can be wetted with solder. The pads on the chip are connected to the pads on the chip carrier by lead wires, such as lead wire 60 connected to the pads on lead 58.

Problems arise in supporting, fixing, and connecting these chip carriers to these leads. Assembly 50 is provided with a substrate 62, which is also ceramic. A plurality of leads and pads are silk screened onto the top of this substrate 62. Leads 64, 66 are specifically represented as a plurality of such leads. lead 6
8 and 70 are shown connecting between chip carrier 54 and other chip carriers and/or other discrete devices mounted, screen printed, plated or etched onto substrate 62. The leads on the board are terminated one dimension below the edge of the chip carrier 54. The termination of lead 72 is shown at the edge of the chip carrier shown in phantom. Board 6
The top leads and pads of 2 are silk screened in place or applied by other conventional methods.

In addition to the leads and pads, a plurality of mounting squares are silk screened onto the top surface of substrate 62. The location of these squares is such that they act as contact points and are located on the underside of the chip carrier 54. Two of these contact points are indicated at 74 and 76. These points are spaced apart from the leads mentioned above. These points are used to contact and bond the chip carrier to the top surface of the substrate, creating not only a physical connection of the chip carrier to the substrate, but also a good thermal path between these elements. In FIG. 2, a plurality of small contact points are provided, but a small number of large contact points may be provided if desired.

The method and apparatus of the present invention utilize a chip carrier 5
4 to the substrate 62 is particularly preferred.
Areas on the substrate 62 to be soldered to the chip carrier 54, such as the thermally conductive areas of the leads and/or contact points 74, 76 just below the edges of the chip carrier 54, are provided with a controlled amount of solder. , this solder is allowed to flow and wet these areas before introducing the chip carrier 54. Cooling fluid cooling coil 4
0 to energize the heater coil 80, and inert gas material (inert atomosphere).
matenal) in space 38. Solder tank 1
Heat this inert material by 6. This material is a fluid at room temperature and when heated to vaporize creates vapor in the active interior space of the Bethel at a temperature high enough to melt the solder. Since this vapor is heavier than air, it will remain in this vessel. However, in order to prevent this vapor from disappearing, the upper layer of the vapor is condensed by the cooling coil 40.
This will return by lowering the inner walls of Bethel. Since the power supply 24 is energized,
The solder bath 16 can be vibrated at high frequency.

Once the solder has melted and a suitable temperature has been reached at which melting of the inert gas material occurs at least at the soldering temperature, the assembly 50 of FIG. 2 is delivered. The assembly 50 is provided with a chip carrier 54 located on top of the substrate 62. This assembly 50 cannot be cleaned or fluxed. The reason for this is that the semiconductor chip 52
This is because there exists flux and the flux falls between the chip carrier 54 and the substrate 62. Problems will arise if it cannot be completely removed. Holding the assembly with a clamp, template, or other positioning device, cover 36 is removed and the assembly is slowly lowered into the vessel. The assembly remains in the vapor zone long enough to substantially melt the solder. This assembly 50 is floating on the solder 16 which is subjected to high frequency vibrations. This vibration cleans the surface, and when there is no flux, a solder surface free of impurities is obtained, and these can be reliably joined. This bonding includes fixing the chip carrier 54 to the substrate 62. This is secured by melting solder to the contact points, including contact points 74 and 76. The solder at these contact points contacts the underside surface of the ceramic chip carrier 54, thereby securing the chip carrier in place and creating a heat conduction path from the chip 52 into the substrate 62. . Additionally, each of these leads 56 and 58 contacts leads 64 and 66 to form an electrical connection from a pad on the chip carrier to a pad on the substrate. In this way, all electrical connections from the chip carrier to the substrate are realized by edge solder bonding processes.

It is important to note that the steam in space 33 is an inert gaseous material and provides the basic heat for melting the solder. Heat is supplied to this inert gas material by a solder bath 16. Furthermore, this tank 16 allows the assembly 50
can be suspended and in this case a coupling can be established between the transducer 22 and the assembly 50. Therefore, this tank 16 is not necessarily made of solder, but is a liquid whose operating temperature is 20°C to 40°C above the boiling point of the liquid, and when the liquid boils, it releases heating steam. must be of higher density than assembly 50. This allows the assembly to float above the fluid while retaining heat and inert material while being subjected to mechanical vibrations. The aforementioned vapor zone allows the assembly to be soldered to be preheated, and is heated while the assembly is present in the space in the vessel above the solder layer. The zone is also maintained in an inert atmosphere, which prevents solder debris from forming. Furthermore, because heat is added by this steam, the actual soldering temperature is achieved by condensation of the steam, and the ultrasonic energy is applied to the assembly at the soldering temperature, resulting in no flux. , highly reliable soldering can be achieved. That is, the assembly 50 is heated in an inert vapor atmosphere to a temperature sufficient to melt the solder for a sufficient period of time and then lowered into the top of the vessel.
The assembly 50 is then lowered to float on the surface of the liquefiable material, exposing the surface to be soldered to an inert gas atmosphere. The liquefiable material is vibrated, which in turn vibrates the assembly 50. The solder continues to melt on the assembly 50, thereby achieving fluxless soldering.

Note that the inert gas material here is not limited to the above-mentioned halogenated organic material. This is an example of an inert material. Comparable materials include models P70 and P71 available from 3M. Other materials include Fluorinert FC-70, described in U.S. Pat. No. 4,315,042, and FREON ES, manufactured by E.I.
It is. This is also cited in US Pat. No. 3,866,307. Therefore, the inert gas material is not limited to materials having large halogenated molecules as described above.

Although only the best mode of the invention has been described,
It will be readily apparent to those skilled in the art that other modifications can be devised.