JPH04190995A - Autogeneous soldering material and electronic circuit board - Google Patents

Abstract

PURPOSE:To minimize thermal effect on a board and an electronic part and to simplify a soldering process by mixing a component causing exothermic reaction with soldering material. CONSTITUTION:Components of chemicals, etc., mixed in soldering material such as soldering paste, etc., cause exothermic reaction in accordance with external stimulation(light, gas, heating below the melting point of solder, etc.). The solder is heated and melted by the heat emitted in that case to perform solder joining. In this way, it becomes possible to minimize thermal effect on the heard 5 and the electronic part 1 and to join places which can not be heated by laser beam 7, etc., because they are shaded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a self-melting solder material mainly consisting of a solder paste used to connect electrodes when mounting electronic components on a board, an electronic circuit board, and Relating to a solder joining method.

[Conventional technology]

A conventional example is JP-A-59-85394. This document discloses a technique in which a substance that is hardened by heating or ultraviolet irradiation is added to cream solder to prevent chip components from falling off. In the conventional method, solder paste was supplied to a board, electronic components were placed on it, and the electronic components were mounted by heating the board by applying heat directly from the outside, such as by heating the entire board or by heating a portion of the board.

Further, as shown in the above-mentioned prior art, there are examples of mixing chemicals into solder paste and curing it to press electronic components, but reflowing uses a method of applying heat from the outside.

[Problem to be solved by the invention]

These methods of applying heat from the outside include a total heating method and a partial heating method. In general heating methods such as infrared heating, the entire board and electronic components must be heated at a temperature that is a certain margin above the melting point of the solder. There was a problem with damaging weak electronic components.

In addition, partial heating methods such as laser heating only heat the solder parts, so there is little thermal effect on the board and electronic components, but there is a drawback that shadowed parts such as the bottom of the electronic components cannot be connected.

The purpose of the present invention is to heat and melt solder without applying heat from the outside, to minimize the thermal influence on boards and electronic components, and to reduce the size of soldering equipment and to The object of the present invention is to provide a solder material that can simplify the process, an electronic circuit board using the same, and a solder bonding method.

[Means to solve the problem]

In order to achieve the above object, the present invention is a self-fusing solder material characterized in that it contains a component that causes an exothermic reaction. Further, the present invention is a self-soluble solder material characterized in that it contains a component that causes an exothermic reaction when stimulated from the outside. Further, the present invention is a self-soluble solder material characterized by containing a component that causes an exothermic reaction when irradiated with light such as sunlight or solar radiation. Also,
The present invention is a self-soluble solder material characterized by containing a component that causes an exothermic reaction upon contact with a gas such as air or oxygen gas. Further, the present invention is a self-fusing solder material characterized by containing a component that is activated and causes an exothermic reaction when heated to a temperature below the melting point of the solder alloy.

Further, the present invention is a self-soluble solder material characterized by containing a mixture of components whose exothermic reaction gradually progresses over time.

Further, the present invention is a self-soluble solder material characterized in that a component that is encapsulated in microcapsules and causes an exothermic reaction when the microcapsules are ruptured is mixed while being encapsulated in the microcapsules. Here, it is preferable that components that cause an exothermic reaction when they come into contact with each other are encapsulated. Further, the present invention is a self-fusing solder material characterized by a mixture of a plurality of types of components having different heat generation characteristics.

The present invention also provides an electronic circuit board comprising a substrate, a heat dissipation member provided on one surface of the substrate, and an electronic component soldered to the other surface of the substrate, in which the solder is An electronic circuit board characterized in that it is formed of any self-fusing solder material. Here, the allowable temperature limit of the board is preferably lower than the melting point of the solder.

Further, the present invention is characterized in that the solder material is mixed with a component that causes an exothermic reaction when stimulated from the outside at a temperature below the melting point of the solder alloy used, and the solder material is melted by the exothermic reaction to perform soldering. This is a soldering method. Here, it is preferable that a plurality of types of solder alloys with different melting points are used, and each solder alloy is mixed with a different component that causes an exothermic reaction at a different temperature.

In addition, the present invention provides a method of supplying a solder material containing microcapsules containing individually encapsulated components that cause an exothermic reaction when they come into contact with each other at a temperature below the melting point of the solder alloy used, and then applying pressure to the substrate. By adding , the microcapsules are destroyed and an exothermic reaction is caused.
This is a solder joining method characterized by melting a solder material and performing solder joining.

In addition, the present invention provides a method of supplying a solder material containing a mixture of multiple types of components with different heat generation characteristics to a substrate, and then causing each component to undergo an exothermic reaction in a stepwise manner to melt the solder material and perform solder bonding. This is a soldering method characterized by:

Furthermore, the present invention includes mixing a plurality of chemicals that generate heat when they come into contact with the solder material on the board side and the electronic component side separately,
This is a soldering method characterized by causing an exothermic reaction by bringing the two into contact, and melting the solder by the reaction heat to perform solder joining.

[Effect]

Components such as chemicals mixed into solder materials such as solder paste cause an exothermic reaction due to external stimulation (light, gas, heating below the melting point of the solder, etc.) or the passage of time.

The heat released at this time heats and melts the solder, making solder joints.

This minimizes the thermal influence on the board and electronic components, and also enables connections in areas that are shaded and cannot be heated with lasers or the like.

According to the method of the present invention, it is possible to solder a printed circuit board with low heat resistance, such as a paper phenol board, without causing large thermal distortion.

Furthermore, if used when repairing some parts on a printed circuit board, parts can be replaced without affecting contact with other parts.

〔Example〕

A first embodiment of the present invention will be described below. In the present invention, a chemical is mixed with a solder material such as a solder paste, and the reaction heat of the chemical heats the solder to perform a connection.

Chemicals that can be used for such purposes must meet the following conditions:

1) Generate enough reaction heat to melt the solder.

2) It should not react with substances constituting solder such as Pb, Sn, and Bi, and with flux.

3) After the reaction, reaction products vaporize and are discharged to the outside of the solder together with the flux.

4) Be solid or liquid at around room temperature.

5) It must have the property that a reaction is induced by light such as ultraviolet rays, oxygen gas, or heat below the melting point of the solder.

An example of a chemical that meets these conditions is benzoyl peroxide (hereinafter referred to as BPO).

BPO is a peroxide and is stable at room temperature, but 1
When heated to around 00°C, a violent decomposition reaction occurs and heat is released. This is made into particles of the same size as the solder particles and mixed into the solder paste. This makes it possible to supply solder paste without significantly changing its supplyability.

Note that since BPO is difficult to dissolve in organic solvents such as alcohol contained in the solder paste, there is little change in quality even if some time passes.

Any solder alloy can be used as long as it has a melting point of 100'C or higher. Here, the use of Pb-8n eutectic solder (6/4 solder, melting point 180° C.), which is generally widely used, will be considered. The use of lower melting point solder alloys and high melting point joining materials (such as silver solder) can also be used by varying the type and amount of chemicals.

This self-melting solder paste is supplied to the bonding pads on the substrate, and after electronic components are mounted, it is heated to about 100°C. As a result, the decomposition reaction of BPO progresses, and the solder is further heated by the heat of the reaction. The reaction peaks when the temperature of the solder exceeds the melting point, and after that the temperature begins to drop.
Adjust the amount. Thereafter, the temperature decreases to below the melting point of the solder, and the bonding is completed.

CO2 and benzene groups are produced as reaction products, but these do not affect the properties of the solder because they are released into the atmosphere or discharged to the outside of the solder together with the flux.

Please note that this BPO may undergo a decomposition reaction due to impact, friction, etc., and even if the temperature does not rise to 100°C, it may decompose if kept at 75°C to 80°C for a long time, so please do not store it. and care must be taken when handling.

Here, an example of how to determine the amount of BPO added to the solder paste will be explained. The specific heat of solder is 0.0
42 cal.g-1.k-'. Also, the ratio of solder to flux in the solder paste is approximately 8:2. Therefore, the amount of heat Q required to heat the solder in 1 g of paste from room temperature (25° C.) to 2'20' C, which is the soldering temperature, is calculated as follows.

Q=0.042xO, 8x (220-25)=6.5
5cai The amount of heat corresponding to this amount of heat can be given by reacting BPO. BPO is combusted by vibration, heating, etc., and the heat of reaction is 180.6 cal/g. Therefore, if 0.04 g of BPO is added to 1 g of solder paste, the amount of heat required to melt the solder can be obtained.

A second embodiment of the present invention will be described below. In the first embodiment, B'P, which reacts with heat below the melting point of the solder, is used as a chemical mixed into the solder paste.
I am using O.

In addition to heat, chemicals that are activated by one or more external stimuli such as light such as ultraviolet rays, or contact with gases such as air, O2, CO2, etc., and cause an exothermic reaction. It is also possible to mix it into solder paste and apply the stimulus to cause a reaction, heat the solder, and bond. Furthermore, irradiation with radio waves, magnetic field lines, X-rays, etc. can also be used as a stimulus to induce a fever reaction.

The heating temperature is adjusted by changing the amount of chemicals mixed. In the case of a chemical whose reaction is terminated by removing a stimulus such as light, gas, or heat, the stimulus can be removed when the appropriate temperature is reached.

Furthermore, by supplying solder pastes mixed with different chemicals onto the same board, it is possible to set a time difference in connection within the board or to join multiple types of solder at the same time.

A third embodiment of the present invention will be described below. By mixing multiple chemicals that cause a slow reaction into the solder paste, after the solder paste is supplied to the board, an exothermic reaction gradually progresses, thereby increasing the temperature of the solder and forming a solder joint. It is possible.

In this method, it is desirable to mix the chemicals immediately before supplying the solder paste to the board to allow time for supply and mounting of the electronic components. However, if there is sufficient time for the reaction, it is also possible to mix the chemicals in the solder paste in advance and supply them to the substrate once the reaction has progressed to a certain extent.

A fourth embodiment of the present invention will be described below. - Multiple types of chemicals that cause exothermic reactions when mixed or brought into contact at the same time are separately put into microcapsules and mixed into solder paste, and the solder paste is supplied onto the board and electronic components are mounted. After that, by applying pressure, vibration, etc. to the solder paste, the microcapsules are destroyed, and the chemicals inside are mixed or brought into contact, causing an exothermic reaction, which heats the solder and performs bonding.

The chemicals to be placed in the microcapsules are one or more of the plurality of chemicals mentioned above, and the remaining chemicals are placed in separate microcapsules and mixed in the solder.

1. A fifth embodiment of the present invention will be described below. - A plurality of chemicals that cause an exothermic reaction when mixed or brought into contact with each other are mixed into separate solder pastes and supplied to the electronic component side and the board side, respectively. Then, when the electronic component is mounted on the board and the solder paste on the electronic component side and the board side come into contact, an exothermic reaction occurs, the solder is heated, and the solder is bonded.

Note that such a reaction can be further stimulated by light, gas, heat, etc. to promote the reaction.

A sixth embodiment of the present invention will be described below. Multiple chemicals that do not interact with each other are mixed into the solder paste. Each of these chemicals has different stimuli that trigger reactions, and by applying these stimuli at different times and allowing different types of reactions to proceed step by step, the temperature gradient during heating can be reduced. to have a change.

For example, a first chemical that generates heat over time and a second chemical that generates heat in response to ultraviolet light are mixed into the solder paste in advance. After this solder paste is supplied to the board and electronic components are placed on it, it is left for a while and heated to a certain temperature by the reaction of the first chemical, thereby performing preheating. Thereafter, ultraviolet rays are irradiated to cause the second chemical to react, heat the solder to its melting point, and melt the solder, thereby performing solder bonding.

Preheating in this manner makes it easier to activate the flux and improves the reliability of the connection.

A seventh embodiment of the present invention will be described below. Consider the case where electronic components are mounted on a board with a low heat resistance temperature, such as a paper phenol board, using a chip on board (C0B) method using solder whose melting point is higher than the heat resistance temperature of the board.

FIG. 1 shows a vertical cross-sectional view of an electronic component mounting portion of a substrate, such as a semiconductor device, for example. In this case, if the entire substrate heating method is used, the entire substrate 5 will be exposed to a temperature higher than the melting point of the solder, so there is a risk that the substrate 5 will be damaged. Furthermore, it becomes difficult to achieve dimensional accuracy.

Furthermore, if the connection is made using a partial heating method such as laser heating, the laser 7 can somehow be applied to the solder bump 3 on the outermost periphery, as shown in FIG.
The laser 7 cannot reach the solder bumps 3a directly below the electronic component 1, such as a semiconductor chip, and the connection cannot be made. Therefore, the self-melting solder paste of the present invention is used for solder connections in such places. In the figure, 2 and 4 indicate connection pads.

In this case, it is not possible to use a solder paste mixed with a chemical that accelerates the reaction when irradiated with light, so a solder paste mixed with a chemical that reacts with gas or heat, or a chemical that generates heat over time, is used. Heat is obtained by reacting the chemicals and heats the solder.
Make solder connections. Note that when using a chemical that reacts with heat, it is necessary to use a chemical whose reaction initiation temperature is lower than the heat-resistant temperature of the substrate.

Furthermore, the back side 1 of the connection part of the board 5. : If the heat dissipation plate 6 is provided, the thermal shape P given to the substrate can be made smaller.

By using this method, it is possible to minimize the thermal effect that sometimes has on the board during soldering, and it is possible to solder to a board with a low heat-resistant temperature as mentioned above, which was previously impossible. COB electronic components using expensive solder
It is now possible to install the vehicle using this method.

Moreover, if the connection method 7.2 is utilized, it can also be used for thermally weak flexible substrates, liquid crystal substrates, etc.

An eighth embodiment of the present invention will be described below. In the examples so far, we have mainly described the method of mixing chemicals that cause an exothermic reaction into the solder paste, but this method can also be applied to cases other than solder paste, that is, granular solder and linear solder. This is possible by using a method such as mixing a chemical into a flux and supplying it without causing an exothermic reaction.

〔Effect of the invention〕

According to the present invention, heat can be applied from the outside to melt the solder, so solder connections can be made with minimal thermal effects on the board and electronic components. ,〕is.

In addition, it is now possible to mount electronic components using solder with a melting point higher than the heat resistant temperature of the board using the PCOB force method, which would otherwise be impossible to use. 9

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the second part of the electronic component holder lj. 1.Electronic components, 2.R child component side connection bat, 3.
・Hanbubi bump, 3a・Outermost bump, 4
・Board side connection pad, 5... Board, 6 Heat sink, 7
1 No-zer.

Claims (16)

[Claims] 1. A self-fusing solder material characterized by a mixture of components that cause an exothermic reaction. 2. A self-soluble solder material that is characterized by a mixture of components that cause an exothermic reaction when stimulated from an external source. 3. A self-soluble solder material characterized by containing a component that causes an exothermic reaction when irradiated with sunlight, solar radiation, etc. 4. A self-soluble solder material characterized by a mixture of components that cause an exothermic reaction upon contact with gases such as air and oxygen gas. 5. A self-fusing solder material characterized by a mixture of components that activate and cause an exothermic reaction when heated to a temperature below the melting point of the solder alloy. 6. A self-soluble solder material characterized by a mixture of components that gradually undergo an exothermic reaction over time. 7. A self-soluble solder material characterized in that a component that is encapsulated in microcapsules and causes an exothermic reaction when the microcapsules are ruptured is mixed while being encapsulated in the microcapsules. 8. The self-fusing solder material according to claim 7, characterized in that components that cause an exothermic reaction when they come into contact with each other are enclosed. 9. A self-fusing solder material characterized by a mixture of multiple types of components with different heat generation characteristics. 10. An electronic circuit board comprising a substrate and an electronic component soldered to one surface of the substrate, characterized in that the solder is formed of the self-melting solder material according to any one of claims 1 to 9. electronic circuit board. 11. 11. The electronic circuit board according to claim 10, wherein the heat resistant temperature of the board is lower than the melting point of the solder. 12. A soldering method characterized in that a solder material containing a component that causes an exothermic reaction in response to an external stimulus is melted by the exothermic reaction at a temperature below the melting point of the solder alloy used, and the solder is joined. 13. 13. The soldering method according to claim 12, wherein a plurality of solder alloys having different melting points are used, and each solder alloy is mixed with a different component that causes an exothermic reaction at a different temperature. 14. After supplying a solder material mixed with microcapsules containing individually encapsulated components that cause an exothermic reaction when they come into contact with each other at a temperature below the melting point of the solder alloy used, the microcapsules are released by applying pressure. A soldering method characterized by breaking the capsule and causing an exothermic reaction to melt the solder material and perform solder joining. 15. A solder joint characterized by supplying a solder material that is a mixture of multiple types of components with different heat generation characteristics to a board, and then causing each component to undergo an exothermic reaction in a stepwise manner to melt the solder material and perform solder bonding. Method. 16. Multiple chemicals that generate heat when they come into contact are mixed separately into the solder material on the board side and electronic component side, and when the two come into contact, an exothermic reaction occurs, and the heat of the reaction melts the solder, creating a solder joint. A soldering method characterized by: