JPH0318041A - Electric junction part - Google Patents

Abstract

PURPOSE:To improve stability of re-reflow by connecting electrodes therebetween with solder containing a plurality of metal particles so that the melting point of the particle is higher than that of the solder and all or part of the material of the particle contain a different material from that of the solder. CONSTITUTION:A substrate 11 is formed of an electrode 1 provided on an insulator 4, an electrode 2 provided on a chip component 3, the component 3 and the insulator 4 together with the electrode 1. A solder 5 for connecting the electrodes 1, 2 and electrically conducting them, metal particles 6 dispersed in the solder 5, and a support 9 for securing the component 3 to the insulator 4 are provided. The melting point of the particles 6 is higher than that of the solder 5, and all or part of the material of the particle 6 contains a different material from that of the solder 5. Thus, a thin mounting state of high reliability for re-reflow can be realized.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electrical connection between an electrode provided on an insulator and a chip component or a pair of chips, and in particular to an electrical connection with excellent productivity and reliability. This is related to the department.

[Conventional technology]

Conventionally, when mounting chip components on a printed circuit board, etc., in order to reduce the mounting thickness, a molded packaged component was embedded in the component insertion hole and the leads of the chip component and the electrodes of the printed circuit board were connected using the solder reflow method. was. This method has the advantage that the mounting thickness of the chip components is partially offset by the printed circuit board, making it thinner than the normal surface mounting method. However, because of the lead, this portion remained as a protrusion, and there was a limit to obtaining a thinner mounted bear.

Therefore, by providing electrodes for external connection on the surface, embedding the paired chip components without leads in the printed circuit board, and keeping the paired chips and the electrodes on the printed circuit board on the same plane, they are connected using the solder flow method. It can be mounted thinly due to its protrusion due to its thickness. However, in this method, there is a gap between the paired chips and the electrodes on the printed circuit board, so if normal eutectic solder paste is used, the gap must be made sufficiently small, and it is expensive to insert the paired chips. Positional accuracy is required, and even if it is connected, it has low reliability when reflowing. Although there is a method of using a conductive adhesive instead of solder, it is generally inferior to solder in terms of contact resistance, reliability, and cost, and its applicability is limited.

[Problem to be solved by the invention]

Conventional paired chip mounting methods require strict control of manufacturing conditions, have poor reliability against reflow, and are limited in the fields of application due to contact resistance, cost, etc.

The purpose of the present invention is to eliminate such conventional drawbacks, eliminate the need for particularly high positional accuracy of paired chips, reduce contact resistance,
The object of the present invention is to provide an electrical joint that has performance equivalent to or higher than that of ordinary solder, is thin, and realizes a highly reliable mounting form for reflow.

Furthermore, if the present invention is applied to a normal surface mounting method, chip standing as shown in Figures 6 and 7 due to variations in solder amount will be reduced, manufacturing conditions will be easier to manage, and reflow of the joint will be reduced. It was discovered that subsequent reliability improvements could be achieved, and the present invention was perfected.

[Means to solve the problem]

The present invention provides an electrical junction in which a plurality of electrodes provided on an insulator and a plurality of electrodes provided on a chip component are independently electrically connected, and a plurality of metal grains are included between the electrodes. The plurality of metal particles are connected by solder, and the melting point of the plurality of metal particles is higher than that of the solder, and all or part of the constituent material of the plurality of metal particles includes a material different from the constituent material of the solder. It is an electrical connection.

The chip components applied to the present invention consist of active elements such as Hall elements, transistors, and ICs, and passive elements such as resistors, capacitors, and inductors. There is a form in which the element is packaged with a molding material or the like and lead wires are provided for external connection. Among these, the present invention is particularly effective in the former pair chip form, in which the electrodes are made of a material with good solderability and are formed flat or curved on the surface of the chip.

The electrode on the other side to which the chip component is connected is formed on a flat surface around the chip component, in a stepped position, or in a position facing the chip component, and is made of resin, ceramic, etc.
It is formed on an insulator that contains chemicals. The connecting solder material contains high melting point metal grains in the solder.

Hereinafter, the present invention will be described in detail with reference to a circular plane.

FIG. 1 is a cross-sectional view showing one embodiment of the electrical connection part of the present invention. In the 11th fi, l is an electrode provided on the insulator 4, 2 is an electrode provided on the chip component 3, 3 is the chip component, and 4 is an insulator, which forms the substrate 11 together with the electrode l. As long as this substrate l1 includes at least one set of insulator 4 and electrode l, other layers may be laminated thereon. Reference numeral 5 indicates a solder that connects the electrodes 1 and 2 to make them electrically conductive, 6 indicates metal particles dispersed within the solder 5, and 9 indicates a support for fixing the chip component 3 to the insulator 4. electrode!
, 2 need to have good wettability with the solder 5. In reality, copper, silver, gold, platinum, lead, tin, iron, nickel, indium, aluminum, and stainless steel can be used by selecting a solder that has good wettability with the electrode. Copper, silver, and gold are preferred, and copper is particularly preferred from the economic point of view. It goes without saying that the electrodes 1 and 2 may be manufactured by any method, and the number of electrodes is not limited to two, but may be three or more. In addition, the arrangement of the electrodes 1 and 2 is not limited to the example shown in FIG. 1, but can also be applied to various forms as shown in FIGS. 2(A) to 2(D), for example. In Figure 2 (D),
2' indicates the third electrode.

The distance between electrode 1 and electrode 2 depends on the shape of the electrode and the amount of solder applied, but the shortest distance between them is
0.05mm or more, even 0.1M or more, especially 0.3
In the case of more than one child, the present invention exhibits its effects significantly.

The dimension of the electrode in the direction perpendicular to the connection direction (defined as electrode width) should be 4 times or less, further 2 times or less, and especially 1 time or less as the shortest V distance between the electrodes increases. The effects of the present invention are significantly exhibited.

The material of the solder 5 may be any material as long as it can form an alloy structure with the electrodes and metal grains, and both eutectic and non-eutectic materials can be used. For example, when the electrodes and metal grains are made of copper, alloys containing tin, particularly Sn--Pb alloys, are preferred because of their high bonding strength. Furthermore, if the electrode is not suitable, a Sn-Pb-Ag alloy can also be used.

Note that the term "solder" as used in the present invention means an alloy containing a metal that can form an alloy structure with electrodes and metal grains.

The metal particles 6 need to have a melting point higher than the phase line temperature of the solder 5, and the temperature is 20°C or higher,
Preferably 35°C or higher, more preferably 5Q'C
That's all. In addition, in order to ensure stability against reflow, it is preferable to set the melting point of the metal grains 6 higher than the reflow temperature, and furthermore, all or part of the constituent material of the metal grains is made of a material other than the constituent material of the solder 5. It can also include things like

Ag+Au, Cu,
Pt, Ni, Fe, Aj! , Cd, Zn, and alloys containing one or more of the above metals. In addition, metal grains, glass grains whose surfaces are covered with metals containing any of the above,
Ceramic grains or resin grains may be used, or metal grains of two or more materials may be used at the same time. Among the above, Ag, Au, Cu, Pt, Ni and Cu-based alloys, Au
g alloy, Ag-based alloy, Ni 75 alloy, and metal grains whose surfaces are covered with the above-mentioned metals are preferable, and furthermore, Au. Ag
．． Copper grains made of Ni alone or whose surfaces are covered with any metal or alloy of Au, Ag+Ni, and Sn are preferred.

The particle size of the metal particles is approximately 1 to 150 μm, preferably 1 to 75 μm, and more preferably 1 to 50 μm, considering bonding reliability and processability.

Regarding the shape, an amorphous shape is preferable to a spherical shape because it allows a larger interface area with the solder and is therefore preferable in terms of reliability.

Regarding the amount of metal particles, if the amount of metal particles is too large, the solder cannot fill between the metal particles, resulting in an increase in connection resistance and a decrease in reliability.If the amount is too small, the yield of the connection will be poor, and the parts connected by the present invention may not be solder reflow solder. When the solder is connected to another board or the like by the method, the solder may be remelted due to the reflow heat, and the connection may be disconnected. Specifically, in terms of volume ratio, the value of metal grains/(metal grains + solder) is 0.5 Vol% or more67
%Voffi% or less, preferably 2 Vol% or more and 50 Vol% or less, particularly preferably 5 Vol% or more and 20 Vol% or less.

With the above amount of metal particles, even if the solder at the connection part is remelted, the metal particles dispersed therein will suppress fluidity, so the connection will not break.

A method for obtaining the electrical connections shown in FIG. 1 and FIG. 2 will be explained with reference to FIGS. 3(A), (B) and (C).

Step (1): As shown in FIG. 3(A), a solder paste containing a mixture of solder grains 5A, metal grains 6 and flux 7 is applied onto electrodes 1 and 2 by screen printing or other methods. Adhere to, that is, adhere or apply in a straddling manner.

Step (2): After preheating at a temperature below the phase line of the solder grains 5A, the solder paste is reflowed at a temperature above the in-phase line of the solder grains 5A and below the melting point of the metal grains 6, and then cooled and solidified. . Through this process, the solder grains 5A melt and coalesce, and the unmelted metal grains 6 are dispersed, and a residue generated from the flux in the solder paste remains on the surface of the joint. The reflowed solder is cooled and solidified to form an electrode as shown in Figure 3(B).
The solder 5, metal grains 6, and flux residue 8 provide electrical continuity between and 2.

Step (3): Thereafter, the flux residue shown in No. 31m (B) is removed to obtain an electrical joint as shown in FIG. 3(C).

Although the manufacturing process is simple, the electrical joints obtained in this way do not cause conduction defects due to the height of the swelling caused by the gas generated during reflow or the surface tension of the solder itself. , it is possible to reliably electrically connect the electrodes and establish electrical continuity between the two electrodes.

Furthermore, the bonding strength between the electrode and the solder is high, and the specific resistance of the bonded portion can be significantly lowered. Furthermore, the reliability with respect to reflow is higher than that of the conventional one.

In addition, conduction due to solder bridges occurs when the solder, which is at least partially melted, coalesces with the remaining metal grains during a certain period at the beginning of the reflow process. Once a solder bridge occurs, the solder bridge will be maintained even if the solder is completely molten or subsequently cooled and solidified. In other words, although there are restrictions depending on the dimensions and positional relationship of the electrodes, basically, as long as the above-mentioned solder flow temperature conditions are satisfied, the temperature between the solidus line of the solder grains used and the melting point of the metal grains and above the melting point of the metal grains is basically the same. It can be reflowed at any temperature. The particle size of the solder particles 5A is preferably 15 μm or less, more preferably 7.5 μm or less, considering the printing and coating properties of the solder paste. Furthermore, in order to avoid viscosity deviation, it is preferable to use particles with a uniform particle size.

As the flux 7, resin-based flux, particularly activated resin blacks, is preferable. The main component is a rosin-based natural resin or a modified resin thereof, to which an activator, an organic solvent, a viscosity modifier, and other additives are added. In general, modified resins include polymerized rosin and phenolic resin-modified rosin, activators include inorganic and organic fluxes, especially amine hydrochloride and organic acid-based fluxes, and organic solvents include carbitol-based and ether-based fluxes. things are used. Note that an inorganic flux may be used depending on the type of metal particles.

The amount of flux required is sufficient to cause integration between reflowed solder grains and between solder grains and metal grains, but for example, if the metal grains are copper, the flux should be 5% by weight or more of the solder grains. , preferably 7% by weight or more, more preferably 10ml% or more. Incidentally, as the proportion of metal particles increases, the amount of flux needs to be increased within a range that does not deteriorate printing and coating properties.

The solder paste composed of the solder particles 5A, metal particles 6, and flux 7 described above is attached or applied to the electrode portion by a screen printing method or a method using a dispenser. As shown in FIG. 3(A), the adhesion or coating must be carried out so as to cover all of the electrodes 1 and 2 to be connected. Preheating is used to alleviate the thermal stress on the substrate due to the rapid temperature rise during reflow, and at the same time has the effect of completely dissipating the volatile components in Franks and suppressing the generation of gas during reflow. It is preferable to do this. Preheating conditions vary depending on the material and structure of the board, but
The temperature is lower than the melting point of the solder, preferably 20°C to 60°C lower than the melting point of the solder. For example, in the case of solder with a composition of Sn:Pb=63:37 (common solder), the temperature is 120'C to 160C.
It is preferable to preheat at 'C. If it is too high, the flux will harden and the solder adhesion will deteriorate, and if it is too low, the volatile components of the flux will not be sufficiently dissipated, causing gas retention and causing solder non-wetting. The heating time also varies depending on the heat capacity of the board, the amount of solder paste, the amount and type of flux, the heating method, etc., but preheating should be performed for about 1 to 3 minutes after the surface and inside of the board reach the specified temperature. is preferred.

From the viewpoint of bonding strength, the flow temperature is set to be at least 5°C higher than the melting point of the solder. Furthermore, it is preferable to set the temperature to a temperature higher than 2°C. The upper limit temperature is determined by the heat resistance of the substrate, but care must be taken because if it is too high, the flux will carbonize and lose its activation effect. The time setting is the same as in the case of preheating, but a few seconds or more is sufficient.

Heating methods include hot air heating, infrared heating, pepper phase soldering, laser heating, hot plate, resistance heating, and soldering iron heating, but in order to obtain higher continuity reproducibility, it is necessary to melt the solder. The rate of temperature increase from the start of reflow to the peak temperature of reflow is preferably slow, and hot air heating or infrared heating is particularly preferable.

After reflow, flux residue 8 is left on the surfaces of the solder 5, chip component 3, and insulator 4, as shown in FIG. 3(B), but to remove it, cleaning is necessary. I do. Shower cleaning, ultrasonic cleaning, steam cleaning, etc. may be performed using a chlorofluorocarbon solvent such as trichlorotrifluoroethane or a chlorine solvent such as 1-1-1 trichloroethane as a cleaning agent.

〔Example〕

Next, the present invention will be explained in detail with reference to examples, but the present invention is not limited only to these examples. Example 1 By a known method, a chip component 3 was embedded in a substrate 11 as shown in FIGS. 1 and 4, and an electrode 1 and an electrode 2 of the chip component were formed on the same plane ( Dimensions are 0.3mm x 0.3mm x 0.03I each
IIIlt, 0.2mmX0.2mmX0.03mmt
). Two values of l were prepared: 250 μm and 800 μm.

Next, by screen printing using a metal mask, a solder paste having the following composition was applied onto the two electrodes and 2 so as to straddle these electrodes.

Solder grain material of solder paste Sn/Pb/Ag= 62/36/2
Solder particle size Max. 40 μm Solder particle shape Irregular metal particle material Silver metal particle size Max. 40 am Metal particle shape Irregular flux Weakly activated flux Mixing ratio (volume ratio) (Solder particles): (Metal particles): (Flux) = 90 :
10: 105 Thereafter, after preheating in a hot air oven at 120"C for 10 minutes, reflowing in a hot air oven at 215°C for 3 minutes, and then ultrasonically cleaning with 1-1-1} dichloroethane to clean the surface. The Franks residue was removed to produce an electrical joint as shown in FIG. 3(C).

The resulting joints were reflowed with almost 100% yield in the 3rd lm (C) for both electrode configurations.
As shown in Figure 2, the solder was bridged across two electrodes, and the bonding strength was no inferior to that of normal solder. Further, when reflowing was performed under the conditions of 230″C x 30 seconds, no breakage of the connection portion was observed.

Example 2 By a known method, a chip component 3 was placed on a substrate 11 as shown in FIG. 5, and a step of 150 μm was provided between the electrode 1 and the electrode 2 of the chip component. The dimensions of electrodes 1 and 2 were the same as in Example 1.

Next, the solder paste used in Example 1 was applied so as to span over the two electrodes 1 and 2. After that, 12
After preheating in a hot air oven at 0°C for 10 minutes,
It was reflowed in a hot air oven at 15°C for 3 minutes, and then ultrasonically cleaned with 1-1-1}lichloroethane to remove Franks residue on the surface to obtain an electrical joint as shown in No. 21m(A). .

The resulting joint is almost 100% reflowed solder.
As shown in FIG. 2(A), the solder was bridged across the two electrodes with a yield of 100%, and the bonding strength was no inferior to that of ordinary solder. In addition, 230″CX30sec
When reflowed under these conditions, no breakage of the connection was observed.

Comparative Example 1 Sn/
An electrical joint was obtained in exactly the same manner as in Examples I and 2, except that a solder paste of Pb=63/37 alloy (manufactured by Senju Metal Industry ■, trade name: SPT-55-63) was used. The number of the resulting joints that were bridged so as to span two electrodes was less than 5% in the form of FIG. 4, and 0% in the form of FIG. 5.

Example 3 Four electrodes (0.2 mm x 0.2 mm x 0.03
+um t) of the paste used in Example 1 was applied. The amount of coating was set at one point of the four electrodes to be half the amount of the other three points having the same amount of coating. Thereafter, chip components having electrodes similar in size and position to those on the substrate were set 7 so that the electrodes faced each other.

After that, it was preheated in a hot air oven at 120"C for 10 minutes, then reflowed in a hot air oven at 215°C for 3 minutes, and then ultrasonically cleaned with 14-1} dichloroethane to remove the flux residue on the surface. Figure 2 (
An electrical connection as shown in C) was obtained. The resulting joint is shown in Figure 2 (C) with almost 100% yield of reflowed solder.
As shown in the figure, the solder was bridged across two electrodes, and there was no disconnection due to standing chips, and the bonding strength was comparable to that of regular solder.

Furthermore, when reflowing was performed at 230°C for 30 seconds, no breakage of the connection was observed. Comparative Example 2 Sn/Pb was used instead of solder paste ■ in Example 3.
= 63/37 alloy solder paste (Senju Metal Industry ■
An electrical joint was formed in exactly the same manner as in Example 3, except for using SPT-55-63 (trade name: SPT-55-63, manufactured by Mikko Industries, Ltd.).

In the resulting joint, as shown in FIG. 6, the chip component 3 stood up when the amount of supplied solder was smaller, and it was impossible to bridge the electrodes 1 and 2.

Example 4 Electrical joints were formed in the same manner as in Examples 1 to 3, except that solder pastes 1 to 3 shown in Table 1 below were used. Note that the particle size and shape of the solder grains and metal grains of each paste, and the material of the flux were the same as those of the solder paste.

In all electrical joints, the reflowed solder was bridged across the two electrodes with a yield of almost 100%, and the joint strength was no inferior to that of ordinary solder. Furthermore, after reflowing at 230"CX for 30 seconds, no disconnection occurred at the connection, and the reliability thereafter was also good.

Table 1 [Effects of the Invention] According to the present invention, the gap between the electrode on the chip component and the electrode on the substrate can be made wider than when using a conventional eutectic solder paste, so the positioning of the chip component is easier. Enables high-density packaging without requiring high precision. Furthermore, the contact resistance and reliability of the joint are no different from conventional ones, and the stability against reflow is much improved compared to conventional ones. In addition, if the present invention is applied to a normal surface mounting method, chip standing due to variations in the amount of solder paste applied will be drastically reduced, and as shown in Fig. 2 (A), which was impossible to achieve with conventional solder.
form is also possible.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the electrical joint of the present invention, FIGS. 2(A) to (D) are cross-sectional views showing various embodiments of the electrical joint of the present invention, and FIG. (8) to (C) are cross-sectional views illustrating one embodiment of the manufacturing process of the electrical joint of the present invention, 4th and 5th are perspective views illustrating electrodes in the embodiments of the present invention, and 6th and 7th The figure is a cross-sectional circle showing an example of an electrical joint obtained using a conventional solder paste.

Claims (2)

[Claims] 1. In an electrical joint where a plurality of electrodes provided on an insulator and a plurality of electrodes provided on a chip component are independently electrically connected, the electrodes are connected by solder containing a plurality of metal grains. , and the plurality of metal particles have a higher melting point than the solder, and all or part of the constituent material of the plurality of metal particles includes a material different from the constituent material of the solder. 2. The solder is an alloy containing tin, and the plurality of metal particles are Au, Ag, and Ni alone, or Au, Ag, and Ni.
, Su. , or Su.