JP3864172B2 - Soldering composition - Google Patents

Description

The present invention relates to a soldering composition, and more specifically, a lead-free soldering composition, which is alloyed during reflow soldering to form an alloy with an increased solidus temperature , resulting in The present invention relates to a soldering composition that enables soldering under substantially the same temperature condition when further soldering is performed on a soldered substrate or the like.

  For example, in the production of various electronic circuit devices such as electronic circuit modules, a double-sided mounting type electronic component mounting board is used, and electronic components are mounted on one side of the electronic component mounting board via high-temperature solder, After passing through the furnace and soldering, an electronic component is mounted on the other surface via solder, and then again through the furnace and soldering. Therefore, when an electronic component is soldered to the other surface side of the electronic component mounting board, it is necessary to use a low-temperature solder having a melting point lower than that of the high-temperature solder used on the one surface side. As described above, two kinds of solders having different melting points are generally prepared by adjusting the lead content of the lead-containing solder.

  However, in recent years, from the standpoint of global environmental protection, solder containing no lead (lead-free solder) has been demanded, and lead-free solder has been actively developed. However, a high-melting-point solder that is a lead-free solder and comparable to conventional high-temperature solder containing lead has not been put into practical use at present. The melting point of lead-free solder currently in practical use is about 250 ° C. (246 ° C. for Sn-10Sb) even if it is high.

  For this reason, for example, after soldering an electronic component on one surface of a double-sided mounting type electronic component mounting board using lead-free high-temperature solder, the reflow soldering is performed on the opposite surface at a temperature in the range of 230 to 260 ° C. When the ring is carried out, problems such as the electronic component soldered using the lead-free high-temperature solder floating or dropping from the electronic component mounting substrate occur.

The present invention is a lead-free soldering composition, which is alloyed during reflow soldering to form an alloy with an increased solidus temperature. It is an object of the present invention to provide a soldering composition that can be soldered under substantially the same temperature conditions when it is carried out.

  As a result of intensive studies to solve the above problems, the present inventors, as a soldering composition, consisted of a metal component that melts at a reflow soldering temperature and a metal component that does not melt at the reflow soldering temperature. It was found that the above-mentioned object was achieved by using a metal composition to be converted, and the present invention was completed.

That is, the soldering composition of the present invention do not contain lead, consists of a first metal component and second metal component, the first metal component is a powder of Sn-3.5Ag alloy, the second metal component Is a powder of Ag , and the relative amount of the first metal component and the second metal component is Sn15-24.n by the second metal component being diffused and alloyed in the molten first metal component during reflow soldering . It is a relative amount capable of forming a Sn-Ag alloy composed of 5% by mass and 75.5-85% by mass of Ag .

The soldering composition of the present invention is a lead-free soldering composition. By using the soldering composition of the present invention, an alloy having an increased solidus temperature is formed by alloying during reflow soldering. As a result, when further soldering is performed on a soldered substrate or the like, soldering can be performed under substantially the same temperature condition.

  Conventional high-temperature solder has a melting point of about 280 to 295 ° C., and when soldering using such solder, the reflow temperature has to be set to about 320 to 350 ° C. or more. However, in such a temperature range, thermal stress is applied to the electronic components to be soldered, causing a serious decrease in the reliability of the electronic components. Since it is not possible to use an incompatible paper phenolic resin substrate or the like, it is necessary to use a metal substrate or the like. Therefore, it is desired that thermal stress is reduced and that an ordinary resin substrate can be used, and a high-temperature solder that can be mounted at about 260 to 320 ° C. is desired.

  Assuming that the reflow soldering operation is performed at 260 to 320 ° C., when the melting point is lower than 183 ° C., the wettability contact angle becomes smaller than 50 ° in the molten state during reflow soldering, and short circuit failure If the melting point is higher than 260 ° C, the wettability contact angle becomes larger than 130 ° in the molten state during reflow soldering, and the fixing strength between the component to be soldered and the substrate is low. This is not preferable. Therefore, in this invention, Sn-3.5Ag whose melting | fusing point is 221 degreeC is used as a 1st metal component.

  In the present invention, Ag that is a metal component having a melting point of 400 ° C. or higher that does not melt during the reflow soldering operation is used as the second metal component.

The relative amount of the first metal component and the second metal component is such that the second metal component diffuses into the molten first metal component during reflow soldering and is alloyed to form Sn15 to 24.5% by mass and Ag75.5. Ru relative amounts der capable of forming a Sn-Ag alloy consisting of 85 wt%. In the present invention, the “molten state” includes not only a completely liquid phase but also a state in which a solid phase remains partially.

  The soldering composition of the present invention preferably exhibits a wettability contact angle in the range of 50 ° to 130 ° in the molten state during reflow soldering, and 70 ° in the molten state during reflow soldering. More preferably, it exhibits a wettability contact angle in the range of ˜120 °. The wettability contact angle as used in the present invention refers to a cylindrical molded body having a diameter of 1 mm and a height of 1 mm made from a powdery soldering composition, placed on a Cu plate, and passed through a reflow furnace at a predetermined temperature. Then, the obtained sample passes through the center point of the solder and is cut together with the Cu plate at a plane perpendicular to the Cu plate, the cut surface is polished, and observed with an SEM, and the JIS C 0050 (1996) “3. It is a value obtained by measuring as the contact angle of the molten solder described in “2 Contact Angle”.

  Further, the soldering composition of the present invention may be in a powder state, a compression-molded solid, or a paste containing a flux depending on the use mode. .

  Furthermore, the soldering composition of the present invention can contain a trace amount of a third metal component. Examples of the third metal component include P, Si, Ge, and Ga. At least one selected from the group can be used.

In the above-described soldering method using the soldering composition of the present invention (hereinafter abbreviated as the soldering method of the present invention), the first metal component is melted. The second metal component diffuses into the molten first metal component. That is, the second metal component does not melt at the soldering temperature. However, since the molten first metal component covers the periphery of the second metal component, the second metal component diffuses into the melt and the alloying progresses, resulting in a uniform composition, a substantially uniform composition or A composition in which a part of the second metal component remains in an island shape without being diffused. By this alloying, an alloy having a higher solidus temperature than that of the soldering composition is formed, and soldering is achieved. In the present invention, “melting” includes not only the state of being completely in a liquid phase but also the case of partially leaving a solid phase.

  A preferred embodiment of the present invention is a soldering method for forming an electronic circuit device including an electronic component mounting substrate and a plurality of electronic components soldered on both sides thereof, and soldering on at least one side is performed by the solder of the present invention. It is carried out according to the attaching method. That is, soldering on one side of the electronic component mounting board may be performed by the soldering method of the present invention, and soldering on the other side may be performed by a soldering method other than the present invention.

  In the soldering method of the present invention, the electronic component is soldered to one surface of the electronic component mounting board by the soldering method of the present invention, and then the solder of the present invention is applied to the opposite surface of the electronic component mounting board. It is preferable to solder an electronic component by an attaching method to form an electronic circuit device including an electronic component mounting substrate and a plurality of electronic components soldered on both sides thereof. In this case, the same soldering composition can be used for each soldering of both surfaces of the electronic component mounting board.

In the soldering method according to the preferred embodiment of the present invention, the reflow soldering is performed at a temperature within the range of 260 to 320 ° C. By this reflow soldering, an Sn-Ag alloy composed of Sn15 to 24.5 mass% and Ag75.5 to 85 mass% is formed. When performing soldering on both sides of the electronic component mounting board according to the soldering method of the present invention, the solidus temperature of the alloy formed by the first reflow soldering is higher than the next reflow soldering temperature. that a high. Therefore, in the next reflow soldering, it is possible to avoid the floating of the electronic component and the decrease in the bonding strength due to the melting of the solder.

  Below, an electronic component is soldered to one side of the electronic component mounting board by the soldering method of the present invention, and then the electronic component is soldered to the opposite surface of the electronic component mounting board by the soldering method of the present invention. A soldering method of the present invention for forming an electronic circuit device including an electronic component mounting substrate and a plurality of electronic components soldered on both sides thereof will be described with reference to FIGS.

  First, as shown in FIG. 1, conductive patterns 2 and 3 are formed on one side of an electronic component mounting substrate 1, and the terminal electrodes 5 of the chip-like electronic component 4 and the conductive patterns 2 and 3 are formed on the conductive patterns 2 and 3, respectively. 6 is a paste-like composition for soldering according to the present invention containing a flux (the first metal component is Sn-3.5Ag fine powder, the second metal component is Ag fine powder, Sn-3. 5Ag: Ag mass ratio 24.9: 75.1) and 7) and 8 are applied. In general, a rosin flux is used as the flux, but the flux is not limited to these and may be a flux of other components. An electronic component mounting substrate 1 shown in FIG. 1 is a double-sided mounting substrate, and a conductive pattern 9 for soldering other electronic components on a surface opposite to the surface on which the conductive patterns 2 and 3 are formed, and 10 is formed.

  Next, the chip-shaped electronic component 4 is placed on the soldering compositions 7 and 8, and passed through a reflow furnace at a predetermined temperature (for example, 270 ° C.), and the soldering compositions 7 and 8 are alloyed. Then, the alloy solders 11 and 12 are formed, and the terminal electrodes 5 and 6 of the electronic component 4 are soldered to the conductive patterns 2 and 3 through the alloy solders 11 and 12, respectively, as shown in FIG.

  As shown in FIGS. 1 and 2, after the terminal electrodes 5 and 6 of the electronic component 4 are soldered to the conductive patterns 2 and 3 on one side of the electronic component mounting substrate 1, respectively, the electronic component mounting substrate 1 is turned upside down. To do. Then, as shown in FIG. 3, the terminal electrodes 14 and 15 of the chip-like electronic component 13 are soldered on the conductive patterns 9 and 10 formed on the opposite surface of the electronic component mounting substrate 1, respectively. A paste-like composition for soldering of the present invention containing a flux at the position to be applied (may be the same composition as the above-mentioned soldering compositions 7 and 8 or a different composition) 16 and 17 are applied.

  Next, the chip-like electronic component 13 is placed on the soldering compositions 16 and 17, and passed through a reflow furnace at a predetermined temperature (for example, 270 ° C.), so that the soldering compositions 16 and 17 are alloyed. Then, the alloy solders 18 and 19 are formed, and the terminal electrodes 14 and 15 of the electronic component 13 are soldered to the conductive patterns 9 and 10 through the alloy solders 18 and 19, respectively, as shown in FIG. The alloy solders 11 and 12 do not melt even when passed through a reflow furnace.

Hereinafter, the present invention will be described in detail based on examples and comparative examples.
Example 1
A printed board was prepared using a paper phenolic resin board or an aluminum board. The first metal component is Sn-3.5Ag alloy (melting point 221 ° C.) fine powder, the second metal component is Ag (melting point 960.5 ° C.) fine powder, and the mass of Sn-3.5Ag: Ag. 80 parts by mass of solder powder having a ratio of 24.9: 75.1 (the solidus temperature of the Sn-76Ag alloy is 480 ° C.), 50% by mass of rosin, 35% by mass of carbitol, and amine hydrohalide A solder paste containing 5 parts by mass of salt and 20 parts by mass of a flux composed of 10% by mass of wax was prepared.

  The solder paste was applied onto the printed circuit board at intervals of 0.25 mm so that the amount of paste applied at each location was 0.5 mg. A reflow oven with a reflow temperature shown in Table 1 below is placed on the solder paste so that both terminals of a C0603 (length 0.6 mm x width 0.3 mm x thickness 0.1 mm) multilayer ceramic capacitor come. The reflow soldering was carried out by passing through the furnace so that the residence time was 10 minutes. The reflow temperature up to 320 ° C. was carried out with a paper phenolic resin substrate, and the reflow temperature over 320 ° C. was carried out with an aluminum substrate. 100 samples were used for each reflow temperature.

  Those in which a bridge was formed between the solders after reflow soldering were regarded as defective, and the number of samples (the number of shorts) in which the bridge was formed was examined visually. The fixing strength was determined by pressing from the side of the chip and measuring the pressing force when the solder was broken. The practically required fixing strength is 10 N or more. The results were as shown in Table 1.

  Furthermore, as a wettability contact angle, a cylindrical shape having a diameter of 1 mm and a height of 1 mm from a powdery soldering composition comprising 24.9% by mass of Sn-3.5Ag fine powder and 75.1% by mass of Ag fine powder. The molded body was placed on a Cu plate, passed through a reflow furnace having a reflow temperature shown in Table 1 so that the residence time was 10 minutes, and the obtained sample was passed through the center point of the solder, Cu Cut along the Cu plate with a plane perpendicular to the plate, polish the cut surface, observe with SEM, and determine the contact angle of the molten solder described in “3.2 Contact Angle” of JIS C 0050 (1996). It was measured. The results were as shown in Table 1.

Comparative Example 1
Instead of the solder paste used in Example 1, the first metal component is Sn-3.5Ag alloy (melting point 221 ° C.) fine powder, the second metal component is Ag (melting point 960 ° C.) fine powder, Sn The mass ratio of −3.5Ag: Ag is 72.5: 27.5 (the solidus temperature of the Sn-30Ag alloy is 221 ° C.), and the solder paste containing the flux used in Example 1 is used. Except for the above, the number of shorts between chips was examined in the same manner as in Example 1, and the adhesion strength and wettability contact angle were measured. The results were as shown in Table 2.

  As is apparent from the data in Table 2, when the solder paste of Comparative Example 1 is used, short-circuit defects are observed even when the reflow temperature is 260 to 300 ° C., and the number of shorts increases when the reflow temperature is higher than that. There were many. On the other hand, as is apparent from the data in Table 1, the soldering composition of the present invention has no short-circuit defects in all measured temperature ranges, sufficient fixing strength, and good wettability. there were.

It is the schematic which shows the 1st step of the double-sided soldering method using the composition for soldering of this invention. It is the schematic which shows the next step of the step shown in FIG. 1 of the double-sided soldering method using the soldering composition of this invention. It is the schematic which shows the next step of the step shown in FIG. 2 of the double-sided soldering method using the soldering composition of this invention. It is the schematic which shows the next step of the step shown in FIG. 3 of the double-sided soldering method using the soldering composition of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic component mounting board 2, 3, 9, 10 Conductive pattern 4, 13 Electronic component 5, 6, 14, 15 Terminal electrode 7, 8, 16, 17 Soldering composition 11, 12, 18, 19 Alloy solder

Claims (3)

Does not contain lead, consists of a first metal component and second metal component, the first metal component is a powder of Sn-3.5Ag alloy, the second metal component is in powder Ag, and the first metal component The relative amount with respect to the second metal component is such that the second metal component diffuses into the molten first metal component during reflow soldering and is alloyed to form Sn15-24.5% by mass and Ag75.5-85% by mass. A composition for soldering, wherein the composition is a relative amount capable of forming a Sn—Ag-based alloy.   The soldering composition according to claim 1, wherein the soldering composition is in a powder state. The soldering composition according to claim 1, wherein the soldering composition is in a paste state further containing a flux .

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