CN1817071A - Reflow soldering method using pb-free solder alloy and hybrid packaging method and structure - Google Patents

Abstract

The invention relates to a method of mixed loading and mounting using Pb-free solder, which is characterized in that it comprises: placing a surface mounting component (2) at least on the top surface of a circuit substrate (1), using Sn-(1-4 )Ag－(0～1)Cu－(7～10)In (unit: mass %) is a reflow soldering process for soldering with a Pb-free solder paste composed of an alloy based on the matrix; inserting the leads of the mounted components (5) or The insertion process of the terminal inserted into the penetration hole on the circuit substrate (1) from the top surface side; the flux coating process; the preheating process; the preheated circuit substrate (1) in the preheating process The bottom surface is brought into contact with the jet (3) of Pb-free solder, and the lead or terminal inserted into the mounted component is reflow-soldered on the circuit board.

Description

Reflow soldering method using Pb-free solder, mixed mounting method and structure

technical field

The present invention relates to a reflow soldering method using a Pb-free solder alloy with low toxicity, a mixed mounting method, and a mixed mounting structure.

Background technique

In the actual operation of soldering electronic components to circuit boards such as organic substrates, there has been a demand to use Pb-free solder alloys with low toxicity.

Regarding the mounting method using this Pb-free solder, there are known as prior art: JP-A-10-166178 (Prior Art 1), JP-A-11-179586 (Prior Art 2), JP-A-11-179586 (Prior Art 2), Publication No. 11-221694 (Prior Art 3), Publication No. 11-354919 (Prior Art 4), Publication No. 2001-168519 (Prior Art 5) and Publication No. 2003-46229 (Prior Art 6) etc.

Conventional Art 1 describes that the Pb-free solder includes a Sn—Ag—Bi based solder or a Sn—Ag—Bi—Cu based solder alloy. Conventional Art 2 describes the connection of protruding Sn—Ag—Bi solder, which is a Pb-free solder, to an electrode on which a Sn—Bi layer is applied. In prior art 3, it is described that on each of the two surfaces composed of the first surface and the second surface of the organic substrate, Sn is the main component and contains 0 to 65% by mass of Bi, 0.5 to 4.0% by mass of Ag, and Cu. Or/and reflow soldering of Pb-free solder with 0 to 3.0% by mass of In in total. Conventional Art 4 describes a technique of cooling the solder at a cooling rate of about 10 to 20° C./s in a method of connecting an electronic component to a circuit board using Bi-containing Pb-free solder. In prior art 5, it is described that the electronic components are surface-connected and mounted on the A side of the substrate by reflow soldering, and then the leads and electrodes of the electronic components inserted from the A side are reflow soldered and mounted on the B side of the substrate by reflow soldering. method, wherein the solder used for reflow soldering used on the A side is composed of Sn-(1.5～3.5wt%)Ag-(0.2～0.8wt%)Cu-(0～4wt%)In-(0～ Pb-free solder composed of 2wt% Bi, and the solder used for reflow soldering on the B side is a Pb-free solder composed of Sn-(0-3.5wt%)Ag-(0.2-0.8wt%)Cu. In prior art 6, it is described that in the mixed mounting method using Pb-free solder, the top surface of the circuit board is cooled, and the re-melting of the solder for surface mount component connection is performed by applying Pb-free solder to prevent surface damage. Mounted parts fall off. Furthermore, Conventional Art 6 also describes the use of Sn-(1-4)Ag-(0-8)Bi-(0-1)Cu (unit: mass %) as a solder alloy for reflow solder paste, and as The reflow solder used Sn-3Ag-0.5Cu or Sn-0.8Ag-57Bi (unit: mass %) close to the eutectic composition.

Contents of the invention

However, recently, in the mixed mounting method using Pb-free solder, it is necessary to use low heat-resistant electronic components such as FPGA (Field Programable Gate Array, Field Programmable Gate Array) whose main body has a heat resistance temperature of 220°C. Reflow soldering to the surface side of the circuit board.

In addition, in the mixed mounting method, it is necessary to reflow solder the above-mentioned low heat-resistant electronic components to the surface side of the circuit board, and then solder the leads of the electronic components inserted from the surface side of the circuit board with Pb-free solder. Reflow soldering. When performing this reflow soldering, it is necessary to prevent the reliability after soldering from being lowered while preventing the above-mentioned low heat resistance electronic components from falling off due to remelting of the reflowed solder.

However, in the above-mentioned prior arts 1 to 6, no sufficient consideration has been given to a mixing method that uses Pb-free solder and satisfies these necessary problems.

An object of the present invention is to solve the above-mentioned problems, and to provide a reflow soldering method for realizing reflow soldering of low heat-resistant electronic components such as FPGAs using a Pb-free solder alloy.

In addition, another object of the present invention is to realize reflow soldering of low-heat-resistant electronic components such as FPGAs, and to provide a Pb-free solder alloy that can maintain the reliability of the connection strength of the reflow soldered part when performing the reflow soldering. The mixed load implementation method and system and the mixed load implementation structure.

In order to achieve the above object, the present invention uses Sn-(1～4)Ag-(0～1) Cu-(7～10)In (unit: mass %) as matrix alloy on the top surface or bottom surface of the circuit substrate A reflow soldering method using a Pb-free solder alloy characterized by soldering of surface mount components with a Pb-free solder paste composed of the composition.

In addition, the present invention is characterized in that a Pb-free plating layer is applied to the leads of the above-mentioned surface mount component. Furthermore, the present invention is characterized in that the above-mentioned Pb-free plating layer is a Sn plating layer or a Sn—Bi plating layer.

In addition, the present invention is a mixed mounting method using Pb-free solder, which is characterized in that it includes surface-mounted components including FPGAs and other low-heat-resistant electronic components (heat-resistant temperature is about 220 ° C or less) at least A low-temperature reflow soldering process in which the top surface of the circuit substrate is soldered with In-added low-melting-point Pb-free solder paste; the insertion of the leads or terminals inserted into the mounted components from the top surface side into the penetration holes formed on the above-mentioned circuit substrate process; after inserting the lead or terminal of the mounted component into the through hole in the insertion process, a flux application process of applying flux to the above-mentioned circuit board; after applying flux to the circuit board in the flux application process, preheating The preheating process of the bottom surface of the circuit substrate; in this preheating process, the bottom surface of the circuit substrate is preheated, and the top surface is cooled while the bottom surface is connected with the Sn-Cu system or Sn-Ag system with high reliability. Jet contact of high melting point Pb-free solder, reflow soldering process of reflow soldering lead wires or terminals inserted into mounted components on circuit boards.

Especially in the present invention, the low-melting-point Pb-free solder paste with In added used in the above-mentioned low-temperature reflow soldering process is based on Sn-Cu system, Sn-Ag system, Sn-Ag-Cu system or Sn-Ag- The system formed by adding In to the Bi system is preferably an alloy based on Sn-(1-4)Ag-(0-1)Cu-(4-10)In (unit: mass %).

The reason for adding 4 to 10% by mass of In to the alloy is that, unlike Bi, In has a high solid solubility to the base alloy Sn used as the solder, and is difficult to precipitate in the solder even when it is cooled from the molten state during soldering to room temperature. In addition, even if it precipitates, it will be finely dispersed in the solder. Like Bi, when the solder is cooled, the solder will be cooled unevenly to have a temperature gradient, and it has the property that segregation to the high temperature side is less likely to occur. If this segregation occurs, the connection strength of the connection portion will be significantly lowered, so it is necessary to completely suppress the occurrence of segregation.

In addition, when reflow soldering surface mount components including the above-mentioned low heat-resistant electronic components (heat-resistant temperature is about 220°C) in a reflow furnace, the heat capacity and infrared reflectance may vary depending on the component. Differently, temperature variation occurs in the circuit board on which the components are mounted. In addition, it is known that this temperature deviation can reach a maximum of 15° C. depending on the circuit board. In addition, the above-mentioned low heat-resistant electronic components (heat-resistant temperature of 220°C) are often small components with small heat capacity, and in many cases, the temperature reaches the highest temperature inside the substrate during reflow soldering. On the other hand, in the position where the solder paste is supplied on the circuit board, such as BGA (Ball Grid Array, ball grid array), there is a position between the component body and the circuit board where the hot air of the reflow furnace does not easily flow. In this case, reflow soldering , the lowest temperature is reached inside the substrate.

That is to say, when the above-mentioned low heat resistance electronic components are reflow soldered on the circuit board, it is necessary to melt the reflow soldering paste at a minimum of 205°C (=220-15), which is necessary in Sn-(1～4)Ag - (0 to 1) Add 7 to 10% by mass of In to the Cu-based solder.

For the above-mentioned reasons, in order to realize the reflow soldering of the above-mentioned low heat-resistant electronic components, completely suppress the occurrence of segregation, and prevent the connection strength of the connection from being significantly reduced, the reflow solder paste is made of Sn-(1～4)Ag-( 0-1) Cu-(7-10)In (unit: mass %)-based alloy.

In addition, in the present invention, the Pb-free solder paste in the above-mentioned low-temperature reflow soldering process is Sn-Cu-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Ag-Bi-based, or one in which In is added. The eutectic composition of the system or a composition close to the eutectic composition. In particular, Sn-3Ag-0.5Cu-xIn (0≤x≤9, unit: mass %) is a Sn-Ag-Cu eutectic composition or a composition close to the eutectic composition, and its melting point is higher than that of existing Sn-37Pb has a high melting point of 183° C., and can be used with high connection reliability even under extreme conditions. In addition, Sn-0.8Ag-57Bi has a eutectic composition or a composition close to the eutectic composition, and can be used with high connection reliability when the use temperature is limited.

Next, in the above-mentioned reflow soldering process, the jet temperature of the Pb-free solder that contacts the bottom surface of the circuit board needs to be in the range of 170°C to 260°C. Because this is the sufficient wetting temperature of the solder to the substrate electrodes.

In addition, the Pb contained in the conventional plating layer in the electrode of the surface mount component is contained in a large amount in another low-temperature eutectic composition precipitated from the solder composition (eutectic composition) of the connection part after reflow soldering. Due to the thermal influence of the molten solder (170°C to 260°C) during soldering, when the solder at the reflow connection part is remelted, the low-temperature eutectic structure is preferentially melted, because this composition is easy to condense in the high-temperature part, which promotes the occurrence of the above-mentioned segregation.

In other words, the electrode plating layer of surface mount components is also desirably composed of Pb-free composition, preferably pure Sn (melting point 232° C.) and other constituent elements of solder alloys for surface mounting. In addition, it is preferable to use a composition in which a small amount of Bi is added to Sn for a device in which whiskers are conspicuous.

In addition, in the above-mentioned reflow soldering process, in order to prevent the above-mentioned low heat-resistant electronic components from falling off due to the remelting of the above-mentioned low-melting-point reflow solder with addition of In, it is preferable to blow a maximum temperature of 50°C (20°C to 50°C) on the top surface of the circuit board. °C range) for cooling with fluid such as nitrogen, the flow rate is about 0.3-1.2m ³ /min (preferably 0.5-1.2m ³ /min), which can expand the upper limit of the allowable melting temperature range of reflow solder. However, in order to suppress the accumulation of solder caused by small-diameter penetration holes or penetration holes for inserting mounting components with large heat capacity when soldering on circuit boards, and sometimes sufficient connection strength cannot be obtained after the solder solidifies, so It is best not to use it at a flow rate significantly exceeding the above (1.2m ³ /min).

In addition, in the above-mentioned reflow soldering process, while blowing a fluid such as nitrogen at a maximum temperature of 50°C (20°C to 50°C) on the top surface of the circuit board to cool it, the jig for heat dissipation is brought into contact with the surface. The lead contact of electronic components can expand the upper limit of the allowable melting temperature range of reflow solder.

As described above, according to the present invention, it is possible to realize reflow soldering of low heat-resistant electronic components such as FPGAs to circuit boards using Pb-free solder alloys.

In addition, according to the present invention, it is possible to prevent the use of Pb-free solder alloys to prevent reflow soldering of surface mount components including FPGAs and other low-heat-resistant electronic components on circuit boards and the use of Pb-free solder alloys to prevent the use of Pb-free solder alloys. Solder adhesion defects that occur when Pb-free is used during reflow soldering on circuit boards, and the effect of maintaining high reliability in mixed mounting can be achieved.

In addition, according to the present invention, in the mixed mounting of surface mount components and insert mount components including low heat-resistant electronic components such as FPGAs using Pb-free solder alloys, due to spraying of molten solder during reflow soldering, The allowable range of flow temperature can be expanded to the high temperature side, so the effect of easy temperature control can be achieved.

Description of drawings

FIG. 1 is an explanatory diagram of a first embodiment of the method of mixing and mounting using Pb-free solder according to the present invention.

FIG. 2 is an explanatory diagram of the second and third examples of the mixed mounting method using Pb-free solder according to the present invention.

Fig. 3 is a diagram showing a state where a heat release jig is mounted (mounted) on a QFP according to a fourth embodiment of the present invention.

FIG. 4 is a diagram showing conditions for cracking of a QFP-LSI connection portion in the first embodiment according to the present invention.

Fig. 5 is a diagram showing conditions for cracking of a QFP-LSI connection part according to the second embodiment of the present invention.

FIG. 6 is a diagram showing conditions for cracking of a QFP-LSI connection portion according to a third embodiment of the present invention.

FIG. 7 is a diagram showing conditions for cracking of a QFP-LSI connection portion according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing conditions for cracking of a QFP-LSI connection portion according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing conditions for cracking of a QFP-LSI connection part according to the sixth embodiment of the present invention.

FIG. 10 is a diagram showing conditions for cracking of a QFP-LSI connection portion according to a seventh embodiment of the present invention.

FIG. 11 is a diagram showing cracking conditions of a QFP-LSI connection portion in a comparative example.

Detailed ways

Embodiments of the present invention will be described in detail using diagrams.

In the present invention, as shown in Figure 1, the surface mount components 2 and 4a of low heat-resistant electronic components (heat-resistant temperature below about 220°C) including FPGA (Field Programable Gate Array, Field Programmable Gate Array) are placed on the The top surface 101 of the circuit board 1 such as an organic substrate is soldered with In-added low-melting point Pb-free solder paste 11, and then the lead 12 inserted into the mounted component 5 is inserted into the through hole from the top surface side of the circuit board 1. etc., and then apply flux to the circuit substrate 1, and then reflow soldering through the Pb-free solder jet 3 from the bottom surface 102 of the circuit substrate 1, so as to realize mixed loading and mounting. When performing reflow soldering, in order to shorten the soldering time to the circuit board 1 , first, the bottom surface 102 of the circuit board 1 is preheated with a preheating device 22 such as a sheath heater. Next, reflow soldering is performed from the bottom surface 102 of the circuit board 1 through the Pb-free solder jet 3 , and both sides of the circuit board 1 are cooled immediately after soldering.

In this way, the low heat-resistant electronic components 2 such as FPGA mounted on the top surface 101 of the circuit board 1 have a smaller heat capacity than other general surface mount components, and the temperature tends to rise in many cases.

Therefore, when reflow soldering is performed using a general reflow furnace, the element main body of the above-mentioned low heat-resistant electronic component 2 often becomes the highest temperature portion in the substrate. In addition, during reflow soldering, when the component body has a BGA (Ball Grid Array, Ball Grid Array) with a structure that can easily control the contact between the solder paste supply part and the hot air, the above-mentioned solder paste supply part is often the lowest temperature part in the substrate. . In any case, the low heat-resistant electronic component 2 such as FPGA is often composed of QFP-LSI, and may be composed of BGA-LSI.

That is to say, the temperature difference between the component body of the above-mentioned low heat-resistant electronic component 2 and the solder paste supply part 11 is not uniform in the circuit board 1 , and can reach a maximum of about 15° C. in a general reflow oven. Therefore, if the temperature of the main body of the low heat-resistant electronic component 2 is kept below 220°C, the temperature of the solder paste supply unit 11 must be kept below 205°C, and even at 205°C, it is necessary to melt the Pb-free reflow solder paste.

Here, as the low-melting-point Pb-free solder paste 11 with In added, even at 205°C, molten Sn-(1-4)Ag-(0-1)Cu-(7-10)In (unit: mass % ) as the base alloy material.

Furthermore, when the above-mentioned low heat resistance electronic component 2 is constituted by BGA, it is preferable that the solder balls have the same composition except for the reflowed solder paste.

In addition, the Pb-free material of the reflow solder jet 3 has a eutectic composition such as a Sn-Cu system, a Sn-Ag system, a Sn-Ag-Cu system, a Sn-Ag-Bi system, or a system in which In is added among them. Or a composition close to the eutectic composition. In particular, Sn-3Ag-0.5Cu-xIn (0≤x≤9, unit: mass %) is a Sn-Ag-Cu eutectic composition or a composition close to the eutectic composition, and its melting point is higher than that of existing Sn-37Pb has a high melting point of 183° C., and can be used with high connection reliability even under extreme conditions. In addition, Sn-0.8Ag-57Bi has a eutectic composition or a composition close to the eutectic composition, and can be used with high connection reliability when the use temperature is limited.

Next, in the above-mentioned reflow soldering process, the jet temperature of the Pb-free solder that contacts the bottom surface of the circuit board needs to be in the range of 170°C to 260°C. Because this is the sufficient wetting temperature of the solder to the substrate electrodes.

In addition, in the above-mentioned flux application step, if necessary, a bending preventing jig made of metal such as Al may be attached to the circuit board 1 . In addition, when mounting a surface mount component on the bottom surface of the circuit board 1 by soldering, a cover (not shown) may be mounted on this portion without soldering.

In addition, during reflow soldering, as shown in FIG. 2 , the top surface 102 of the circuit board 1 is cooled by blowing a fluid such as nitrogen at a maximum temperature of 50° C. (in the range of 20° C. to 50° C.) with the substrate cooling device 6. The flow rate is about 0.3 to 1.2 m ³ /min (preferably 0.5 to 1.2 m ³ /min), so that the upper limit of the allowable melting temperature range of the reflow solder can be expanded. In addition, as shown in FIG. 3, if a metal exothermic jig made of Al, etc. is brought into contact with lead wires of the surface mount electronic component 2, etc., the upper limit of the permissible melting temperature range of the reflow solder can be further expanded.

In this way, in the state where the top surface 101 of the circuit board 1 is cooled by the substrate cooling device 6, even if the upper limit of the allowable melting temperature range of the reflow solder is increased by soldering, the connection of the surface mount components 2 and 4 can be prevented. Part of the fall-off caused by the remelting of the low melting point Pb-free solder paste 11 due to the addition of In.

first embodiment

In the first embodiment, for the circuit substrate 1, a generally widely used Cu washer with a thickness of about 1.6mm, a width of about 350mm, and a length of about 350mm, a thickness of the substrate copper foil of about 18μm, and an inner diameter of about 1mm and about 1.6mm is adopted. , A glass epoxy substrate 1a with penetrating holes formed at a density of about 0.7 pieces/cm ² .

For the surface mount device 2, a 32 mm square QFP-LSI 2a having a lead chip of about 0.5 mm, a lead width of 0.2 mm, and 208 42 alloy leads coated with Sn-10mass%Pb was used.

In addition, on the top surface of the glass epoxy substrate 1a, use 10 kinds of In-containing solder pastes (as shown in Table 1) 11 of Sn-3Ag-0.5Cu-xIn (0≤x≤9, unit: mass %) Conduct 32mm square QFP-LSI2a welding.

Table 1 Solder composition (mass%) Solidus temperature (℃) Liquidus temperature (℃) Sn-3Ag-0.5Cu 217 220 Sn-3Ag-0.5Cu-1In 207 219 Sn-3Ag-0.5Cu-2In 206 218 Sn-3Ag-0.5Cu-3In 205 217 Sn-3Ag-0.5Cu-4In 204 216 Sn-3Ag-0.5Cu-5In 202 215 Sn-3Ag-0.5Cu-6In 200 213 Sn-3Ag-0.5Cu-7In 198 211 Sn-3Ag-0.5Cu-8In 195 210 Sn-3Ag-0.5Cu-9In 193 209

Table 1 shows that when In reaches 7% by mass, the solidus temperature is 198°C, the liquidus temperature is 211°C, and it melts at around 205°C. That is, when the In content is 7% by mass or more, it is possible to reflow-solder low-heat-resistant electronic components (heat-resistant temperature below about 220° C. or less) 2 such as FPGAs to the surface side of the circuit board 1 .

However, when the In content exceeds 10% by mass, segregation occurs when the solder is cooled, and the connection strength of the connection part is significantly lowered, so the In content must be limited to 10% by mass or less.

Then, from the top surface side of the circuit substrate 1 of the substrate sample QFP-LSI2a connected to the 4 connected substrates, insert 6 Sn-10mass%Pb platings with 0.5mm square terminals into the through holes (not shown) of the substrate. Terminal node 5a of 2.54mm chip 6 of (lead) 11a.

The bottom surface 102 of the circuit board 1 is preheated with a sheath heater with a maximum output of 9 kW, and the temperature of the bottom surface 102 of the circuit board 1a at 25°C (room temperature) is heated to a maximum of 118°C and a minimum of 100°C in 1 minute. Then, in the state where the top surface 101 of the circuit board 1 is not cooled by the substrate cooling device 6, Sn-3Ag-0.5Cu (unit: mass %) or Sn-0.8Ag-57Bi (unit: mass %) close to the eutectic composition is used. Mass %) solder jet 3a contacts the bottom surface 102 of the circuit board 1a, and without cooling by the cooling device 6 as shown in FIG. However, at this time, the molten solder in the reflow soldering tank (not shown) is Sn-0.8Ag-57Bi, Sn-0.7Cu, or Sn-3Ag-0.5Cu, and the temperature of the reflowing soldering tank is fixed at 170°C to 260°C. The temperature satisfies several conditions.

Regarding the samples described above, it was observed whether or not cracks occurred in the connection portion of QFP-LSI2a.

Fig. 4 shows the experimental results when the reflow soldering material composition is Sn-3Ag-0.5Cu-xIn (0≤x≤9, unit: mass %) of the present invention, 10 kinds of In-containing solder pastes. FIG. 11 shows experimental results when the reflow soldering material composition is Sn-3Ag-0.5Cu-xBi (0≦x≦8, unit: mass %) of nine kinds of Bi-containing solder pastes as a comparative example.

In each figure, the horizontal axis represents the temperature of the molten solder in the reflow solder tank, and the vertical axis represents the content of Bi and In of the solder used to connect the QFP-LSI. The condition where no cracking occurs is indicated by ○, and the condition where cracking occurs is indicated by The x symbol represents.

In addition, the solid line in each figure can be considered as the boundary between the cracking condition and the non-cracking condition. In addition, in order to compare the experimental results of FIG. 4 with the experimental results of the comparative example of FIG. 11 , the boundaries of FIG. 11 are indicated by dotted lines in FIG. 4 .

As shown in FIG. 4, even if the top surface 101 of the substrate 1a is not cooled, the solder paste 11 used to connect the QFP-LSI2a is defined as the Sn-3Ag-0.5Cu-xIn involved in the present invention. , Compared with the comparative example designated as Sn-3Ag-0.5Cu-xBi, cracking of the connection part is less likely to occur during reflow soldering, and the allowable temperature range of molten solder can be expanded.

That is, it has been found through experiments that adding In to the Sn-Ag-Cu system as in the present invention as the composition of the reflow solder for surface mounting suppresses segregation and falling off of surface mount components during reflow soldering.

In addition, according to the experimental results shown in Fig. 4, it can be found that the temperature of the reflowed molten solder can reach 235°C when the In content is 7% by mass, and the temperature of the reflowed molten solder can reach 230°C when the In content is 8-9% by mass.

2nd embodiment

The difference between the second embodiment and the first embodiment is that during soldering, as shown in FIG. , and its flow rate is about 0.5m ³ /min. In FIG. 5 , the horizontal axis represents the temperature of the molten solder in the reflow solder tank, and the vertical axis represents the In content of the solder used to connect the QFP-LSI. The condition of no cracking is indicated by ○, and the condition of cracking is indicated by x. In addition, the solid line in Fig. 5 can be regarded as the boundary between the cracking condition and the non-cracking condition.

From the experimental results of the second embodiment, it was found that, as shown in FIG. 5 , the upper temperature limit of the reflowed molten solder can be raised by less than 10° C. compared with that of the first embodiment shown in FIG. 4 . In addition, according to the experimental results shown in Figure 5, it can be confirmed that the temperature of the reflowed molten solder can reach 245°C when the In content is 7% by mass, and the temperature of the reflowed molten solder can reach 240°C when the In content is 8% by mass, and the In content is At 9% by mass, the temperature of the reflowed molten solder can reach 235°C.

3rd embodiment

The third embodiment is that in the second embodiment, as shown in FIG. 2 , the top surface 101 of the circuit board 1 is cooled by blowing fluids such as nitrogen at about 20°C to 50°C with the substrate cooling device 6, and the flow rate is approximately 1.2m ³ /min. In FIG. 6, the horizontal axis represents the temperature of the molten solder in the reflow solder tank, and the vertical axis represents the In content of the solder used to connect the QFP-LSI. The condition without cracking is indicated by ○ and the condition of cracking is indicated by ×. In addition, the solid line in Fig. 6 can be regarded as the boundary between the cracking condition and the non-cracking condition.

From the experimental results of the third example, it was found that, as shown in FIG. 6 , the upper limit of the allowable temperature of the reflow molten solder can be increased by about 15° C. compared with that of the first example shown in FIG. 4 . In addition, according to the experimental results shown in Figure 6, it can be found that the temperature of the reflowed molten solder can reach 250°C when the In content is 7% by mass, and the temperature of the reflowed molten solder can reach 245°C when the In content is 8% by mass, and the In content is At 9% by mass, the temperature of the reflowed molten solder can reach 240°C.

Based on the above results, if the flow rate of blowing nitrogen or the like is increased to 1.2m ³ /min, even if the In content of the reflow solder used for surface mount components is increased by 7% to 9%, it is possible to use 240°C to 250°C Sn-Ag-Cu molten solder for reflow soldering.

4th embodiment

In the fourth embodiment, similar to the second and third embodiments, when soldering is performed, the substrate cooling device 6 is operated, and the connection of the surface mount device (32mm square QFP-LSI) 2 is further reflow soldered. The heat dissipation jig 7 with a square frame made of metal such as aluminum is mounted on the top, and the heat dissipation jig 7 is brought into contact with the lead wire of the surface mount component 2, thereby cooling the top surface 101 of the circuit board 1 and improving the suppression during reflow soldering. The effect of segregation and shedding of surface mounted components. In this case, the reflow molten solder is Sn-0.7Cu or Sn-3Ag-0.5Cu, and the temperature of the fixed reflow solder tank satisfies several conditions in order to keep the temperature at 250°C to 280°C.

In FIG. 7 , the horizontal axis represents the temperature of the molten solder in the reflow solder tank, the vertical axis represents the In content of the solder used to connect the QFP-LSI, the condition without cracking is indicated by ○, and the condition of cracking is indicated by x. In addition, the solid line in Fig. 6 can be regarded as the boundary between the cracking condition and the non-cracking condition.

From the experimental results of the fourth embodiment, it was found that, as shown in FIG. 7 , the upper limit of the allowable temperature of the reflowed molten solder can be increased by about 20° C. compared with that of the first embodiment shown in FIG. 4 . In addition, according to the experimental results shown in Fig. 7, it can be found that the temperature of the reflowed molten solder can reach 260°C when the In content is 7% by mass, and the temperature of the reflowed molten solder can reach 250°C when the In content is 8-9% by mass.

Based on the above results, cooling the top surface of the substrate with a nitrogen blowing rate of about 1.2m ³ /min, even if the content of In added to the reflow solder for surface mount components is about 9% by mass, when using an exothermic jig, Reflow soldering can also be performed using 250°C Sn-Ag-Cu molten solder or the like. That is, according to the fourth embodiment, when reflow soldering is performed using Sn-Ag-Cu molten solder at 250°C or the like, the content of In that can be added to the reflow solder for surface mount components can be increased to 9% by mass Left and right, it is easy to make it adequately correspond to low heat resistance electronic components.

fifth embodiment

In the fifth embodiment, in the first embodiment, the effect of suppressing segregation and falling off of the surface mount device during reflow soldering can be enhanced by making the lead plating layer of the surface mount device subjected to reflow soldering free of Pb.

However, the molten solder in the reflow solder tank (not shown) used at this time is Sn-0.8Ag-57Bi, Sn-0.7Cu, or Sn-3Ag-0.5Cu (unit: mass %) close to the eutectic composition. Its temperature is between 235°C and 280°C, and the temperature of the fixed reflow solder tank satisfies several conditions.

Regarding the samples described above, it was observed whether or not cracks occurred in the connection portion of QFP-LSI2a.

8 and 9 respectively show the experimental results of the Sn-3% by mass Bi plating layer and the Sn plating layer of the fifth embodiment. The horizontal axis of Figure 8 and Figure 9 represents the temperature of the molten solder in the reflow soldering tank, the vertical axis represents the In content of the solder used to connect QFP-LSI, the condition without cracking is indicated by ○, and the condition of cracking is indicated by x . In addition, the solid line in each figure can be considered as the boundary between the cracking condition and the non-cracking condition.

In addition, in order to compare with the experimental results of FIG. 4 (using Sn-10Pb plating), the boundary of FIG. 4 is indicated by a dotted line in FIG. 8 . In addition, in order to compare with the experimental results of FIG. 8 (using Sn-3Bi plating), the boundary of FIG. 8 is indicated by a dotted line in FIG. 9 .

From the above results, it can be seen that when Sn-3Bi plating is used (Fig. 8), in the case of reflow soldering with Sn-Ag-Cu molten solder at 250°C, etc., In the solder used for surface mount components, the In The content is about 8% by mass. In addition, in the case of using Sn plating (Fig. 9), in the case of reflow soldering with Sn-Ag-Cu molten solder at 250°C, etc., the amount of In that can be added to the solder for surface mount components is 9% by mass. about. However, it has been found that when reflow soldering is performed with molten Sn-Ag-Cu solder at 260° C., the content of In that can be added to the solder for surface mount components is about 5% by mass.

As mentioned above, according to the fifth embodiment in which the lead plating layer of the surface mount component is made Pb-free, as in the first embodiment, the substrate cooling device 6 is not used for cooling, and the content of In that can be added to the reflow soldering material can be 8 to 50%. About 9%, it is easy to make it adequately correspond to low heat resistance electronic components.

sixth embodiment

In the sixth embodiment, in the fourth embodiment, the effect of suppressing segregation and falling off of the surface mount device during reflow soldering can be enhanced by making the lead plating layer of the surface mount device subjected to reflow soldering free of Pb.

However, the molten solder in the reflow solder tank (not shown) used at this time is Sn-0.7Cu or Sn-3Ag-0.5Cu (unit: mass %) close to the eutectic composition. ℃, the temperature of the fixed reflow soldering tank satisfies several conditions.

Regarding the samples described above, it was observed whether or not cracks occurred in the connection portion of QFP-LSI2a.

Fig. 10 shows the experimental results of the sixth example. 10, the horizontal axis represents the temperature of the molten solder in the reflow soldering tank, and the vertical axis represents the In content of the solder used to connect QFP-LSI. The condition without cracking is indicated by ○ and the condition of cracking is indicated by x. In addition, the solid line in Fig. 10 can be regarded as the boundary between the cracking condition and the non-cracking condition. In addition, in order to compare with the experimental results of FIG. 9 (using Sn plating, neither cooling the top surface of the substrate nor using heat dissipation fixtures), the boundary of FIG. 9 is indicated by a dotted line in FIG. 10 .

As shown in FIG. 10, according to the sixth embodiment, in the case of reflow soldering with Sn-Ag-Cu molten solder at two temperatures of 250°C and 260°C, the amount of In that can be added to the solder for surface mount components The content is all about 9% by mass, and as a result, it is easy to sufficiently cope with low heat-resistant electronic components.

Possibility of industrial use

The invention can realize the soldering of the low heat-resistant electronic components such as FPGA to the circuit board by using the Pb-free solder alloy.

Claims (17)

1. reflow soldering method that uses Pb free solder alloy is characterized in that: use in the end face of circuit substrate or bottom surface that (unit: quality %) the no Pb soldering paste of forming as matrix alloy welds surface real dress element by Sn-(1～4)-Ag-(0～1) Cu-(7～10).

2. the reflow soldering method of use Pb free solder alloy as claimed in claim 1 is characterized in that: apply no Pb coating on the lead-in wire of described surface real dress element.

3. the reflow soldering method of use Pb free solder alloy as claimed in claim 2 is characterized in that: described no Pb coating is Sn coating or Sn-Bi coating.

4. one kind is used mixing of Pb free solder alloy to carry mounting method, and it is characterized in that: it comprises:

Surface real dress element at least at the end face of circuit substrate, is used (the unit: the low temperature reflux welding sequence that welds of the no Pb soldering paste of forming for matrix alloy quality %) by Sn-(1～4) Ag-(0～1) Cu-(7～10) In;

The lead-in wire of real dress element or terminal insert the through hole that described circuit substrate wears from end face one side insertion operation will be inserted;

After in this inserts operation, will inserting the lead-in wire or terminal insertion through hole of real dress element, be coated with the flux operation to described circuit substrate brushing flux;

Be coated with in the flux operation after circuit substrate is coated with flux the preheating procedure of this circuit substrate bottom surface of preheating at this;

Make preheating in this preheating procedure the bottom surface of circuit substrate, contact with the jet flow of Pb-free solder, will insert the lead-in wire of real dress element or terminal carries out reflow soldering on circuit substrate reflow soldering operation.

5. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 4, it is characterized in that: in described reflow soldering operation, apply no Pb coating on the lead-in wire of described surface real dress element.

6. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 5, and it is characterized in that: described no Pb coating is Sn coating or Sn-Bi coating.

7. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 4, it is characterized in that: in described reflow soldering operation, described Pb-free solder is Sn-Cu system, Sn-Ag system, Sn-Ag-Cu system, Sn-Ag-Bi system or adds In become the eutectic composition that is or the composition approaching with this eutectic composition in the middle of these.

8. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 5, it is characterized in that: in described reflow soldering operation, described Pb-free solder is Sn-Cu system, Sn-Ag system, Sn-Ag-Cu system, Sn-Ag-Bi system or adds In become the eutectic composition that is or the composition approaching with this eutectic composition in the middle of these.

9. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 7, and it is characterized in that: the jet flow temperature of described Pb-free solder is in 170 ℃～260 ℃ scope.

10. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 8, and it is characterized in that: the jet flow temperature of described Pb-free solder is in 170 ℃～260 ℃ scope.

11. use Pb free solder alloy as claimed in claim 7 mix to carry a mounting method, it is characterized in that: in the operation of described reflow soldering, the end face of described circuit substrate is blowed 50 ℃ or following fluid cool off.

12. use Pb free solder alloy as claimed in claim 8 mix to carry a mounting method, it is characterized in that: in the operation of described reflow soldering, the end face of described circuit substrate is blowed 50 ℃ or following fluid cool off.

13. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 11, it is characterized in that: in the operation of described reflow soldering, the flow of described fluid is 0.3～1.2m ³/ minute.

14. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 12, it is characterized in that: in the operation of described reflow soldering, the flow of described fluid is 0.3～1.2m ³/ minute.

15. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 11, it is characterized in that: in the operation of described reflow soldering, use the heat release jig to contact installation with the connecting portion of surface real dress element.

16. mounting method is carried in mixing of use Pb free solder alloy as claimed in claim 12, it is characterized in that: in the operation of described reflow soldering, use the heat release jig to contact installation with the connecting portion of surface real dress element.

17. use mixing of Pb free solder alloy to carry the mixed year packaging structure body that mixes that carries real dress of mounting method as claim 4 or 5 or 7 or 8 described employings.

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