KR20060052719A - Reflow soldering method using pb-free solder alloy and hybrid packaging method and structure - Google Patents

Abstract

A hybrid packaging method employing a Pb- free solder alloy characterized by comprising a step for performing reflow soldering of a surface mounting component (2) onto at least the upper surface of a circuit board (1) using Pb-free solder paste of Sn-(1- 4)Ag-(0-1)Cu-(7-10)In (unit: mass%) based alloy, a step for inserting the lead or terminal of an insertion mounting component (5) into a through hole made through the circuit board (1) from the upper surface side, a step for applying flux, a step for preheating, and a step for flow- soldering the lead or terminal of an insertion mounting component to the circuit board by spraying a jet flow (3) of Pb-free solder to the lower surface of the circuit board (1) which is preheated in the preheating step.

Description

REFLOW SOLDERING METHOD USING Pb-FREE SOLDER ALLOY AND HYBRID PACKAGING METHOD AND STRUCTURE}

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

When soldering and installing electronic components with circuit boards, such as an organic board | substrate, there exists a demand which uses the Pb free solder alloy with low toxicity.

As a prior art regarding the mounting method using this Pb-free solder, Unexamined-Japanese-Patent No. 10-166178 (Prior Art 1), Unexamined-Japanese-Patent No. 11-179586 (Prior Art 2), Japanese Patent Laid-Open No. 11-221694 Japanese Patent Application Laid-Open No. 11 (Prior Art 3), Japanese Patent Application Laid-Open No. 11-354919 (Prior Art 4), Japanese Patent Application Laid-Open No. 2001-168519 (Prior Art 5) and Japanese Patent Publication No. 2003-46229 (Prior Art 6) Etc. are known.

Prior art 1 describes Sn-Ag-Bi-based solder or Sn-Ag-Bi-Cu-based solder alloy as Pb-free solder. Prior art 2 describes connecting Sn-Ag-Bi-based solder, which is a strong Pb-free solder, with an electrode having a Sn-Bi-based layer on its surface. In the prior art 3, the electronic component has Sn as a main component on each of both surfaces consisting of the first and second surfaces of the organic substrate, 0 to 65 mass% of Bi, 0.5 to 4.0 mass% of Ag, Cu or / and In It is described to reflow solder by Pb-free solder containing 0-3.0 mass% in total. Prior art 4 describes a method of connecting an electronic component and a circuit board using an Fb-free solder containing Bi, wherein the solder is cooled at a cooling rate of about 10 to 20 ° C / s. In the prior art 5, the electronic component is surface-connected by reflow soldering on the A side of the substrate, and the lead of the electronic component inserted from the A-side side by flow soldering on the B side of the substrate is flow-flow soldered onto the electrode. In the method, the solder used for reflow soldering on the surface A is Sn- (1.5 to 3.5 wt%) Ag- (0.2 to 0.8 wt%) Cu- (0 to 4 wt%) In- (0 to 2 wt% ) Pb-free solder composed of Bi and Pb-free solder composed of Sn- (0 to 3.5 wt%) Ag- (0.2 to 0.8 wt%) Cu. It is described. In the conventional technique (6), in the method of mixed mounting using Pb-free solder, the upper surface of the circuit board is cooled and flow soldered to prevent peeling of the surface mount component due to remelting of the solder of the connection portion of the surface mount component. Is described. In addition, the prior art 6 uses Sn- (1-4) Ag- (0-8) Bi- (0-1) Cu (unit: mass%) as a solder alloy of a reflow solder paste, and processes as flow solder (Iii) It is described to use Sn-3Ag-0.5Cu or Sn-0.8Ag-57Bi (unit: mass%) close to the composition.

By the way, in the recent hybrid mounting method using Pb-free solder, it is necessary to reflow solder a low-heat-resistance electronic component such as an FPGA (field programmable gate array) whose heat resistance temperature of the component main body is 220 ° C to the surface side of the circuit board. It has been done.

In the mixed mounting method, the low heat-resistant electronic component needs to be reflow soldered to the surface side of the circuit board and flow soldered to the lead of the electronic component inserted from the surface side of the circuit board using Pb-free solder. . In this flow soldering, the reflow solder needs to be remelted to prevent peeling of the low heat-resistant electronic component and not to deteriorate the reliability after solder connection.

However, the above-mentioned prior arts 1 to 6 have not sufficiently considered a mixed mounting method that satisfies these necessary problems by using Pb-free solder.

An object of the present invention is to provide a reflow soldering method using a Pb-free solder alloy that realizes reflow soldering of low heat resistance electronic components such as FPGAs (field programmable gate arrays).

In addition, another object of the present invention is to realize a reflow soldering of low-heat-resistance electronic components such as FPGAs, and to provide a mixed mounting method using a Pb-free solder alloy to maintain the reliability of the connection strength of the reflow soldering portion during flow soldering. And a system and a mixed mounting structure.

In order to achieve the above object, the present invention provides a surface-mounted component to Sn- (1 to 4) Ag- (0 to 1) Cu- (7 to 10) In (unit: mass%) on the upper or lower surface of the circuit board. A reflow soldering method using a Pb-free solder alloy, wherein soldering is performed using a Pb-free solder paste made of a base alloy.

The present invention is also characterized in that Pb pre-plating is performed on the lead of the surface mount component. In addition, the present invention is characterized in that the Pb pre-plating, Sn plating or Sn-Bi plating.

In addition, the present invention provides a low-temperature reflow in which surface-mount components including low-heat-resistant electronic components such as FPGAs (heat resistance temperature of about 220 ° C. or less) are soldered to at least an upper surface of a circuit board using low melting point Pb-free solder paste. A soldering step, an inserting step of inserting a lead or terminal of an insert mounting part from an upper surface side into a through hole drilled in the circuit board, and inserting a lead or terminal of an inserting mounting part into a through hole in the inserting step, and then A flux coating step of applying flux to the substrate, a preheating step of preheating the lower surface of the circuit board after applying the flux to the circuit board in the flux applying step, and a circuit of preheating the lower surface of the preheating step While cooling the upper surface of the substrate, a high melting point Pb-free solder such as Sn-Cu or Sn-Ag A mixed mounting method using Pb-free solder, comprising a flow soldering step in which a jet flow is brought into contact and a lead or terminal of an inserted mounting component is flow soldered to a circuit board.

In particular, the present invention provides the low-melting-point Pb-free solder paste used in the low-temperature reflow soldering step as Sn-Cu, Sn-Ag, Sn-Ag-Cu or Sn-Ag-Bi. It is an alloy based on the addition, Preferably it is Sn- (1-4) Ag- (0-1) Cu- (4-10) In (unit: mass%).

The reason for adding In (4 to 10% by mass) to the alloy is that, unlike Bi, In has a high solid meltability with respect to Sn as the base metal of the solder, and precipitates in the solder even when cooled to room temperature from the molten state during soldering. it's difficult. This is because segregation into the solder is finely dispersed in the solder even when it is precipitated, so that segregation to the high temperature side is unlikely to occur if the solder does not uniformly cool during the cooling of the solder like Bi and has a temperature gradient. If segregation occurs, in order to significantly lower the connection strength of the connection portion, it is necessary to completely suppress the occurrence of segregation.

In addition, when reflow soldering a surface-mounted component including the low heat-resistant electronic component (a heat-resistant temperature of about 220 ° C.) using a reflow furnace, the components of heat capacity, reflectance of infrared rays, etc. are different for each component. Temperature fluctuations occur in the circuit board on which is mounted. In addition, it turns out that this temperature fluctuation may be at most 15 degreeC by a circuit board. In addition, the low heat resistance electronic component (heat resistance temperature of 220 ° C.) is a small one having a small heat capacity, and in most cases, reaches the highest temperature in the substrate during reflow soldering. On the other hand, some of the places where solder paste is supplied on the circuit board include a place where hot air to reflow is hard to flow between the main body of the component and the circuit board, such as a ball grid array (BGA). It becomes the minimum temperature in the inside.

Therefore, when reflow soldering the said low heat resistance electronic component to a circuit board, it is necessary to melt reflow solder paste in the vicinity of 205 degreeC (= 220-15) minimum, and this is Sn- (1-4) Ag- Addition of about 7 to 10 mass% of In to the (0 to 1) Cu-based solder is necessary.

For the reason explained above, in order to realize reflow soldering of the said low heat-resistant electronic component as a reflow solder paste, and to prevent generation of segregation completely and to reduce the connection strength of a connection part notably, Sn- (1-4) ) An alloy based on Ag- (0 to 1) Cu- (7 to 10) In (unit: mass%).

In the present flow soldering step, the Pb-free solder paste includes Sn-Cu, Sn-Ag, Sn-Ag-Cu, Sn-Ag-Bi, or a system in which In is added thereto. It is a process composition or a composition close to the said process composition. In particular, Sn-3Ag-0.5Cu-xIn (0 ≦ x ≦ 9, unit: mass%) is a Sn-Ag-Cu-based process composition or a composition close to the process composition, and is more than the melting point of 183 ° C of conventional Sn-37Pb. It has a high melting point and can be used with high reliability in connection with extreme conditions. Sn-0.8Ag-57Bi is a process composition or a composition close to the process composition, and can be used with high reliability of connection when the use temperature is limited and used.

And in the said flow soldering process, it is required that the temperature of the jet flow of Pb-free solder which contacts the lower surface of a circuit board exists in the range of 170 degreeC-260 degreeC. This is because the solder is sufficiently wetted with respect to the substrate electrode.

Moreover, Pb contained in the conventional plating in the electrode of a surface mounting component contains a large amount of components which produce the other low-temperature process composition largely deviated from the solder composition (process composition) of the connection part after reflow soldering, and flow Due to the thermal effects of the molten solder (170 ° C. to 260 ° C.) at the time of soldering, this low temperature process composition preferentially melts when reflowing the solder in the reflow connection, and this composition tends to be concentrated in the high temperature portion. Promotes development

Therefore, it is preferable to make the plating of the electrode of a surface mounting component into Pb free composition, and as a composition, it is good to set it as the structural element of the solder alloy used for surface mounting, such as pure Sn (melting point 232 degreeC). In addition, it is said that it is good to use the thing which added the trace amount Bi to Sn about the component which generate | occur | produces the whisker (whisker crystal) remarkably.

In addition, the present invention is 50 ℃ or less (20 ℃ to 50 to the upper surface of the circuit board in the flow soldering process, in order to prevent the low melting point reflow solder to re-melt the low-heat-resistant electronic components in the flow soldering process) And cooling by blowing a fluid such as nitrogen in the range of (° C.) at about 0.3 to 1.2 m 3 / min (preferably about 0.5 to 1.2 m 3 / min) to cool the upper limit of the allowable melting temperature range of the flow solder. It is preferable because it can widen. However, the flow rate (1.2 m3) may not be obtained after solder solidification by suppressing the rise of the solder to the through hole into which the small diameter through-hole and the large-capacity insertion component are inserted when flow soldering to the circuit board. / Min) is preferably not used significantly.

In addition, in the flow soldering step, the present invention provides a heat dissipating jig to a lead of a surface mounted electronic component while cooling a liquid such as nitrogen at 50 ° C. or lower (range of 20 ° C. to 50 ° C.) with respect to the surface of the circuit board. By contacting the upper limit of the allowable melting temperature range of the flow solder can be widened.

As described above, according to the present invention, reflow soldering of a low heat-resistant electronic component such as an FPGA to a circuit board can be achieved by using a Pb-free solder alloy.

In addition, according to the present invention, reflow soldering to a circuit board of a surface-mount component including a low heat-resistant electronic component such as an FPGA and flow soldering to a circuit board for an insert-mount component or the like are performed using a Pb-free solder alloy and Pb is used. It has the effect of preventing the solder defect which arises with freeization, and realizing the mixed mounting which maintained high reliability.

Further, according to the present invention, in a mixed package such as a surface mount component and an insertion mount component including a low heat resistance electronic component such as an FPGA using a Pb-free solder alloy, the temperature allowable range of the jet flow of the molten solder during flow soldering Since it can be extended to the high temperature side, it becomes easy to control temperature.

1 is a view for explaining a first embodiment of a mixed mounting method using Pb-free solder according to the present invention.

Fig. 2 is a view for explaining the second and third embodiments 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 dissipation jig is attached (mounted) to a QFP which is a fourth embodiment according to the present invention.

Fig. 4 is a diagram showing the QFP-LSI connection part breaking condition in the first embodiment according to the present invention.

Fig. 5 is a view showing the QFP-LSI connection part breaking condition in the second embodiment according to the present invention.

Fig. 6 is a diagram showing the QFP-LSI connection part breaking condition in the third embodiment of the present invention.

Fig. 7 is a diagram showing the QFP-LSI connection part breaking condition in the fourth embodiment according to the present invention.

Fig. 8 is a diagram showing QFP-LSI connection part breaking conditions in the fifth embodiment of the present invention.

Fig. 9 is a view showing the QFP-LSI connection part breaking condition in the sixth embodiment of the present invention.

Fig. 10 is a diagram showing the QFP-LSI connection part breaking condition in the seventh embodiment of the present invention.

Fig. 11 is a view showing QFP-LSI connection break conditions in the comparative example.

EMBODIMENT OF THE INVENTION Embodiment of this invention is described in detail using drawing.

As shown in Fig. 1, the present invention provides circuit boards, such as organic substrates, for surface-mounting components 2, 4a containing low heat-resistant electronic components (heat resistance temperature of about 220 캜 or less) such as FPGA (field programmable gate array). In is soldered to the upper surface 101 of (1) using the low melting point Pb-free solder paste 11, and thereafter, the lead of the mounting component 5 is inserted into the through hole or the like from the upper surface side of the circuit board 1. (12) is inserted therein, and then flux is applied to the circuit board 1, and then flow soldered by the Pb-free molten solder jet flow 3 from the lower surface 102 of the circuit board 1 It's about mixing things up. At the time of flow soldering, in order to shorten the soldering time to the circuit board 1, first, the lower surface 102 of the circuit board 1 is preheated by the preheater 22, such as a sheath heater. After that, flow soldering is performed by the Pb-free molten solder jet flow 3 from the lower surface 102 of the circuit board 1, and both surfaces of the circuit board 1 are cooled immediately after soldering.

As described above, the low heat resistance electronic component 2 such as the FPGA mounted on the upper surface 101 of the circuit board 1 generally has a smaller heat capacity and a higher temperature tendency than the other surface mount electronic components.

From this, in a general reflow furnace, the component main body of the said low heat resistance electronic component 2 will become the highest temperature part in a board | substrate at the time of reflow soldering. In addition, in the case of a ball grid array (BGA) or the like having a structure in which the component body easily suppresses the hot air from coming into contact with the solder paste supply portion during reflow soldering, the solder paste supply portion often becomes the lowest temperature portion in the substrate. As a result, low heat-resistant electronic components 2 such as FPGAs are often composed of QFP-LSI, and may be composed of BGA-LSI.

Therefore, the temperature difference between the component main body of the low heat resistance electronic component 2 and the solder paste supply part 11 becomes a temperature fluctuation in the circuit board 1, and becomes a maximum of about 15 degreeC in a normal reflow furnace. For this reason, when the component main body of the said low heat resistance electronic component 2 is made into 220 degrees C or less, the solder paste supply part 11 will necessarily be 205 degrees C or less, and Pb-free reflow solder paste which melt | dissolves also in 205 degreeC is required. Become.

Therefore, as the In, the low melting point Pb-free solder paste 11 is based on Sn- (1 to 4) Ag- (0 to 1) Cu- (7 to 10) In (unit: mass%) that melts at 205 ° C. It is to what made alloy material to say.

In the case where the low heat resistance electronic component 2 is made of BGA, it is desirable to have the same composition as well as the reflow solder paste.

Moreover, as Pb-free material of the flow solder jet flow 3, process composition, such as Sn-Cu system, Sn-Ag system, Sn-Ag-Cu system, Sn-Ag-Bi system, or the system which In added to these, etc. Or a composition close to the process composition. In particular, Sn-3Ag-0.5Cu-xIn (0 ≦ x ≦ 9, unit: mass%) is a Sn-Ag-Cu-based process composition or a composition close to the process composition, and is more than the melting point of 183 ° C of conventional Sn-37Pb. It has a high melting point and can be used with high reliability in connection with extreme conditions. Sn-0.8Ag-57Bi is a process composition or a composition close to the process composition, and can be used with high reliability of connection when the use temperature is limited and used.

And in the said flow soldering process, it is required that the temperature of the jet flow of Pb-free solder which contacts the lower surface of a circuit board exists in the range of 170 degreeC-260 degreeC. This is because the solder is sufficiently wetted with respect to the substrate electrode.

In addition, before the flux coating step, a metal warpage preventing jig such as Al may be attached to the circuit board 1 as necessary. In addition, when the surface mounting component is mounted on the lower surface of the circuit board 1 by reflow soldering, it is also possible to attach a cover (not shown) to this portion to prevent the flow solder from sticking.

In addition, when flow soldering, as shown in FIG. 2, the upper surface 102 of the circuit board 1 is a fluid such as nitrogen at 50 ° C. or less (range of 20 ° C. to 50 ° C.) in the substrate cooling device 6. Is cooled at a flow rate of approximately 0.3 to 1.2 m 3 / min (preferably 0.5 to 1.2 m 3 / min) to allow the upper limit of the allowable melting temperature range of the flow solder to be widened. Further, when the heat dissipation jig of a metal such as aluminum is brought into contact with the lead of the surface mount electronic component 2, as shown in Fig. 3, the upper limit of the allowable melting temperature range of the flow solder can be further increased.

In this way, by performing flow soldering in the state where the upper surface 101 of the circuit board 1 is cooled in the substrate cooling apparatus 6, even if the upper limit of the melting temperature range of the flow solder is widened, the surface mounting components 2 and 4 It is possible to prevent the In from being peeled off by the re-melting of the low melting point Pb-free solder paste 11 at the connection portion of.

[First Embodiment]

The first embodiment is a circuit board 1, which is generally used in a thickness of about 1.6 mm, a length of about 350 mm, a width of about 350 mm, a thickness of about 18 μm of copper foil on a substrate surface, and an inner diameter of about 1 mm. A glass epoxy substrate 1a having a Cu pad diameter of about 1.6 mm and a through hole formed at a density of about 0.7 pieces / cm 2 was used.

As the surface mounting component 2, a 32 mm square QFP-LSI 2a having 208 42 alloy leads with a lead pitch of about 0.5 mm, a lead width of about 0.2 mm, and Sn-10 mass% Pb plating was used.

Then, on the upper surface of the glass epoxy substrate 1a, 32 mm each QFP-LSI 2a was formed of 10 kinds of In-containing solder pastes of Sn-3Ag-0.5Cu-xIn (0 ≦ x ≦ 9, unit: mass%). The details are shown in the following Table 1) (11) to perform reflow soldering.

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

As apparent from Table 1, when In is 7% by mass, the solidus temperature is 198 ° C, the liquidus temperature is 211 ° C, and is melted at around 205 ° C. Therefore, when In is contained 7 mass% or more, it becomes possible to reflow soldering the low heat-resistant electronic component (heat resistance temperature of about 220 degreeC or less) 2, such as FPGA, to the surface side of the circuit board 1. As shown in FIG.

However, when In contains more than 10 mass%, segregation will occur at the time of cooling of solder, and the connection strength of a connection part will fall remarkably, Therefore, content of In needs to be 10 mass% or less.

Next, Sn-10 mass% Pb plating was performed from the upper surface side of the circuit board 1 to which four QFP-LSIs 2a of this board | substrate sample were connected to the through-hole of a board | substrate (not shown). Six 2.54 mm pitch 6-terminal connectors 5a each having a 0.5 mm square terminal (lead) 11a were inserted.

Next, preheating using a sheath heater with a maximum output of 9 kW is performed on the lower surface 102 of the circuit board 1, and the temperature of the lower surface 102 of the circuit board 1a at 25 ° C (room temperature) for 1 minute. Was made into the highest part 118 degreeC and the lowest part 100 degreeC. Subsequently, Sn-3Ag-0.5Cu (unit: mass%) or Sn-0.8Ag-57Bi (near by mass) close to the process composition without cooling the upper surface 101 of the circuit board 1 in the substrate cooling device 6 thereafter. Unit: mass%) Solder jet flow 3a is brought into contact with the lower surface 102 of the substrate 1a and is cooled by the substrate cooling device 6, as shown in FIG. The board | substrate sample was produced toward the soldering of (5a). At this time, the molten solder of the flow solder tank (not shown) is Sn-0.8Ag-57Bi, Sn-0.7Cu or Sn-3Ag-0.5Cu, and the flow solder tank has a temperature of 170 to 260 캜. The temperature was fixed at various conditions.

In the sample described above, it was observed whether or not fracture occurred in the connection portion of the QFP-LSI 2a.

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

Also in each figure, the temperature of the molten solder of a flow solder tank on the horizontal axis was taken, Bi and In content of the solder used for connection of QFP-LSI to the vertical axis | shaft were taken, the conditions which did not produce breakage were shown by (circle), and the conditions which broke | broken were shown by x table.

In addition, the solid line in each figure is a line considered as a boundary of the condition which a break takes place and the condition which does not occur. In addition, in order to compare the experimental result concerning this invention of FIG. 4 with the experimental result of the comparative example of FIG. 11, the boundary of FIG. 11 is shown with the dotted line in FIG.

As shown in Fig. 4, the solder paste 11 used for the connection of the QFP-LSI 2a is Sn-3Ag-0.5Cu- according to the present invention even in the experimental result of not cooling the upper surface 101 of the substrate 1a. By using xIn, it was found that the breakage of the connection part at the time of flow soldering was less likely to occur compared to the comparative example of Sn-3Ag-0.5Cu-xBi, and the allowable temperature range of the molten solder could be widened.

That is, the experiment confirmed that segregation peeling of the surface mounting component at the time of flow soldering can be suppressed by adding In to Sn-Ag-Cu system as a surface mount reflow solder composition like this invention.

Moreover, according to the experimental result shown in FIG. 4, when the content of In is 7 mass%, the temperature of a flow molten solder is 235 degreeC, and when the content of In is 8-9 mass%, the temperature of a flow melt solder is 230 degreeC. I could confirm that I could.

Second Embodiment

In the second embodiment, the difference from the first embodiment is that at the time of flow soldering, as shown in Fig. 2, the upper surface 101 of the circuit board 1 is moved from 20 DEG C to 50 in the substrate cooling apparatus 6. This is a point where a fluid such as nitrogen at a temperature of about ° C. is sprayed at a flow rate of approximately 0.5 m 3 / min and cooled. 5 shows the temperature of the molten solder of the flow solder bath on the horizontal axis, the In content of the solder used to connect the QFP-LSI to the vertical axis, the conditions where no break occurred, and the conditions where the break occurred are represented by the X table. In addition, the solid line in FIG. 5 is a line considered to be a boundary between the condition which breaks and a condition which does not occur.

According to the experimental results of the second embodiment, as shown in FIG. 5, it was confirmed that the upper limit of the temperature of the flow melt solder may be increased by about 10 ° C. as compared with the first embodiment shown in FIG. 4. According to the experimental results shown in Fig. 5, when the content of In is 7% by mass, the temperature of the flow molten solder is up to 245 ° C, and when the content of In is 8% by mass, the temperature of the flow molten solder is 240 ° C. When content of is 9 mass%, it was confirmed that the temperature of flow melt solder can be made to 235 degreeC.

Third Embodiment

In the second embodiment, in the second embodiment, as shown in FIG. 2, the upper surface 101 of the circuit board 1 is placed in the substrate cooling device 6 with a fluid such as nitrogen at about 20 ° C to 50 ° C. Cooled by spouting at a flow rate of 1.2 m 3 / min. 6 shows the temperature of the molten solder of the flow solder bath on the horizontal axis, the In content of the solder used to connect the QFP-LSI to the vertical axis, the conditions where no fracture occurred, and the conditions where the fracture occurred are indicated by the X table. In addition, in FIG. 6, a solid line is a line considered as the boundary of the condition which breaks and a condition which does not occur.

According to the experimental results of the third embodiment, as shown in FIG. 6, it was confirmed that the upper limit of the allowable melting temperature of the flow solder may be increased by about 15 ° C. as compared with the first embodiment shown in FIG. 4. According to the experimental result shown in FIG. 6, when the content of In is 7% by mass, the allowable melting temperature of the flow solder is up to 250 ° C, and when the flow rate of In is 8% by mass, the allowable melting temperature of the flow solder is 245 ° C. When the content of In was 9% by mass, it was confirmed that the allowable melting temperature of the flow solder could be up to 240 ° C.

As a result of the above, if the amount of fluids such as nitrogen is increased to about 1.2 m 3 / min, Sn-Ag- at 240 to 250 ° C. may be added even if the amount of In is added to the reflow solder for surface-mounted parts by about 7 to 9%. It is possible to perform flow soldering using Cu molten solder or the like.

[Example 4]

Similar to the second and third embodiments, the fourth embodiment is a surface mount component (32 mm each QFP-LSI) that is further subjected to reflow soldering while the substrate cooling device 6 is operated when performing flow soldering. 2) the heat dissipation jig 7 having the shape of a square frame made of metal such as aluminum is mounted on the connection portion of the connection part, and the heat dissipation jig 7 is brought into contact with the lead of the surface mounting component 2 so that the upper surface of the circuit board 1 ( 101) is cooled, and the suppression effect of segregation peeling of the surface mount component at the time of flow soldering is improved. At this time, the flow melt solder was Sn-0.7Cu or Sn-3Ag-0.5Cu, and the temperature of the flow solder bath was fixed under water conditions so that the temperature was 250 to 280 ° C.

7 shows the temperature of the molten solder of the flow solder bath on the horizontal axis, the In content of the solder used for the connection of the QFP-LSI on the vertical axis, the conditions where no fracture occurred, and the conditions where the fracture occurred are indicated by the X table. In addition, the solid line in FIG. 7 is a line considered as a boundary between the condition which breaks and a condition which does not occur.

According to the experimental results of the fourth embodiment, as shown in FIG. 7, it was confirmed that the upper limit of the allowable melting temperature of the flow solder may be increased by about 20 ° C as compared with the first embodiment shown in FIG. According to the experimental results shown in FIG. 7, the allowable melting temperature of the flow solder is 250 ° C. when the content of In is 7% by mass, and the allowable melting temperature of the flow solder is 250 when the content of In is 8-9% by mass. It was confirmed that it could be done up to ℃.

As a result of the above, the upper surface of the substrate was cooled to about 1.2 m 3 / min, and the heat dissipation jig was used. Even if 9% of In was added to the reflow solder for surface-mount components, Sn-Ag-Cu at 250 ° C was used. It is possible to perform flow soldering using molten solder or the like. As a result, according to the fourth embodiment, in the case of performing flow soldering using 250 ° C Sn-Ag-Cu molten solder or the like, the amount of In that can be added to the surface mounting component solder is increased to about 9%. It becomes possible, and it becomes easy to fully correspond to low heat resistance electronic components.

[Example 5]

In the fifth embodiment, the lead plating of the surface mount component to be reflow soldered is Pb-free to improve the effect of suppressing segregation peeling of the surface mount component during flow soldering.

However, at this time, the molten solder of the flow solder tank (not shown) is set to Sn-0.8Ag-57Bi, Sn-0.7Cu or Sn-3Ag-0.5Cu (unit: mass%) close to the process composition, and the temperature is The temperature of the flow solder bath was fixed under water so that it became 235 degreeC-280 degreeC.

In each of the samples described above, it was observed whether breakage occurred in the connection portion of the QFP-LSI 2a.

8 and 9 show experimental results in the case of Sn-3 mass% Bi plating and Sn plating, which are the fifth embodiment. 8 and 9 show the molten solder temperature of the flow solder bath on the horizontal axis, the In content of the solder used to connect the QFP-LSI to the vertical axis, and the conditions where no breakage occurred are shown in the following table. Indicated. In addition, the solid line in each figure is a line considered as a boundary of the condition which a break takes place and the condition which does not occur.

In addition, in order to compare with the experimental result of FIG. 4 (using Sn-10Pb plating), the boundary of FIG. 4 is shown with the dotted line in FIG. In addition, in order to compare with the experiment result of FIG. 8 (using Sn-3Bi plating), the boundary of FIG. 8 is shown with the dotted line in FIG.

According to these results, when Sn-3Bi plating is used (FIG. 8), when flow soldering with 250 ° C Sn-Ag-Cu molten solder or the like, the amount of In that can be added to the surface mounting component solder is 8%. It is understood that it is degree. In addition, when Sn plating is used (FIG. 9), when flow soldering with Sn-Ag-Cu molten solder at 250 DEG C or the like, it can be seen that the amount of In added to the surface mounting component solder is about 9%. have. However, when flow soldering with Sn-Ag-Cu fusion solder at 260 ° C or the like, the amount of In that can be added to the solder for surface-mounted parts is about 5%.

As described above, according to the fifth embodiment in which lead plating of the surface mount component is Pb-free, the amount of In that can be added to the reflow solder without cooling the substrate cooling device 6 as in the first embodiment. It can be made into about 8 to 9%, and it becomes easy to fully correspond to a low heat resistance electronic component.

[Example 6]

In the sixth embodiment, in the fourth embodiment, the lead plating of the surface mount component to be reflow soldered is Pb-free, thereby improving the suppression effect of segregation peeling of the surface mount component during flow soldering.

At this time, the molten solder of the flow solder tank (not shown) is set to Sn-0.7Cu (unit: mass%) or Sn-3Ag-0.5Cu (unit: mass%) close to the process composition, and the temperature is The temperature of the flow solder bath was fixed under water so that it was 250-280 degreeC.

In each of the samples described above, it was observed whether breakage occurred in the connection portion of the QFP-LSI 2a.

10 shows the experimental results of the sixth embodiment. 10 shows the temperature of the molten solder of the flow solder bath on the horizontal axis, the In content of the solder used for the connection of the QFP-LSI to the vertical axis, the conditions where no fracture occurred, and the conditions where the fracture occurred were represented by the X table. In addition, in FIG. 10, a solid line is a line considered as a boundary of the conditions which break and a condition which do not occur. In addition, in FIG. 10, the boundary of FIG. 9 is shown with the dotted line for the comparison with the experimental result of FIG. 9 (without using the Sn plating, neither the board top cooling nor the heat dissipation jig).

As shown in Fig. 10, according to the sixth embodiment, even in the case of performing flow soldering with Sn-Ag-Cu molten solder at both temperatures of 250 DEG C and 260 DEG C or the like, it can be added to the surface mounting component solder. The amount of In can be made about 9%, and as a result, it becomes possible to fully respond to low heat resistance electronic components.

The present invention can realize soldering of low heat resistance electronic components such as FPGAs to circuit boards using Pb-free solder alloys.

Claims (17)

Pb-free solder paste composed of an alloy based on Sn- (1 to 4) Ag- (0 to 1) Cu- (7 to 10) In (unit: mass%) on the upper or lower surface of the circuit board. Soldering using a reflow soldering method using a Pb-free solder alloy, characterized in that the soldering. The reflow soldering method using Pb-free solder alloy according to claim 1, wherein the lead of the surface mount component is subjected to Pb-free plating. The reflow soldering method using a Pb-free solder alloy according to claim 2, wherein the Pb-free plating is Sn plating or Sn-Bi plating. Pb-free solder paste made of an alloy based on Sn- (1 to 4) Ag- (0 to 1) Cu- (7 to 10) In (unit:% by mass) on at least an upper surface of the circuit board. A reflow soldering step for soldering using An insertion step of inserting a lead or terminal of an insertion-mounting component into the through hole drilled in the circuit board from an upper surface side; A flux coating step of applying flux to the circuit board after inserting a lead or a terminal of an insert mounting component into the through hole in the insertion step; A preliminary heating step of preliminarily heating the lower surface of the circuit board after applying flux to the circuit board in the flux coating step; In the pre-heating step, a lower surface of the pre-heated circuit board is brought into contact with a jet flow of Pb-free solder, and a flow soldering step of flow soldering the lead or terminal of the inserted component to the circuit board is provided. Mixed mounting method using free solder alloy. The mixed mounting method using a Pb-free solder alloy according to claim 4, wherein, in the reflow soldering step, a lead of the surface mount component is subjected to Pb-free plating. 6. The mixed mounting method using a Pb-free solder alloy according to claim 5, wherein the Pb-free plating is Sn plating or Sn-Bi plating. The process of claim 4, wherein in the flow soldering step, the Pb-free solder is Sn-Cu, Sn-Ag, Sn-Ag-Cu, Sn-Ag-Bi, or a process in which In is added thereto. (Iii) A composition mounting method using a Pb-free solder alloy, which is a composition or a composition close to the process composition. The process of claim 5, wherein in the flow soldering step, the Pb-free solder is Sn-Cu-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Ag-Bi-based, or a process in which In is added thereto. A composition or a method for mounting a mixed material using a Pb-free solder alloy, which is a composition or a composition close to the process composition. The mixed mounting method using a Pb-free solder alloy according to claim 7, wherein in the flow soldering step, a temperature of the jet flow of the Pb-free solder is in a range of 170 ° C to 260 ° C. The mixed mounting method using a Pb-free solder alloy according to claim 8, wherein in the flow soldering step, the temperature of the jet flow of the Pb-free solder is in the range of 170 ° C to 260 ° C. The mixed mounting method using a Pb-free solder alloy according to claim 7, wherein in the flow soldering step, a fluid having a temperature of 50 ° C. or lower is sprayed on the upper surface of the circuit board and cooled. The mixed mounting method using a Pb-free solder alloy according to claim 8, wherein in the flow soldering step, a fluid having a temperature of 50 ° C. or lower is sprayed on the upper surface of the circuit board and cooled. The mixed mounting method using a Pb-free solder alloy according to claim 11, wherein in the flow soldering step, the flow rate of the fluid is 0.3 to 1.2 m 3 / min. The mixed mounting method using a Pb pre-solder alloy according to claim 12, wherein in the flow soldering step, the flow rate of the fluid is 0.3 to 1.2 m 3 / min. The mixed mounting method using a Pb-free solder alloy according to claim 11, wherein in the flow soldering step, a heat dissipation jig is attached to a contact portion of the surface mount component. The mixed mounting method using a Pb-free solder alloy according to claim 12, wherein, in the flow soldering step, a heat dissipation jig is attached to the connection portion of the surface mount component in contact. The mixed mounting structure which mixed-mounted using the mixed mounting method using the Pb-free solder alloy as described in any one of Claims 4, 5, 7 or 8.

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