JP5240268B2 - Laser soldering method - Google Patents

Description

  The present invention relates to a soldering method using a laser, and more particularly, to a laser soldering method that improves soldering performance and reliability.

  Conventionally, electronic component leads are inserted into through-holes (conductors are plated on the inner surface) formed in a printed circuit board, and the conductive lands provided around the through-holes are soldered to the electronic component leads. Thus, electronic components are mounted on a printed circuit board. As a soldering method, flow soldering in which an electrode of an electronic component is immersed in a solder layer and soldering with a soldering iron are known. However, in recent years, due to downsizing of electronic components or increase in mounting density, laser light is used. A laser soldering method in which soldering is performed in a non-contact manner is used (see Patent Document 1). This laser soldering method is attracting attention because it is also suitable when a lead-free solder material is used.

  However, there are some problems in the soldering performance and reliability peculiar to the laser soldering method. For example, the heat reception of the thread solder by the laser beam is not successful, resulting in poor soldering, or the printed circuit board is burnt or the burn of the flux is generated by the laser beam.

JP 2003-204149 A

  In view of the above problems, an object of the present invention is to provide a laser soldering method with improved soldering performance and reliability.

A first aspect of the present invention, as set forth in claim 1, in laser soldering method for soldering by laser irradiation and a land provided around the through hole of the lead and the circuit board of the electronic component, the through Assembling the lead to a shielding plate that shields laser light passing through the hole; inserting the lead into the through hole to project; and irradiating laser light from above in the projecting direction of the lead; and supplying the wire solder from the direction angle is 60 ° to 70 ° or less with the circuit board, wherein the yarn solder break, heat by contact with heated said lead by the laser beam, and This is a laser soldering method in which the thread solder is melted by receiving heat when passing through the laser beam. If it does in this way, solderability can be improved irrespective of the supply direction of a solder material, and mold burn of electronic parts by the laser beam which passes through a through hole can be prevented .

Further, as described in claim 2 , when the bent portion is provided in the lead and the shielding plate is arranged in the bent portion, the laser beam can be completely shielded to prevent mold burn. .

According to a second aspect of the present invention, in the laser soldering method according to claim 3 , wherein the lead of the electronic component and the land provided around the through hole of the circuit board are soldered by laser irradiation, the lead as light reflected from the side surface is incident on the said lands, a step of at least on the basis of the incident angle to the lead side alpha, determining the projection length L or land dimension from the circuit board of the lead, the A step of inserting a lead into the through hole and projecting the lead, a step of irradiating a laser beam from above the projecting direction of the lead, and a direction in which the angle between the solder wire and the circuit board is 60 ° or more and 70 ° or less And the step of supplying, wherein the thread solder receives heat by contact with the lead heated by the laser beam, and the thread solder is a laser beam. A laser soldering method melted by heat as it passes through a medium. In this way, laser soldering that does not cause substrate burning can be performed.

When the lead is not tilted or bent, the protrusion length L or the land size can be determined so as to satisfy the formula of claim 4 .

When the lead has only the inclination of the inclination angle β, the protrusion length L or the land size can be determined so as to satisfy the formula of claim 5 .

When the lead has only a bend of a bending angle α, the protrusion length L or the land dimension can be determined so as to satisfy the formula of claim 6 .

In addition, as described in claim 7 , the wavelength of the laser light is selected from a range of wavelengths from 850 nm to 1100 nm. If it does in this way, generation | occurrence | production of a substrate burn can be suppressed.

The wavelength of the laser beam can be 940 nm as described in claim 8 .

Furthermore, as described in claim 9 , the circuit board can be a circuit board in which a circuit is formed on a glass epoxy substrate by silk screen printing and a solder resist mainly composed of an acrylate resin is applied.

According to a third aspect of the present invention, in the laser soldering method according to claim 10 , wherein the lead of the electronic component and the land provided around the through hole of the circuit board are soldered by laser irradiation, the lead Is inserted into the through hole and protruded, laser light is irradiated from above the protruding direction of the lead, and thread solder is supplied from the direction in which the angle with the circuit board is 60 ° or more and 70 ° or less. step a, wherein the lands a oval land, are soldered by using a laser beam of oval of size that does not protrude from the oval of land, the wire solder, the Heat receiving by contact with the lead heated by laser light, and laser soldering that melts by heat reception when thread solder passes through the laser light Method. In this way, optimal laser irradiation can be performed on the oval land.

(A)-(c) is a figure explaining the laser soldering method of a reference example. It is a figure which shows the laser soldering apparatus for implementing a reference example. (A)-(c) is a figure which shows the relationship between the position of the lead | read | reed in a through hole, and a laser soldering defect rate. (A)-(c) is a figure which shows the relationship between the solder supply angle for demonstrating 1st Embodiment, and a laser soldering defect rate. (A)-(c) is a figure explaining the laser soldering method of 2nd Embodiment. It is a figure which shows the laser soldering method which is another example of 2nd Embodiment. It is a figure which shows the oval-type land around a through hole. It is a figure which shows the laser soldering method of 3rd Embodiment, a comparative example, and these effects. It is a figure which shows an example of the irradiation conditions of the laser used for 3rd Embodiment. (A)-(c) is a figure which shows typically the laser soldering method of 4th Embodiment which considered the conditions in which the reflected light by a lead injects into a land. It is a figure which shows the relationship between the reflective position L of the lead | read | reed by 4th Embodiment, and the arrival distance X of reflected light. It is a figure which shows the effect of 4th Embodiment, Comprising: It is the figure which plotted and showed what the board | substrate burnt generate | occur | produced and what the board | substrate burnt did not generate | occur | produce. It is a figure explaining the structure of the circuit board to which 5th Embodiment is applied. It is a figure which shows the laser absorption factor according to a structure of the circuit board shown in FIG. It is a figure which shows the result soldered using the semiconductor laser of about 940 nm which is an example of 5th Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Reference example)
First, the idea of the reference example will be described with reference to FIGS. As shown in FIGS. 1A and 1B, the conductive lands 14 provided by, for example, copper plating around the through holes 15 provided through the printed circuit board and the leads 12 are soldered. When attaching, the lead 12 of an electronic component is inserted into the through hole 15 from below, and the solder wire 13 is melted and soldered by the laser beam 11 from the laser source provided at the top of the printed circuit board. Here, the solder 13 is guided by the solder guide 28 and fed out to the laser light irradiation region at a supply angle θ = 45 ° by a robot (not shown).

  In general, the lead 12 does not necessarily pass through the central portion of the through hole 15, but often passes through the peripheral portion of the through hole 15, as shown in FIGS. In FIG. 1A, the lead 12 inserted into the through hole 15 is on the left side of the drawing, that is, at a location near the solder guide 28. On the other hand, in FIG. 1B, the lead 12 inserted into the through hole 15 is on the right side of the drawing, that is, at a position far from the solder guide 28. FIG. 1C is a top view of FIG. 1A and shows the positional relationship between the lead 12 and the through hole 15.

  In laser soldering, heat is applied to the thread solder 13 by laser light as described above. There are two modes for receiving heat of the thread solder, one is heat reception by contact between the heated lead 12 and the thread solder 13, and the other is heat reception when the thread solder 13 passes through the laser beam 11. .

  First, considering the case where heat is received by contact between the lead 12 and the thread solder 13, the energy density of the laser beam 11 is highest at the center of the laser irradiation diameter, and as shown in FIGS. Is not at the center of the through-hole 15 and is offset toward the periphery, the lead 12 cannot receive the laser beam 11 efficiently. Therefore, even if the lead 12 and the thread solder 13 come into contact with each other, the thread solder 13 cannot receive heat sufficiently, causing a soldering failure.

  As a countermeasure, there is a method of increasing the laser output in anticipation that the position of the lead 12 is offset in advance. In this case, when the inner diameter dimension of the through hole 15 is 1, when the position of the lead 12 is outside 0.7, it is known that about 30% of the laser output increase is required. However, it was found that if the laser output was increased, the peeling rate of the copper plating between the through hole 15 and the land deteriorated from 30% to 60%, and the target of 50% or less could not be achieved.

  Next, considering the case where heat is received when the thread solder 13 passes through the laser beam 11, the lead 12 is offset to the peripheral edge of the through hole 15 in both FIGS. 1 (a) and 1 (b). ) Has a longer time from when the solder wire 13 starts to enter the laser beam 11 until it contacts the lead 12 than when the solder wire 13 receives heat directly from the laser beam 11. Further, since it passes through the central portion, it can receive laser light with high energy density.

  The reference example is obtained from such consideration, and recognizes the position of the lead 12 in the through hole 15 and controls the solder supply direction. For example, when the positional relationship between the solder 13 and the lead 12 is as shown in FIG. 1A, the solder 13 is placed in FIG. 1A so that the positional relationship as shown in FIG. That is, a relatively long distance from the direction in which the solder 13 starts to enter the laser beam 11 until it contacts the lead 12 is supplied from the moving direction. That is, when the positional relationship as shown in FIG. 1A is recognized, the robot arm supporting the solder guide 28 is moved to realize the positional relationship as shown in FIG. In this way, the solderability can be improved without increasing the laser output, and the printed circuit board land is not adversely affected.

  FIG. 2 shows a laser soldering apparatus for carrying out the reference example. The lead 1 of the electronic component 16 is inserted into the through hole 15 of the printed board 31 and soldered. The laser beam 11 from the laser source 21 is irradiated toward the lead 12. The thread solder 13 for soldering the lead 12 to the printed circuit board 31 is supplied through a solder guide 28. In this embodiment, a CCD camera 23 that is an imaging device is provided, and an image of the lead 12 that passes through the through hole 15 is acquired. That is, the light beam reflected from the lead 12 or the printed circuit board 31 is reflected by the half mirror 26 and enters the CCD camera 23. An image obtained by the CCD camera shows the relationship between the lead 12 and the through hole 15 as shown in FIG. Based on this image information, the control device 25 controls the solder supply device 27 so as to supply the thread solder from the direction in which the distance between the lead 12 and the land 14 around the through hole 15 is the largest. That is, the solder guide 28 goes around the lead 12 and supplies thread solder from an optimum position. The positions of the laser source 21 and the CCD camera 23 may be interchanged so that the laser light is reflected by the half mirror 26.

  When the position of the lead is away from the center of the through hole 15, as described above, there is a significant difference with respect to heat reception depending on the solder supply direction. Although the method of moving the solder guide 28 so that it is located farthest from the lead 12 and controlling the solder supply direction has been shown, it can also be controlled as follows.

  As shown in FIG.1 (c), the through hole 15 is divided into 4 and the 1st-4th areas 1-4 which are each a quadrant are set. In the figure, the lead 12 is in the third area 3. Here, if the thread solder 13 is supplied from the area other than the area 3 where the lead 12 exists toward the lead 12, the peeling rate can be reduced. Therefore, instead of supplying the thread solder from the position where the lead 12 and the land 14 are at the maximum distance, the thread solder is passed from any of the areas 1, 2, 4 which are not the area 3 where the lead 12 exists. You may make it supply.

  Furthermore, in order to find out specific conditions, various conditions were set and laser soldering was actually performed. The results shown in FIGS. 3A to 3C are based on the relationship between the deviation r, which is the distance between the center of the through hole 15 and the center of the lead 12, and the solder supply direction d. Was investigated. In FIG. 3, the solder supply direction d is fixed to the third area (the area number is shown for reference in the figure), the leads are arranged in the first to fourth areas, and the laser soldering is performed. I did. The radius of the through hole 15 is R, and the solder supply angle θ to the printed wiring board is 45 °.

  In FIG. 3A, the shift amount r is in a relationship of r ≧ (1/2) R with respect to the radius R of the through hole, and the lead 12 is farthest from the center of the through hole 15. When the lead 12 is in the third area and the solder is supplied through the third area, the soldering failure occurs in the ratio of 25 out of 30 leads. When there are leads 12 in other areas, no defects have occurred.

  In FIG. 3B, the shift amount r is (1/4) R ≦ r <(1/2) R, and is closer to the center of the through hole 15 than (a). In this case, the defect rate is lower than (a), but if the lead 12 is still in the third area and solder is supplied through the third area, soldering is performed at a rate of 15 out of 30 pieces. A defect has occurred. When there are leads 12 in other areas, no defects have occurred.

  In FIG. 3C, the shift amount r is (1/8) R ≦ r <(1/4) R, which is closer to the center of the through hole 15 than in FIG. 3B. In this case, even if the lead 12 was in the third area and the solder was supplied through the third area, no defect occurred. Furthermore, it can be seen that when the amount of deviation r approaches the center of the through hole, no defect will naturally occur from any direction.

  Therefore, when the shift amount r, that is, the distance between the through-hole center and the lead center is ¼ or more of the through-hole radius R, it is necessary to supply solder from the area other than the quadrant area where the lead exists. I understand that. Accordingly, supplying solder from an area other than the quadrant area where the lead exists is sufficient as a laser soldering method that does not cause solder defects regardless of the magnitude of the deviation r.

(First embodiment)
4A to 4C show the solder supply angle θ (see FIG. 1A) when the deviation amount r between the through hole 15 and the lead 12 is r ≧ (1/2) R. The result of changing and soldering is shown.

  FIG. 4A shows a case where the solder supply angle θ is 50 °, and when the lead 12 is in the third area and the solder is supplied through the third area, 14 out of 30 are provided. A soldering defect has occurred. However, compared with FIG. 3A, the defect rate is improved by increasing the supply angle from 45 ° to 50 °. When there are leads 12 in other areas, no defects have occurred. This is the same as FIG.

  FIG. 4 (b) shows the occurrence of defects even when the solder supply angle θ is 60 ° and the lead 12 is in the third area and the solder is supplied through the third area. Absent. When there are leads 12 in other areas, no defects have occurred.

  In FIG. 4C, the solder is supplied at an angle of 70 ° when the solder supply angle θ is further increased. Also in this case, even when the lead 12 is in the third area and the solder is supplied through the third area, no defect is observed. When there are leads 12 in other areas, no defects are generated as in (a) and (b).

  According to these results, no matter where the lead 12 passes through the through-hole 15, the solder supply angle is set to 60 ° or more so that no laser soldering defect occurs regardless of the solder supply direction. Is shown. This is due to the fact that by increasing the solder supply angle, the distance from when the solder enters the laser irradiation area until it reaches the lead becomes longer, and sufficient time for heat reception can be secured. It is. Therefore, instead of the above-described laser soldering method in which solder is supplied from an area other than the quadrant area where the lead exists, the solder may be supplied at a solder supply angle of 60 ° or more.

  When the solder is supplied from an area where no lead exists in the four divided areas as described above, the degree of freedom of the solder supply position is increased, and the soldering time can be shortened. When the solder supply angle is 60 ° or more, the solder supply position can be fixed, and the soldering time can be further shortened.

  This embodiment is effective when a normal lead-containing solder is used as the solder material to be used, but is particularly effective when a lead-free solder material that requires a larger amount of heat input is used. The following is an example common to all embodiments, but a semiconductor laser is used as the laser source, eutectic solder of 63% Sn is used as the lead-containing solder material, and Sn-- 3Ag-0.5Cu is used. Further, it has been confirmed that the same effect can be obtained even if a YAG laser is used instead of the semiconductor laser, except for the fifth embodiment which limits the wavelength of the laser.

In this embodiment, the lead 12 is inserted from below the printed circuit board, and laser light is irradiated from above the printed circuit board. Instead, the lead 12 is inserted from below the printed circuit board and the laser light is emitted. You may make it irradiate from the downward direction of a printed circuit board.
(Second Embodiment)
In general laser soldering, as shown in FIG. 5A, for example, a lead 12 protruding from a component 16 molded in an epoxy-based material is inserted into a through hole 15 of a printed circuit board 31, and then, As shown in FIG. 5B, while supplying thread solder (not shown), laser light 11 is irradiated from above the printed circuit board to heat the lead 12 or thread solder.

  In order to securely insert the lead 12 into the through hole 15, a clearance having a size in the through hole 15 is required. However, as can be seen from FIG. 5B, when the laser beam 11 is irradiated and the lead 12 is heated, the laser beam 11 passes through the clearance of the through hole 15 and reaches the mold part. In many cases, this caused mold burn 17-1 in the mold part of the component 16.

  In the second embodiment of the present invention, as a countermeasure, as shown in FIG. 5C, a shielding plate 18 is assembled to the lead 12 so as to shield the laser beam 11 passing through the through hole 15 of the substrate 31. To do. By providing such a shielding plate, the laser light from the through hole 15 can be shielded to some extent. However, since the through-hole 181 for assembling the shielding plate 18 to the lead 12 also requires a clearance, the passing light is also generated, and the mold burn 17-2 occurs to a lesser extent.

  In order to completely block the laser beam, as shown in FIG. 6, the lead 12 is bent so that the lead 12 has a curved portion 19, and the through hole 181 of the shielding plate 18 is passed through the curved portion 19. In this way, the lead 12 is assembled to the printed circuit board 31. As is apparent from FIG. 6, when the shielding plate 18 having the curved portion 19 is used, the optical path of the laser light 11 can be removed even if the through hole 181 of the shielding plate 18 has a clearance.

  In FIG. 6, the distance between the component 16 and the printed board 31 is 13 mm, the curved portion 19 is 5.5 mm from the component 16, that is, 7.5 mm from the printed board, and the shielding plate is assembled. For example, there is an inverter in which five lead pins in a row are arranged in two rows as a specific insertion part. In this case, a curved portion is provided in all of the ten pins, and one piece having a corresponding through hole is provided. The shield plate is assembled.

When such a shielding plate 18 is used, the laser beam 11 is shielded by the shielding plate 15 and cannot reach the mold portion 16. Therefore, it is possible to completely prevent mold burning of the parts.
(Third embodiment)
In both the first and second embodiments, the laser beam is also directly applied to the land 14. Currently, the land area tends to decrease as the pitch of the terminals of the components mounted on the printed wiring board is reduced. When the land area is reduced, the solder fillet is reduced accordingly and the reliability is also lowered. Therefore, in the through-hole component, instead of a circular land, an oval land is generally adopted as shown in FIG. That is, the land width is decreased in the narrow pitch direction, and the land width is increased in the other directions.

  The third embodiment employs an optimum laser irradiation method for the oval land to prevent laser soldering performance improvement and substrate burnout.

  Next, a third embodiment will be described with reference to FIG. The upper half of FIG. 8 shows irradiation modes S1 to S4 in which laser irradiation is performed on an oval land, with reference to an irradiation mode C in which a circular laser is irradiated to a circular land. Among these, 3rd Embodiment is irradiation aspect S3. The lower half of FIG. 8 shows a graph of soldering failure rate and burn occurrence rate after laser soldering corresponding to each irradiation mode (C, S1 to S4). In the graph corresponding to each irradiation mode, the left bar graph shows the soldering failure rate, and the right hatched bar graph shows the burn occurrence rate.

  In each irradiation mode in the upper half of FIG. 8, the solid line indicates the shape of the outer periphery of the land, and the broken line indicates the laser beam shape. In the irradiation mode C, the diameter of the circular land is φa = 2.00 mm, and the diameter of the laser beam is φa1 = 1.8 mm. The short diameter a = 2.0 mm and the long diameter b = 2.5 mm of the oval land in the irradiation modes S1 to S4, the short diameter a1 = 1.8 mm, and the long diameter b1 = 2.3 mm of the laser beam. In the aspect S4, the inclination angle α = 45 °.

  Furthermore, the graph corresponding to each aspect shows the rate of occurrence of poor soldering and burning when soldering is performed with a semiconductor laser having a wavelength of about 810 nm under the irradiation conditions of FIG. According to the irradiation conditions of FIG. 9, first, the laser beam is irradiated for 0.5 to 1.5 seconds at an output of 30 W to heat the leads and lands in advance. Here, the range of the heating time is 0.5 to 1.5 seconds. If the heating time is too long, the copper plating of the through holes or lands may be peeled off. This is because the heating time cannot be adjusted, and the heating time can be adjusted. When the heating is completed, the soldering is performed by irradiating a laser beam with an output of 19 W for 1.9 seconds while supplying the solder.

As shown in irradiation mode C, a laser beam having a diameter of φa1 (a> a1) slightly smaller than the land diameter a is applied to a circular land having a land diameter φa so that the laser beam does not directly hit the substrate. Yes. In this case, both soldering defects and substrate burnout hardly occur. Here, the diameter of the laser beam refers to a diameter obtained from “a beam radius of 1 / e ² (13.5%) level in a Gaussian profile”.

  Through the irradiation modes S1 to S4, the oval lands have the same shape, the short diameter is a, and the long diameter is b (b> a). The irradiation mode S1 shows a case where a circular laser beam having the same irradiation diameter a1 as that in Reference Example C is applied to an oval land. As is apparent from the figure, in the circular laser beam having the irradiation diameter a1, there are many portions where the laser beam is not irradiated, solder deficiency occurs due to insufficient heating, and the incidence of defective soldering is high (FIG. 8). (Refer to the graph corresponding to the irradiation mode S1).

  The irradiation mode S2 is a case where the diameter of the laser beam is increased and the laser beam having a diameter of b1 (b> b1) slightly smaller than the major axis b is irradiated in order to sufficiently apply the laser beam to the oval land. Since b1 is larger than the minor axis a1, the laser beam protrudes from the land at both ends of the minor axis. In such a portion, there is a problem that the laser beam directly hits a resin portion or a solder resist which is a base material of the printed circuit board and the portion is burnt. As shown in the graph of the irradiation mode S2, the occurrence rate of soldering failure is small, but the burn occurrence rate is high.

  The irradiation mode S3 is the present embodiment, and an oval type laser beam having a minor axis a1 slightly smaller than the minor axis a of the land and a major axis b1 slightly smaller than the major axis b of the land is used. As is apparent from the graph corresponding to the irradiation mode S3 shown in the figure, almost no soldering defects or burns occur. In the present embodiment, the shape of the oval type laser beam is obtained by using two laser sources each having a laser beam diameter a and irradiating the laser beam so as to partially overlap each other. The laser beam is generated. Alternatively, an oval laser beam may be obtained using an appropriate lens.

Irradiation mode S4 is a case where the long axis of the land and the long axis of the laser beam are inclined by an angle α in spite of the use of the oval type laser beam. In such a case, the laser beam is not a land. Irradiation will cause burning. As can be seen in the graph corresponding to the irradiation mode S4, it can be seen that the burn is occurring at a high rate. In order to prevent the long axis of the land and the long axis of the laser light from being inclined, the angle of the laser light is adjusted so that the long axis of the land and the long axis of the laser light coincide with each other. Furthermore, it is one of the measures to reduce the shape of the laser beam so that it does not protrude even if it is tilted to some extent.
In order to determine an oval laser beam slightly smaller than this for the oval land, the beam shape is confirmed by, for example, a beam profiler before actual soldering starts. At this time, it goes without saying that not only the shape but also the inclination is adjusted.

  Of course, the specific defect occurrence rate in the graph of FIG. 8 varies depending on each parameter and laser irradiation conditions.

According to the third embodiment, the oval land is irradiated with the oval laser beam, so that the laser beam is efficiently applied to almost the entire surface of the land, and laser soldering without defective soldering and burning can be performed. . Since the oval laser beam can be easily formed by using two circular laser beams, the oval laser beam can be formed with a simple configuration.
(Fourth embodiment)
As described in the third embodiment, when the laser beam deviates from the land of the printed circuit board and irradiates the printed circuit board itself, the substrate is burned. However, even if the laser beam does not directly hit a portion outside the land of the printed circuit board, burning may occur. This is a case where the laser beam is reflected from the side surface of the lead to irradiate the substrate outside the land. When laser light is irradiated from directly above, ie parallel to the lead, the laser light will not be reflected on the lead, but in reality this is rare and the position and inclination of the lead Alternatively, the laser beam is reflected from the side surface of the lead by bending, and in some cases, the substrate outside the land is irradiated. Whether or not the reflected light of the laser light irradiates outside the land is determined by conditions such as the length, inclination, land size, and laser irradiation angle of the terminal.

  10A to 10C show a state in which a laser beam is reflected from the side surface of the lead when a lead wire is inserted into the through hole of a printed wiring board such as glass epoxy from below and irradiated with laser light from above. Is schematically shown. It can be easily imagined that burns due to reflection are most likely to occur when the lead is in contact with the wall surface of the through-hole and the side surface in contact with the laser beam is reflected and reflected. Is assumed. In (a), the lead is not tilted or bent, and the lead is in contact with the wall surface of the through hole. In (b), the lead itself is not bent but inclined, and the lead is in contact with the lower end of the through hole. In (c), the lead itself is bent, the lead is in contact with the upper end of the through hole, and is bent from the upper end to the inside of the through hole.

  Here, when X is the arrival distance of the reflected light and Y is the land dimension, if the arrival distance X of the reflected light is smaller than the land dimension Y, that is, if X <Y, the substrate is not burned. it can.

In the case where there is no inclination or bending of the lead in (a), the arrival distance X of the reflected light when the laser beam with the incident angle α is reflected by the side surface of the lead separated by L from the printed board is:
X = L · tanα (1)
Given in.

When the lead in (b) is inclined by an angle β, the laser light is incident on the side surface of the lead at an angle (α + β) and reflected at the same angle. The reach distance X of the reflected light at that time is approximately,
X = (L · tan (α + β) −T · tanβ) / cosβ (2)
Given in. T is the thickness of the substrate.

Similarly, the reach of the reflected light in the case where the lead is bent by an angle γ (c) is approximately,
X = (L · tan (α + γ) −L · tanγ) / cosγ (3)
It is given by (3).

  In any case, if the reach distance X of the reflected light is smaller than the land dimension Y, the substrate does not burn. That is, α, β, γ, Y, T, and L may be satisfied so that X <Y.

  FIG. 11 shows the reflection position L and the reflection in the range of the inclination angle β = 0 to 10 ° and the bending angle γ = 0 to 10 °, with the reflection angle α = 10 ° and the substrate thickness T = 1.6 mm in FIG. It is the result of calculating the reach distance X of light. Specifically, when there is no inclination or bending (β = γ = 0 °), no bending (bending angle γ = 0 °), and inclination angles β = 2 °, 4 °, 6 °, 8 °, 10 ° In this case, the reflection position L and the reflected light reach distance X are plotted when the bending angle γ = 2 °, 4 °, 6 °, 8 °, and 10 ° without inclination (β = 0 °). From this figure, it is possible to calculate the protrusion length L of the lead in which the substrate is not burned when the land dimension Y is given (reflected light does not reach the outside of the land). That is, the value of L when Y = X is obtained, and if the lead length is actually smaller than L, the reflected light does not reach the outside of the land, and the substrate is not burned.

  For example, assuming that the land dimension Y is 0.25 mm, L at which X = 0.25 mm is about 1.67 mm. That is, under the conditions of α = 10 °, T = 1.6 mm, β = 0-10 °, γ = 0-10, X = Y = 0.25 mm, L≈1.67. According to this, if the protrusion of the lead from the substrate is 1.7 mm or less, the inclination is 10 degrees or less, the substrate thickness is 1.6 mm, and the land dimension is 0.25 mm or more, the substrate will not burn. be able to.

  FIG. 12 shows a semiconductor laser having a wavelength of about 810 nm, and the tilt angle β and the position where the lead reflects the laser beam, that is, the protruding length L, are changed with respect to the tilted lead as shown in FIG. Actually, soldering was performed, and the occurrence of substrate burning was observed. Taking the protrusion amount L on the horizontal axis and the inclination angle β of the lead on the vertical axis, x indicates that the substrate burns at 4 pins or more per 100 pins, and 1 to 3 indicates that the substrate burns. And plotting the case where the substrate was not burnt as ◯. As shown in the figure, when the inclination angle β is 10 ° or less and the protruding length L of the lead is 1.6 mm or less, the substrate is not burned.

Further, the lead having a rectangular cross-sectional shape is used. However, using a lead having a circular or elliptical cross-sectional shape is more effective because the laser light reflected on the side surface of the lead is reduced.
(Fifth embodiment)
In the fourth embodiment, the condition that the laser beam does not enter the substrate is obtained in order to prevent the substrate from being burned. However, the substrate burn occurs in the first place because the substrate absorbs the laser beam. Therefore, it was investigated under what conditions the substrate easily absorbs laser light. The ease of absorption is
Absorbance≈100− (transmittance + reflectance) (4)
It evaluated by the absorption rate represented by these. The transmittance and reflectance in Equation (4) were measured with a spectrophotometer. According to the spectrophotometer, it is possible to irradiate the sample with light of various wavelengths separated by the prism, and to measure the absorptance and reflectance at each wavelength at that time.

  FIG. 13 shows an outline of the configuration of the measured sample.

  (K1) A 1.6 mm thick glass epoxy substrate which is the base material of the printed wiring board itself.

  (K2) A solder resist having a thickness of 70 μm formed of a resist resin whose main component is an acrylate resin on (k1), that is, a glass epoxy substrate + resist (70 μm).

  (K3) A silkscreen ink mainly composed of an epoxy resin containing titanium oxide and subjected to silkscreen printing of 10 μm on (k1), that is, a glass epoxy substrate + silk (10 μm).

  (K4) (k2) subjected to silk screen printing of (k3), that is, glass epoxy substrate + resist (70 μm) + silk (10 μm).

  (K5) A copper land having a thickness of 0.06 mm formed on (k1), that is, a glass epoxy substrate + Cu land (0.06 mmt).

  (K6) Ni-P plating (about 6 μm) applied to a 0.5 mm thick copper lead, followed by lead-free solder plating (about 10 μm).

  FIG. 14 shows the absorptance of the configurations (k1) to (k6) shown in FIG. The horizontal axis represents wavelength (nm) and the vertical axis represents absorption rate (%). From FIG. 14, it can be seen that the wavelengths of the laser that are difficult to be absorbed by the printed wiring board exist around 1950 nm and around 500 nm. For reference, the wavelengths of YAG laser (double modulation), He-Ne laser, semiconductor laser, and YAG laser are described. As can be seen, laser light that can be substantially used is around 1950 nm and 500 nm. not exist. For example, there is no laser light having a wavelength near 1950 nm. Moreover, although it exists in the vicinity of 500 nm, generating a practical output laser beam is not practical because it requires enormous costs. Practically usable wavelengths are a semiconductor laser present at about 800 nm to about 960 nm and a YAG laser present at about 1064 nm.

  In the graph of the third embodiment (FIG. 8) and the graph of the fourth embodiment (FIG. 12), the printed wiring board having the configuration of (k4) in FIG. 13 is soldered by a semiconductor laser having a wavelength of about 810 nm. Is. As described in the fourth embodiment, the state of occurrence of substrate burn is as shown in FIG. Therefore, the configuration of (k4) in FIG. 13 (screen printing is performed on a glass epoxy substrate with a silk screen ink mainly composed of an epoxy resin containing titanium oxide, and a solder resist is formed by a resist resin mainly composed of an acrylate resin. In the graph of FIG. 14, it is understood that the wavelength at which the absorption peak of (k4) does not appear should be selected for the printed circuit board of FIG. For example, a wavelength range of 850 nm to 1100 nm can be selected and used. FIG. 15 shows the result of soldering using a semiconductor laser with a wavelength of 940 nm under the same conditions as those obtained with the result of FIG. 12 using a semiconductor laser with a wavelength of 810 nm. According to FIG. 15, it can be seen that the substrate is not burned in any case.

As described above, the substrate was not burned only by changing the wavelength of the laser from about 810 nm to about 940 nm. As described above, the substrate burn is greatly influenced by the configuration of the printed wiring board and the wavelength of the laser beam, in addition to the terminal (lead) length, inclination, bending, land size, and laser irradiation angle. . In this embodiment, since the wavelength of the laser beam that hardly causes the substrate burn is selected according to the configuration of the printed wiring board, even if the laser beam is irradiated to a portion off the land of the printed wiring board, the substrate burns. Occurrence is suppressed.
(Sixth embodiment)
After normal laser soldering, black burns may remain on the solder. This black burn was found to be due to the flux used with the solder material. In this embodiment, a flex material is selected to prevent the above-mentioned burn.

  Generally, a solder used for laser soldering includes a flux together with a solder material, and a rosin generally called pine ani is used as the flux. When rosin is examined for temperature and mass changes by thermogravimetry (TG) method, general rosin turns brown at the temperature at which soldering is performed, and when the temperature is further increased, components that cannot evaporate. It was found that carbonized and blackened tar remained. Therefore, when laser soldering is performed using such a material in a situation where no countermeasures are taken, scorching will occur as described above.

  On the other hand, in the case of rosin that has been purified by distillation or a flux of synthetic resin, it was found that when measured by the TG method, there is little discoloration of the residue and it is difficult to carbonize. Therefore, in this embodiment, laser soldering is performed using such a material. As a result, the burn of the residual flux itself can be reduced.

  In addition, such a refined distilled product had a thermal weight percent (TG), which is a weight reduction rate measured by a TG method of a flux material at about 400 ° C., of 15% or less.

  As mentioned above, although embodiment of this invention was described, each embodiment can also be used independently, but can also be used in combination. In order to improve the soldering performance and reliability, it is more effective when used in combination.

DESCRIPTION OF SYMBOLS 11 Laser beam 12 Lead 13 Solder 14 Land 15 Through hole 16 Electronic component 18 Shielding plate 21 Laser source 23 CCD camera 25 Control part 26 Half mirror 27 Solder supply part 28 Solder guide 31 Circuit board

Claims (10)

In the laser soldering method of soldering the lead of the electronic component and the land provided around the through hole of the circuit board by laser irradiation,
Assembling the lead to a shielding plate that shields laser light passing through the through hole;
Inserting the lead into the through hole to protrude;
Irradiating laser light from above in the protruding direction of the leads;
Supplying thread solder from a direction in which the angle with the circuit board is 60 ° or more and 70 ° or less;
With
The laser soldering method, wherein the thread solder is melted by heat reception by contact with the lead heated by the laser light and heat reception when the thread solder passes through the laser light. Providing the lead with a bent portion;
In the step of assembling the lead to the shield plate, laser soldering method according to claim 1 for arranging the shielding plate bent portion of the lead. In the laser soldering method of soldering the lead of the electronic component and the land provided around the through hole of the circuit board by laser irradiation,
As light reflected from the lead side is incident in the land, the method comprising at least on the basis of the incidence angle α of the lead side, determines a protruding length L or land dimension from the circuit board of the lead ,
Inserting the lead into the through hole to protrude;
Irradiating laser light from above in the protruding direction of the leads;
Supplying thread solder from a direction in which the angle with the circuit board is 60 ° or more and 70 ° or less;
With
The wire solder is over The soldering method heat due to contact with the lead heated by the laser beam, and the solder wire is melted by the heat as it passes through the laser beam. When the lead is not tilted or bent, the step of determining the projecting length L or land size of the lead from the circuit board includes:
Land size> L ・ tanα
The laser soldering method according to claim 3 , wherein the protrusion length L or the land size is determined so as to satisfy the above. When the lead has only an inclination of an inclination angle β, the step of determining the projecting length L or the land size of the lead from the circuit board, T is the thickness of the circuit board,
Land dimension> (L · tan (α + β) −T · tanβ) / cosβ
The laser soldering method according to claim 3 , wherein the protrusion length L or the land size is determined so as to satisfy the above. When the lead has only a bend of a bending angle α, the step of determining the projecting length L or land size of the lead from the circuit board is as follows: T is the thickness of the circuit board,
Land Dimension> (L · tan (α + γ) −L · tan γ) / cos γ
The laser soldering method according to claim 3 , wherein the protrusion length L or the land size is determined so as to satisfy the above. Wavelength of the laser light, the laser soldering method according to claim 1 or 3 is selected from the following wavelength 1100nm at least 850 nm. The laser soldering method according to claim 7 , wherein a wavelength of the laser light is 940 nm. The laser soldering method according to claim 7 or 8 , wherein the circuit board is a circuit board formed by forming a circuit on a glass epoxy board by silk screen printing and performing a solder resist mainly composed of an acrylate resin. In the laser soldering method of soldering the lead of the electronic component and the land provided around the through hole of the circuit board by laser irradiation,
Inserting the lead into the through hole to protrude;
Irradiating laser light from above in the protruding direction of the leads;
Supplying thread solder from a direction in which the angle with the circuit board is 60 ° or more and 70 ° or less;
With
The land is an oval land,
Soldered using an oval type laser beam of a size that does not protrude from the oval type land formed by irradiating two circular laser beams in an overlapping manner ,
The laser soldering method, wherein the thread solder is melted by heat reception by contact with the lead heated by the laser light and heat reception when the thread solder passes through the laser light .

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