JP4833926B2 - Soldering method - Google Patents

Description

  The present invention relates to a soldering method for mounting an insertion type electronic component on a circuit board on which a printed wiring board or a surface mounting component is mounted using a lead-free solder material.

  In recent years, there has been a strong demand for improvement in the reliability characteristics of electronic circuit boards built in as electronic devices have higher performance and diversified environments. For this reason, in electronic component mounting, there is an increasing demand for improvement in reliability characteristics such as mechanical strength and thermal shock strength of a joint formed by soldering the electronic component to a substrate.

  In addition, solder materials used for soldering electronic components to printed circuit boards are subject to laws and regulations concerning the removal of lead from waste products and the prohibition of use of lead from the viewpoint of global environmental protection. Switching to lead-free solder materials that do not contain it is progressing.

  The problems of soldering such as lift-off and shrinkage in the flow soldering of insertion-type electronic components to the board using lead-free solder materials are due to segregation of the solder additive elements of the solder material and the original solder composition. Is known to be caused by the formation of fragile alloys with different low melting points, and by rapidly solidifying the solder, the segregation phenomenon is alleviated and the growth time of the fragile alloy phase is shortened. It is said that it is effective in reducing the above-mentioned problems.

  The following manufacturing methods and soldering methods have been proposed for the purpose of improving the connection reliability between the electronic component and the substrate by suppressing the occurrence of lift-off, shrinkage and the like, which are defects in soldering.

  Japanese Patent Application Laid-Open No. 11-354919 discloses a cooling zone partitioned by a heat shield immediately after flow soldering in a flow soldering method for mounting an electronic component on a substrate using a lead-free solder material containing Bi. And the temperature range from the liquidus temperature vicinity to the solidus temperature vicinity is cooled at about 10 to 20 ° C./second, and the second cooling rate: the temperature range near the solidus temperature is about 0. A method of manufacturing an electronic circuit board that has been gradually cooled at 1 to 5 ° C./second to suppress lift-off and improve connection reliability is described (Patent Document 1).

  In Japanese Patent Laid-Open No. 2001-15903, in flow soldering for mounting electronic components on a substrate using a lead-free solder material, a cooling unit is provided in the flow soldering equipment line, and after the flow soldering process, rapid cooling is performed. In the process, the circuit board is cooled with a refrigerant liquid having a temperature lower than 1/2 of the soldering temperature or a temperature selected in advance of 20 ° C. to 120 ° C., and cracks (lift-off phenomenon) occur in the solder joints. A strong soldering method and apparatus that have been prevented are described (Patent Document 2).

  Japanese Patent Laid-Open No. 2002-141658 discloses a flow soldering for mounting an electronic component on a substrate using a lead-free solder material, and includes a cooling chamber device in the flow equipment line, between the flow tank and the cooling chamber. In order to prevent the solder from starting to solidify, an adjustment zone having an ambient temperature that can ensure a molten state of the solder is provided, and the molten solder material is adhered to a predetermined portion of the substrate in the solder material supply zone Thereafter, the solder material adhering to the substrate in the adjustment zone is soaked in a molten state, and rapidly, for example, about 200 ° C./min to 500 ° C./min, more preferably about 300 ° C./min to 500 ° C./min in the cooling zone. Describes a soldering method and apparatus that reduce the occurrence of lift-off by cooling with (Patent Document 3).

Japanese Patent Laid-Open No. 11-354919 JP 2001-15903 A JP 2002-141658 A

  However, in Patent Document 1, a heat shield is provided between the flow zone and the cooling zone, but due to the temperature gradient generated between the flow zone and the cooling zone, the cooling rate at the front and rear ends of the substrate is reduced. A difference occurs and the entire substrate cannot be cooled at a uniform cooling rate. In addition, there is no description about the size of the substrate, and in the case of a large substrate, the difference in cooling rate between the front and rear ends of the substrate becomes more significant, and solidification may have started before reaching the cooling zone. There is a problem that the entire substrate cannot be cooled at a uniform cooling rate.

  Patent Document 2 does not have the heat shield plate of Patent Document 1, but similarly has a problem that the entire substrate cannot be cooled at a uniform cooling rate due to a temperature gradient generated between the flow zone and the cooling zone. .

  Further, according to Patent Document 3, an adjustment zone is provided, so that countermeasures against solidification of solder before cooling are taken. Due to the temperature gradient generated in FIG. 1, there is a difference in the cooling rate between the front and rear ends of the substrate, and there is a problem that the entire substrate cannot be cooled at a uniform cooling rate.

  Summarizing the problems of Patent Documents 1 to 3 above, when the substrate is transported to the cooling zone by a conventional belt conveyor, the substrate is moved at the front, center, and rear ends of the substrate at the position where the substrate enters the cooling zone. There is a problem that a difference occurs in the surface temperature, a difference occurs in the cooling rate at the front end, the central part, and the rear end of the substrate in the transport direction, and the entire substrate cannot be cooled at a uniform cooling rate. Thus, when the whole board | substrate cannot be cooled with a uniform cooling rate, the cooling conditions of each solder joint part on a board | substrate differ, and there exists a problem that the quality of the soldering of an electronic component varies.

  The present invention relates to the occurrence of lift-off and shrinkage in a soldering method for mounting an insertion-type electronic component on a lead-free printed circuit board on which a printed wiring board or surface-mounted component is mounted using a lead-free solder material. It is an object of the present invention to provide a method for soldering a printed wiring board or a printed circuit board, which reduces the generation of nests and has excellent connection reliability between an electronic component and a board.

The printed wiring board or printed circuit board soldering method according to the first aspect of the present invention is a method of soldering a printed circuit board on which a printed wiring board or surface-mounted component is mounted using a lead-free solder material. An electronic component is inserted into a through hole of the printed wiring board or the printed circuit board, and a printed circuit mounting board on which the insertion type electronic component is mounted is manufactured by flow soldering, and then the printed circuit mounting board is placed in a heating furnace. The printed circuit mounting board mounted on the printed circuit board using hot air blown to a range including the entire surface of the printed circuit mounting board from a heating nozzle disposed in the vertical direction of the printed circuit mounting board inside the heating furnace. After heating the entire surface of the printed circuit board from the cooling nozzles arranged in the vertical direction of the printed circuit board inside the heating furnace By cooling the printed circuit mounting board by utilizing the refrigerant ejected to the range including and the solder of the solder joint portion of the insertion type electronic component and / or the surface mounting component of the printed circuit mounting board is melted again A method for soldering a printed wiring board or a printed circuit board , characterized by performing a reflow process for cooling and solidifying later.

In the method for soldering a printed wiring board or a printed circuit board according to the first aspect of the present invention, a printed circuit mounting board on which an electronic component once soldered in a flow furnace is loaded into a batch-type reflow furnace, for example, By heating the upper and lower nozzles and blowing hot air such as nitrogen gas, the entire mounting board is heated uniformly and the solder joints of the electronic component are melted again. Furthermore, since there is no means that in a reflow furnace in which the mounting plate is moved, for example, the mounting plate remains solder in a molten state is generally by injection cooling of the refrigerant from the upper and lower nozzle is uniformly cooled and solidified together. By mounting plate is uniformly cooled collectively, there is an advantage that it reduces the occurrence of lift-off occurrence and shrinkage cavity. Moreover, since the re-melted solder is rapidly cooled by using the rapid cooling medium, it becomes a solidified solder having a fine metal structure, so that soldering excellent in fatigue resistance can be obtained.

The printed wiring board or printed circuit board soldering method according to the second aspect of the present invention is the above-described solder joint portion in the printed wiring board or printed circuit board soldering method according to the first aspect of the present invention. In the reflow treatment heating step in which remelting is performed, the soldering atmosphere temperature is a melting point of the solder material + 5 ° C. or higher, and the temperature range of the insertion type electronic component to be soldered is −5 ° C. or lower. A method for soldering a printed wiring board or a printed circuit board .

In the soldering method of the printed wiring board or the printed circuit board according to the second aspect of the present invention, the function of the soldered electronic component is achieved by setting the ambient temperature to the minimum temperature at which the solder material can be maintained in a molten state. it is possible to prevent deterioration, and, since the temperature difference between the melting temperature and the solidification temperature is small, can be collectively uniformly because it is rapidly cooled and solidified, reducing the occurrence of lift-off occurrence and shrinkage cavity.

The printed wiring board or printed circuit board soldering method according to the third aspect of the present invention is the above-described printed wiring board or printed circuit board soldering method according to the first or second aspect of the present invention. Lead-free solder materials are Sn-Cu, Sn-Ag, Sn-Ag-Cu, Sn-Ag-Cu-Bi, Sn-Ag-Cu-Sb, Sn-Ag, which are basic solder materials mainly composed of Sn -Bi-In, Sn-Ag-In, Sn-Zn, Sn-Zn-Bi, Sn-Sb, and the basic solder materials include Al, Si, P, S, Ti, V, Cr, Mn, Fe , Co, Ni, Ga, Ge, As, Se, Zr, Nb, Mo, Pd, Hf, Ta, W, Pt, and any material selected from lead-free solder materials to which trace amounts are added With features A method for soldering a printed wiring board or a printed circuit board .
Since the lead-free solder can be used in the printed wiring board or the printed circuit board soldering method according to the third aspect of the present invention, the manufactured printed circuit board has little influence on the environment. .

  According to the present invention, after the flow soldering, the temperature distribution of the solder material in the individual solder joints and the substrate are obtained by performing reflow soldering in which the mounting circuit board is remelted and rapidly solidified without being conveyed in the furnace. The variation in the temperature distribution of the solder material in the whole can be reduced, so that the variation in the rapid cooling start temperature and the solidification time at each solder joint can be eliminated, and the occurrence of lift-off and the variation in fatigue life can be reduced. Can do.

  Further, in reflow soldering where remelting and rapid solidification are performed, the occurrence of lift-off can be effectively reduced by solidifying the solder by rapid cooling. In addition, the metal structure of the solidified solder material can be refined to improve the mechanical strength of the solder joint and reduce the variation in fatigue life.

  By reducing these problems, it is possible to improve the quality and reliability of the printed circuit board.

Hereinafter, an example of the soldering method according to the present invention will be described with reference to FIGS.
FIG. 1 is a flowchart of a soldering method according to the present invention. FIG. 2 is a flowchart of a conventional flow soldering method. A conventional flow soldering process 10 for a printed wiring board will be described with reference to FIG.

In step 11, a printed wiring board for mounting provided with circuit wiring such as a copper land and a copper through hole for soldering an electronic component is prepared. The printed wiring board for mounting may be either a single-sided board or a double-sided board. In this description, the printed wiring board is mounted with an insert component by flow soldering. You may mount by reflow soldering. Note that the same solder material is desirable as the solder material used when reflow soldering the surface mount component. And an insulating substrate of the printed wiring board, you are possible to use a glass epoxy substrate or a metal core substrate. Furthermore, a multilayer printed wiring board can also be used. In the next step 12, an insertion (package) type electronic component, for example, an electronic component with a lead terminal such as a relay, a capacitor, or a resistor is inserted and mounted in a prescribed through hole. A printed wiring board on which electronic components are mounted is set on a belt conveyor, and the electronic components that are transported and mounted on a flow furnace are flow soldered to the printed wiring board.

  First, in the flux application step 13, a flux for soldering is uniformly applied to the soldering surface of a printed wiring board on which electronic components are mounted. The printed wiring board on which the electronic components on which the flux has been applied is mounted is preheated to a preheating temperature, for example, 160 to 170 ° C., to activate the flux and improve the solderability in the preheating process 14, and the flow solder adheres. It is conveyed to step 15.

  In the flow solder attaching step 15, the flow solder is attached to the solder joint in a jet solder bath in which lead-free solder, for example, Sn-Ag-Cu-based lead-free solder is melted (250 ° C.). In addition, as a lead free solder, the lead free solder which has Sn as a main component, Preferably, Sn-Ag, Sn-Cu, Sn-Ag-Cu, Sn-Ag-Cu-Bi, Sn-Ag-Cu-Sb, Sn-Ag-Bi-In, Sn-Ag-In, Sn-Zn, Sn-Zn-Bi, Sn-Sb, and the above-mentioned alloys include Al, Si, P, S, Ti, V, Cr, Mn Fe, Co, Ni, Ga, Ge, As, Se, Zr, Nb, Mo, Pd, Hf, Ta, W, Pt, and Au may be added in minute amounts.

  The printed circuit mounting board (hereinafter referred to as a mounting board) on which the flow solder has been attached is cooled and solidified in the cooling and solidification step 16. The cooling method may be natural cooling, or may be cooled by immersion in a refrigerant liquid adjusted to a temperature selected in advance, or by spraying the refrigerant by gas injection, spraying, or showering.

  As a coolant for cooling the mounting board, air, water vapor, water, liquefied carbon dioxide (gas), liquefied nitrogen (gas), liquefied argon (gas), gas or liquid lower than the melting point of the solder material used, Liquefied helium (gas) can be used.

  If the mounting board is cooled and discharged and taken out from the flow furnace and the flow soldering is finished, if it is not a non-cleaning type flux, the attached soldering flux is cleaned and removed, and then the solder joint is visually inspected (process) 17) is performed, and a mounting board on which insertion type electronic components are mounted is completed.

  Next, the soldering method of this invention is demonstrated using FIG. The printed wiring board soldering process 1 of the present invention includes a flow soldering process 10 for manufacturing a mounting board by flow soldering a printed wiring board on which insertion type electronic components are mounted, and a mounting board manufactured in the process 10. And a reflow soldering step 20 for re-melting and rapidly solidifying the solder in the solder joint portion. Note that the reflow soldering here is not a solder plating or solder paste that has been applied in advance, which is used for soldering general surface mount components, but soldered solder joints. Remelting and rapid solidification of solder.

  The mounting substrate taken out of the flow furnace through the same steps (steps 11 to 16) as the flow soldering step 10 described above is immediately or when an intermediate step (step 17) such as a soldering appearance inspection is completed. The process proceeds to a reflow soldering step 20 in which the solder at the solder joint is remelted and rapidly solidified. The mounting board is transported to a reflow furnace 60 without a transport mechanism having a forced cooling mechanism that rapidly and uniformly cools the entire mounting board, for example, a batch-type reflow furnace, and placed at a predetermined position in the furnace (process) 21). 3 shows a batch-type reflow furnace 60, FIG. 3 (a) is a schematic view showing an outline of the reflow furnace 60 and a mounting substrate 50 mounted thereon, and FIG. 3 (b) shows a longitudinal sectional structure of the reflow furnace. It is a schematic diagram which shows the soldering state of the mounting board | substrate 50. FIG. FIG. 3A shows a state in which the mounting substrate 50 is supported in an end portion of the mounting substrate 50 by a support member (not shown) and placed in the reflow furnace 60. 3B shows a heating state and a cooling state of the mounting substrate 50 by the hot air heating method, and a heating nozzle 61 and a cooling nozzle 62 are arranged in the vertical direction of the mounting substrate 50. . The mounting substrate 50 is uniformly heated by hot air gas 61a ejected from the heating nozzle 61, for example, nitrogen gas preheated to a predetermined temperature by passing nitrogen gas through a space in which a heater (not shown) is installed. The temperature of the heating gas varies depending on the solder material used and the heat resistance of the component. For example, the lead-free solder material Sn-3.0Ag-0.5Cu (melting point: about 217 ° C.) is heated to about 250 ° C. Note that the reflow furnace 60 only needs to have a mechanism that can uniformly heat the entire surface of the plurality of mounted substrates 50 that are placed and can cool them uniformly. The atmosphere in the reflow furnace may be air, but is preferably a nitrogen atmosphere in order to prevent oxidation of solder, component lead terminals and the like. The heating method of the reflow furnace may be either a hot air heating method or an infrared radiation heating method, or a heating method in which both heating methods are combined.

  Note that the mounting board to which reflow soldering for remelting and rapid solidification is applied may be a mounting board in which surface mounting components and insertion type mounting components are mixed. Placed in a reflow furnace. Pre-treatment such as covering with a pallet to prevent heating or rapid cooling is performed on the mounting board on which surface mount components with low heat resistance or characteristics that deteriorate due to rapid cooling are mounted. Is done. The pre-processed mounting board is placed in the reflow furnace 60.

  As shown in FIG. 3B, the printed wiring board 51 of the mounting board 50 is heated at a predetermined temperature, and solder joints 55 (electronic component lead terminals 52a and copper lands 53, copper through holes 54). And the solder) are melted (step 22). The atmosphere temperature in the furnace at the time of remelting is higher than the melting point of the solder material, for example, the melting point of the solder + 5 ° C. or higher, and the heat resistance temperature of the mounted electronic component −5 ° C. or lower. Hot air 61a having an atmospheric temperature injected from the nozzle 61 is injected into the furnace, and the atmospheric temperature in the furnace rises and is obtained by reaching the temperature (atmospheric temperature) of the hot air 61a. The mounting substrate 50 is heated by the hot air 61a from the heating nozzle 61 and the ambient atmosphere gas. Further, the holding time at the time of remelting the solder is preferably a short time in which the copper erosion of the copper land is difficult to proceed and the wiring board and the mounted electronic component of the printed circuit mounting board 50 are not damaged by heat. Hold at melting point + 5 ° C. for 10 seconds.

  Similarly, the mounting substrate in which the surface mounting component and the insertion type mounting component are mixed is heated to a predetermined temperature and the solder at the solder joint is melted. In the surface mount component that is reflow soldered with the same solder paste as the lead-free solder used for soldering the insertion type mount component, the solder at the solder joint is melted by heating. However, the surface mount component is bonded and fixed to the substrate with a heat-resistant adhesive, and the surface mount component is not peeled off or moved by remelting heating.

  The mounting substrate 50 that has been cooled in the reflow furnace 60 is taken out of the reflow furnace 60, and an appearance inspection (step 24) of the solder joint is performed.

  When the surface temperature of the mounting substrate is lowered, the mounting substrate in which the surface mounting component and the insertion type mounting component are mixed is taken out from the reflow furnace 60, the jigs such as the pallet applied in the pretreatment are removed, and the solder joint portion is removed. Appearance inspection and the like are performed, and reflow soldering that rapidly solidifies after the solder joint is melted again is completed.

As described above, the mounting substrate 50 is manufactured by the flow soldering-reflow soldering which is remelted and rapidly solidified.

  Hereinafter, the effect of the soldering method of the present invention on the solder joint will be specifically described with reference to examples.

  After rapid cooling with the conventional flow furnace soldering (flow soldering) and rapid cooling with the flow furnace soldering of the present invention, the solder at the solder joint was remelted in a batch type reflow furnace. Cooled (reflow soldering) samples were prepared, and the effects of each soldering method (rapid cooling) on the generation of shrinkage nests and lift-off at solder joints were compared with the prior art and the present invention. It was.

  FIG. 4 shows a schematic diagram of a printed wiring board 70 on which electronic components are mounted. The printed wiring board 71 was a double-sided glass epoxy board (thickness: 1 mm, size: 150 mm square) provided with a copper land width of 0.5 mm and a copper through hole diameter of φ1.4 mm. Nine printed circuit board relays 72 (manufactured by OMRON: G8FE-1AP-L) were used as electronic components mounted on the printed wiring board 71. The material of the lead terminals of the relay 72 is copper, and the number of lead terminals is six / piece. The relay 72 is mounted on the board front part 71f, on the board center part 71c, on the board rear part 71r, and on the board rear part 71r with the transport direction (indicated by the arrow 75 in FIG. 4) of the flow soldering wiring board 71 as a reference. Three were installed. Six boards 70 on which relays 72 are mounted are prepared, and six sheets are subjected to rapid cooling flow soldering under the following conditions using conventional flow furnace soldering, and three of them are used as a conventional soldering sample. (Sample Nos. 1a to 3a). Using the batch-type reflow furnace equipped with a rapid cooling mechanism for the remaining three sheets, reflow soldering was performed for rapid cooling after remelting the solder joints under the following conditions of the present invention (Sample Nos. 1b to 3b). . As the solder material, lead-free Sn-3.0Ag-0.5Cu (melting point: about 217 ° C.) was used.

Flow soldering conditions: Conveyance speed: 1 m / min, solder jet temperature: 250 ° C.
Cooling rate: 10 ° C / second Reflow soldering conditions: Atmospheric temperature: 240 ° C, Holding time: 10 seconds
Cooling rate: 20 ° C./second Using a scanning electron microscope (SEM) on the solder joint portion (see FIG. 3B) 53 of each relay lead in the sample (mounting substrate) manufactured under the above-described soldering conditions Inspect the shrinkage nesting state and lift-off state by observation (use a magnification of 30 to 200 times as appropriate), and then check the lift-off by performing a cross-sectional inspection on the part that seems to be lift-off by surface observation. The number of shrinkage nests and the number of lift-off occurrences were calculated for 71f, the central part 71m, and the rear part 71r. The number of shrinkage cavities and the number of liftoff occurrences indicate the number of solder joints of the lead terminal where shrinkage cavities and liftoff are generated in the solder joints. The obtained results are shown in Table 1.

表1より、引け巣の発生数に関しては、各試料の検査はんだ接合部は５４ヶ所で、３試料の全検査はんだ接合部１６２ヶ所において、従来技術のはんだ付け方法の引け巣発生数は、３試料合計で４５ヶ所に対して、本発明の実施例１のはんだ付け方法の引け巣発生数は、３試料合計で６ヶ所と、従来技術のはんだ付け方法の1３％と非常に少なく、実装基板のはんだ接合部のはんだを再溶融、急冷凝固するリフローはんだ付けの効果が認められる。また、電子部品の搭載位置による影響は、各搭載位置の各試料の検査はんだ接合部は１８箇所で、３試料の全検査はんだ接合部５４ヶ所において、従来技術のはんだ付け方法における各部の引け巣発生数は、基板前部は合計１１ヶ所、基板中央部は合計１１ヶ所、基板後部は２３ヶ所である。最後に冷却される基板後部の発生数は他の位置の約２倍であり、電子部品の搭載位置によって引け巣の発生数にばらつきが生じている。これは従来技術のはんだ付け方法では、フローはんだ付けライン上を搬送しながら溶融はんだは冷却されて、基板前部、基板中央部、基板後部では、加熱温度、冷却速度等のはんだ付け条件が異なるためと考えられる。

From Table 1, regarding the number of shrinkage nests generated, 54 test solder joints of each sample were obtained, and at all 162 test solder joints of 3 samples, the number of shrinkage nests generated by the conventional soldering method was 3 Compared to 45 samples in total, the number of shrinkage cavities in the soldering method of Example 1 of the present invention is 6 in 3 samples, 13% of the conventional soldering method, which is very small. The effect of reflow soldering, which remelts and rapidly solidifies the solder at the solder joint, is recognized. In addition, the influence of the mounting position of the electronic component is that there are 18 inspection solder joints of each sample at each mounting position, and the shrinkage nests of each part in the conventional soldering method at 54 inspection solder joints of all three samples. The total number of occurrences is 11 at the front of the substrate, 11 at the center of the substrate, and 23 at the rear of the substrate. The number of occurrences of the rear part of the substrate that is finally cooled is about twice that of the other positions, and the number of shrinkage nests varies depending on the mounting position of the electronic component. In the conventional soldering method, the molten solder is cooled while being conveyed on the flow soldering line, and the soldering conditions such as the heating temperature and the cooling rate are different at the front part of the board, the central part of the board, and the rear part of the board. This is probably because of this.

  In the soldering method of Example 1 of the present invention, the number of shrinkage nests at each mounting position is 54 inspected, the total number of the front part of the board is two, the total number of the central part of the board is one, and the rear part of the board is three. The number of shrinkage nests is very small, and it cannot be said that there is an influence of the mounting position on the number of shrinkage nests. This is because the mounting board is not transported by the soldering method of the present invention, so the mounting position relationship with the front part of the board, the central part of the board, and the rear part of the board is lost, or the solder at the soldered joint is melted again. Since the entire substrate is uniformly cooled, it is considered that the number of shrinkage nests is small because the variation in the cooling rate is small.

  As described above, in the case of the conventional soldering method, the temperature of the jet solder that contacts the component mounting board during soldering, the substrate transport speed, the ambient temperature, the flow of the ambient gas, etc. Depending on the conditions, the molten solder state before the rapid cooling is not always kept constant, so that the soldering quality of the rapidly solidified mounting board varies.

  On the other hand, in the case of reflow soldering in which the solder of the solder joint portion of Example 1 of the present invention is remelted and rapidly solidified, rapid solidification is performed from a certain solder melting state, so that stable soldering quality is achieved. can get.

  As for the number of lift-off occurrences, the number of lift-off occurrences is zero for both the conventional soldering and the soldering of the present invention, the occurrence of lift-off is not observed, and there is no difference depending on the soldering method. From this, it was confirmed that the soldering method of the present invention has a sufficient effect of suppressing the occurrence of lift-off.

  Similarly to Example 1, after performing rapid cooling flow soldering by conventional flow furnace soldering and rapid cooling by flow furnace soldering of the present invention, soldering of solder joints in a batch-type reflow furnace A sample subjected to reflow soldering to be rapidly cooled after remelting was manufactured, and a comparative test according to the prior art and the present invention was conducted on the influence and effect of the difference in the soldering method on the fatigue life of the solder joint.

  In addition, the printed wiring board 70 and the mounting component 72 used the same thing as Example 1, and soldered on the same soldering conditions. Sample No. Since the soldering conditions were the same as in Example 1, the same numbers were assigned.

  The manufactured comparative test sample was placed in a thermostatic chamber capable of automatic temperature control, and a fatigue test was performed. The fatigue test is a cycle test with a temperature change from −40 ° C. to 140 ° C. The temperature profile in the thermostatic bath is maintained at −40 ° C. for 30 minutes → increased to 140 ° C. over 30 minutes → held at 140 ° C. for 30 minutes → decreased to −40 ° C. over 30 minutes. A 1000 cycle fatigue test was conducted.

  After the fatigue test, cross-sectional observation (a magnification of 30 to 200 times is used as appropriate) of each solder joint portion of the sample (mounting substrate to be tested) using a scanning electron microscope (SEM) The crack length was measured. Average values of the crack lengths of the measured substrate front portion 71f, substrate center portion 72m, and substrate rear portion 71r were derived. A sample in which a long crack is detected is a mounting substrate having a short life. Table 2 shows the results of the obtained solder crack length.

表２より、従来技術のはんだ付け方法によるはんだき裂長さ（全平均値６６７μｍ）よりも、本発明の実施例２のはんだ付け方法のはんだき裂長さ（全平均値４６１μｍ）は、約２００μｍ小さくなっている。また、従来技術のはんだ付け方法における各部の平均はんだき裂長さは、基板前部７１ｆは６１０μｍ、基板中央部７１ｍは６２７μｍ、基板後部７１ｒは７６０μｍである。最後に冷却される基板後部７１ｒのはんだき裂長さは他の位置７１ｆ、７１ｍよりも約１５０μｍ長く、電子部品の搭載位置によってはんだき裂長さに差異が生じている。これは従来技術のはんだ付け方法では、部品搭載基板は噴流はんだ槽でのはんだ付着後、フローはんだ付けライン上を搬送されながら周囲の条件（基板の搬送速度、雰囲気温度、雰囲気ガスの流れ等）に応じて冷却されて、基板前部７１ｆ、基板中央部７１ｍ、基板後部７１ｒでは、急冷凝固前の条件が異なる。そのため、はんだ接合部のはんだ凝固組織のＳｎ結晶粒のサイズは異なり、はんだき裂長さ（寿命）にばらつきが発生する。

From Table 2, the solder crack length (total average value 461 μm) of the soldering method of Example 2 of the present invention is about 200 μm smaller than the solder crack length (total average value 667 μm) of the conventional soldering method. It has become. Moreover, the average solder crack length of each part in the soldering method of the prior art is 610 μm for the substrate front portion 71 f, 627 μm for the substrate center portion 71 m, and 760 μm for the substrate rear portion 71 r. Finally, the solder crack length of the board rear portion 71r to be cooled is approximately 150 μm longer than the other positions 71f and 71m, and the solder crack length varies depending on the mounting position of the electronic component. This is a conventional soldering method, in which the component mounting board is transported on the flow soldering line after soldering in the jet solder bath, and the ambient conditions (board transport speed, ambient temperature, ambient gas flow, etc.) Accordingly, the substrate front portion 71f, the substrate center portion 71m, and the substrate rear portion 71r have different conditions before rapid solidification. Therefore, the size of the Sn crystal grains in the solder solidified structure of the solder joint is different, and variation occurs in the solder crack length (life).

    In the soldering method of Example 2 of the present invention, the average solder crack length at the component placement position is 450 μm for the substrate front portion 71f, 457 μm for the substrate center portion 71m, 470 μm for the substrate rear portion 71r, and the solder crack length is It is smaller than the solder crack length of the prior art soldering, and the variation is small. In the soldering method according to each embodiment of the present invention, the mounting board is not transported, so that the mounting position relationship of the components of the board front part 71f, the board center part 71m, and the board rear part 71r is lost. In the soldering method of the present invention, after the solder at the solder joint is melted again, the entire board is rapidly and uniformly cooled under the optimum conditions without transporting the board. And a uniform solder solidification structure can be obtained, and as a result, variation in solder crack length (life) is reduced.

It is a flowchart of the soldering method in this invention. It is a flowchart of the conventional flow soldering method. 3 shows the soldering state of the batch-type reflow furnace 60, FIG. 3 (a) is a schematic view showing the outline of the reflow furnace 60 and the mounted substrate 50, and FIG. 3 (b) shows the reflow furnace. It is a schematic diagram which shows the soldering state of a longitudinal cross-section structure and the mounting substrate 50. FIG. The schematic diagram of the printed wiring board 70 carrying an electronic component is shown.

Explanation of symbols

1: Soldering process of printed wiring board of the present invention 10: Flow soldering process 13: Flux application process 14: Preheating process 15: Jet soldering process 16: Cooling process 20: Reflow soldering process 21: Solder remelting process 22 : Rapid cooling and solidification process 50: Mounting board 51: Printed wiring board 52: Insertion type electronic component 52a: Lead terminal 53: Copper land 54: Copper through hole 55: Solder joint 60: Reflow furnace 61: Nozzle for heating 62: Cooling Nozzle 63: Heating pipe 64: Cooling pipe 70: Electronic component-mounted printed wiring board 71: Printed wiring board 71f: Board front 72m: Board center 72r: Board rear 72: Relay 75: Board transport direction

Claims (3)

In a soldering method of a printed circuit board on which a printed wiring board or a surface mount component is mounted using a lead-free solder material, an insertion type electronic component is inserted into the through hole of the printed wiring board or the printed circuit board, and flow soldering is performed. The printed circuit mounting board on which the insertion type electronic component is mounted is manufactured by, and then the printed circuit mounting board is placed in a heating furnace and arranged in the vertical direction of the printed circuit mounting board inside the heating furnace. After heating the printed circuit board using hot air blown from the heating nozzle to the range including the entire surface of the printed circuit board, the printed circuit board is disposed in the vertical direction inside the heating furnace. by cooling the printed circuit mounting board from the cooling nozzle by utilizing the refrigerant ejected to the range including the entire surface of the printed circuit mounting board, the Soldering of printed circuit boards or printed circuit board and performing reflow process to cool solidifying the solder of the insertion type solder joints of the electronic components and / or surface mount component of lint circuit mounting board was melted again Method. Ambient temperature during solder melting in the reflow process of heating step of melting the solder joint again, a melting point of + 5 ° C. above the temperature of the solder material, the insertion type heat resistant temperature -5 ° C. of an electronic component soldered soldering method for a printed wiring board or printed circuit board according to claim 1 which is within the following temperature ranges. The lead-free solder materials are Sn—Cu, Sn—Ag, Sn—Ag—Cu, Sn—Ag—Cu—Bi, Sn—Ag—Cu—Sb, Sn—, which are basic solder materials mainly composed of Sn. Ag-Bi-In, Sn-Ag-In, Sn-Zn, Sn-Zn-Bi, Sn-Sb, and the basic solder materials include Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Ge, As, Se, Zr, Nb, Mo, Pd, Hf, Ta, W, Pt, and any material selected from lead-free solder materials to which trace amounts of Au are added soldering method for a printed wiring board or printed circuit board according to claim 1 or claim 2, characterized in that.

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