JP2005142209A - Electronic circuit device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an electronic circuit device which can be used without troubles over a long period of time, even when it is subjected to stresses caused by severe heat cycles so as to surely maintain media which have become necessary infrastructures in one's lives. <P>SOLUTION: A plurality of electronic parts are soldered to constitute an electronic circuit, and the electronic circuits are assembled into the electronic circuit device which is so constituted as to be carried with a user as it is held, for instance, in the pocket. The soldered joints of the electronic circuit device are soldered with solder whose main components are tin and zinc. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electronic circuit device that can extremely reduce the occurrence of a failure even under severe heat cycles.

  Changes in lifestyle such as outdoor use and the emergence of seamless and ubiquitous information networks require electronic circuit devices such as communication devices, information processing devices, and AV devices to simultaneously reduce size, increase speed, and increase output. Furthermore, it came to ask for tolerance to the drastic change of the use environment.

  As a result, the increase in power consumption per unit volume in the electronic circuit device, and consequently, the amount of generated heat increases dramatically, causing an extreme temperature rise. Moreover, the temperature change of the use environment has become larger than before, and the number of fluctuations has become extremely frequent.

  For example, high-speed processors are difficult to operate without forced cooling because the processor itself is thermally damaged by self-heating, and forced cooling is even a use condition. Of course, the same applies to power semiconductor elements that require cooling.

  In addition, electronic circuit devices that are carried outdoors and used frequently shift to environments with intense greenhouse effects such as holding in clothes, direct sunlight, and leaving them in vehicles with sunlight. Repeated exposure to environment and heating environment.

  Thus, electronic circuit devices in recent years are required to operate without failing even under severe heat cycle conditions as compared with conventional ones. Of course, this is also required for electronic components used in electronic circuit devices, but also for the connection reliability of the soldering parts necessary to form electronic circuits by connecting electronic components to each other. It has been demanded.

  FIG. 1 is a view showing a longitudinal section in a state where electronic components used in an electronic circuit device are soldered and fixed to a printed wiring board, where (a) shows a normal state and (b) shows It is a figure which shows the state which produced the crack in patterns, such as a land and a through hole, by the heat cycle stress.

  That is, in the electronic component, the lead terminal 4 is connected and fixed to the land 2 of the printed wiring board 1 that is a fixing member via the solder 5, and constitutes a connection portion, that is, a soldering portion. More specifically, the lead terminal 4 of the electronic component is inserted into the through hole 3 of the printed wiring board 1, and a soldered portion is formed between the through hole 3 and the land 2 connected to the through hole 3. By the wetting by 5, a soldering portion in which these are electrically and mechanically connected to each other is formed.

  The thermal energy generated in the electronic component by energization in addition to the temperature change of the usage environment appears as a temperature rise of the electronic component, and raises the temperature of the soldering portion through the lead terminal. Usually, the maximum operating temperature of an electronic component is defined by the junction temperature of an electronic component such as a semiconductor element, the allowable power of a resistor, and the temperature of a capacitor, a coil, or the like. The environmental temperature to be used is also specified.

  For example, if the amount of heat generated by the electronic component is large, the temperature rise inside the electronic component also increases, the temperature of the lead terminal increases, and the temperature of the soldering portion also increases greatly. Incidentally, an electrical good conductor used for a lead terminal of an electronic component is usually a good conductor for heat conduction.

  In addition, even when the electronic circuit device is not in operation, the temperature of the electronic circuit device carried by the portable electronic circuit device is maintained in the clothes received, and the temperature rises due to solar radiation. The temperature of the electronic component and the soldering portion repeatedly rises and falls due to a rise in temperature or a decrease in temperature due to the reverse cooling environment, a temperature change caused by reciprocating passage between the cold environment and the heating environment in winter. Therefore, if the electronic circuit device is operated in such an environment, as described above, the temperature rise due to its own heat generation is further added, and the temperature change is further expanded.

  On the other hand, today, electronic circuit devices are required to be simultaneously reduced in size, speeded up, and increased in output, resulting in an increase in power consumption per unit volume of electronic components. It has become extremely large. In addition, as electronic parts are miniaturized, the volume of the soldered portion is extremely reduced, and as the heat capacity is reduced, temperature increases and temperature drops are easily generated. In other words, the temperature rises or falls with a high sensitivity following the temperature rise or temperature drop of the electronic component, or the temperature rise and the temperature fall repeatedly with a sensitive follow-up of the environmental temperature change.

  Here, as a prior art, there is one that provides an electrical / electronic component suitable for joining and assembling with lead-free solder (see Patent Document 1). This Patent Document 1 contains tin, an alloy-forming metal selected from the group consisting of zinc, silver and copper, and the proportion of the alloy-forming metal in the precoat is 3 wt% or less.

  As another conventional technique, there is a technique in which a printed wiring board is precoated with tin-silver solder and soldered with tin-silver-copper solder (see Patent Document 2). In Patent Document 2, tin-zinc solder is avoided because it has low wettability.

  Furthermore, as another conventional technique, there is a technique related to a solder whose characteristics are improved by adding nickel, silver, copper, bismuth, indium, and phosphorus to tin-zinc solder (see Patent Document 3).

However, none of these conventional techniques have found the excellent characteristics of tin-zinc solder from the viewpoint of resistance to heat cycle stress.
JP 2001-284785 A JP 2003-069214 A JP 09-094688 A

  The lifetime of an electronic circuit device is at least 7 years even if it is a consumer product, considering the life cycle of the device and the storage period of maintenance parts. Of course, most electronic circuit devices produced in Japan have a lifetime of more than 10 years, coupled with the technical excellence. And tin-lead solder has been used there.

  However, the diffusion of lead poison into the natural environment and the effect on the human body has become a problem, and lead-free solder that does not use lead has been used for soldering electronic circuit devices. At present, tin-silver-copper lead-free solder, tin-copper lead-free solder, and tin-silver lead-free solder are often used.

  However, these lead-free solders that have been widely used in recent years have serious problems in the soldering parts that are the constituent elements due to the heat generated in the electronic circuit device itself or the above-described heat cycle received from the environment. Has been found to generate.

  That is, as shown in FIG. 1 (b), the land is peeled off due to heat cycle stress, and the land or the through hole is cracked to cut the circuit, so that the electronic circuit becomes inoperable. Note that the state shown in FIG. 1B is caused by heat cycle stress and is different from lift-off.

  The occurrence of land peeling and cracks due to such heat cycle stress is mainly due to mismatching of thermal expansion coefficients between members constituting the soldering portion of the electronic circuit device.

  For example, the most commonly used FR-4 glass epoxy substrate has a thermal expansion coefficient in the plate surface direction of about 13 to 16 ppm · K−1, and the thermal expansion coefficient in the thickness direction is 55 ppm · K below the glass transition temperature Tg. -1 and about 250 ppm · K-1 above the glass transition temperature Tg. On the other hand, the solder is about 20 ppm · K-1, and the copper used as the wiring pattern is about 18 ppm · K-1.

  FIG. 2 shows a soldering mounting using a tin-3silver-0.5 copper solder (meaning a solder composed of 3% by weight silver, 0.5% by weight copper and the balance tin). In an electronic circuit device, it is the figure which calculated | required the relationship between the number of heat cycles and the crack generation accompanying circuit cutting.

  2A shows a case where a preflux is applied to the copper surface as a land or a through hole of the printed wiring board, and FIG. 2B shows a tin-silver-copper on the copper surface of the land or the through hole of the printed wiring board. The case where the HAL process by a system solder is given is shown. On the other hand, as a kind of plating of lead terminals of electronic components mounted on these printed wiring boards, tin plating, tin-lead solder plating, nickel plating, or further plating palladium on the nickel layer (nickel / palladium plating) The thing was tested. One heat cycle was set to −40 ° C. to 125 ° C. in 30 minutes.

  As can be seen from the figure, in an electronic circuit device using a tin-silver-copper-based lead-free solder, the soldering part is cracked or peeled off in a heat cycle of about 400 cycles, causing the electronic circuit device to fail. It becomes. This corresponds to 4.5 years assuming that a heat cycle from 0 ° C. to 60 ° C. is applied once a day (Manson-Coffin rule).

  On the other hand, as an electronic circuit device in which the usage environment changes most frequently, there is a device that can be carried around and held in a user's clothes or moss. For example, a mobile phone device, a portable audio device, a PDA device, an electronic database device (electronic dictionary), a broadcast receiving device, a licensed wireless communication device, a hearing aid device, an electronic camera device (digital camera), a video camera (video camera) ) Etc.

  These devices are kept warm in clothing and moss, and are exposed to high temperature environments exceeding 60 ° C. due to solar radiation. It may also be directly exposed to solar radiation. Furthermore, when left in a vehicle parked in a solar radiation state, it is exposed to a high temperature exceeding 90 ° C. And the temperature rise accompanying operation | movement is further weighted.

  In addition, these devices are exposed to a cold environment of 0 ° C. or lower in winter, transition to a heating environment of about 30 ° C. when entering a heating environment, and further exposed to a temperature of 40 ° C. or higher if held in clothing. Sometimes it is done.

  In addition, such an electronic circuit device is generally provided with an input instruction operation means, that is, a switch or the like, and is also exposed to the stress and impact associated with the keystroke of the switch. From impact to impact, etc., one after another, it is exposed to severe stress conditions that are weighted together with the heat cycle stress described above.

  In addition, various control devices used in vehicles, broadcast receiving devices, audio devices, GPS devices, ETC devices, and the like are exposed to a heat cycle due to a rise in engine temperature or a heat cycle due to indoor air conditioning for each operation. In addition, outside of operation, it is exposed at least once a day to a temperature change, i.e., a heat cycle, between the night temperature and the temperature exposed to daytime solar radiation.

  If you look at home, if you think that it is used 2-3 times a day (morning and night or noon) in daily life electronic circuit devices such as TV devices (especially CRT type TV), At least heat cycle is applied 2-3 times a day. In addition, the high power circuit that drives the CRT becomes extremely hot, and the temperature of the soldered portion and thus the temperature of the solder exceeds 80 ° C. Therefore, a heat cycle of 20 ° C. to more than 80 ° C. is applied to the soldering part 2 to 3 times a day. That is, the temperature in a TV device (CRT type TV) or CRT monitor device related to AV, IT, etc. is about 20 to 30 ° C. higher than the ambient environment temperature, and the lead terminal temperature of an electronic component that generates a large amount of heat. Is further increased by 50 to 60 ° C. or more.

  A power element of an electronic circuit device that handles a large amount of power such as various power supply devices, power amplification devices, and power control devices generates a large amount of heat loss, and increases the temperature of the soldering portion as the temperature of the device itself increases. It is not uncommon for recent high-power semiconductor devices to be used at a junction temperature of about 90 ° C., and the temperature of the lead terminals, connection terminals, and soldered portions thereof exceeds 70 ° C.

  The same applies to other electronic circuit devices although there is a difference in the heat cycle. General-purpose high-speed processors consume several tens of watts of power on a single chip, and recently, personal computers using water cooling have been introduced to secure the amount of heat exhaust.

  Among the electronic circuit devices described above, the electronic circuit device that is most susceptible to the harsh heat cycle is transported while being held by a user's clothes, bag, etc., and can be used anywhere. This is an electronic circuit device.

  Therefore, in these electronic circuit devices, a tin-silver-copper lead-free solder or a tin-copper lead-free solder is used in order to prevent the occurrence of cracks accompanying circuit cutting as shown in FIG. In the electronic circuit equipment that uses, the size and shape of the land of the printed wiring board, which is a fixing member of the electronic component, is changed in mounting design, the adhesive strength of the land and wiring pattern is improved, or the solder resist is used around the land. Measures to improve strength, such as covering a part of the body, have been started. However, this requires a large-scale work to revise a conventional design standard (design standard).

  Therefore, an object of the present invention is to realize an electronic circuit device that can be used for a long period of time without being damaged even under severe heat cycle stress. It is to ensure that it can be maintained.

  The present invention is characterized in that a stress-resistant electronic circuit device is configured so that a very good soldering connection can be maintained against heat cycle stress.

  Specifically, in the first aspect of the present invention, in an electronic circuit device configured on the assumption that a plurality of electronic components can be soldered to form an electronic circuit and can be held in a user's clothes, The soldering portion of the circuit device is an electronic circuit device configured to be soldered with solder mainly composed of tin and zinc.

  Soldered parts with tin and zinc as the main component can directly damage the soldering lands and through-holes of printed circuit boards that make up electronic circuit devices even when heat cycle stress is applied. There is no. Therefore, cracks that lead to circuit cutting do not occur in the soldering lands and through holes.

  Further, in the second aspect of the present invention, when the electronic circuit is configured by soldering a plurality of electronic components, the electronic components are soldered due to the self-heating of the electronic components or the temperature change of the usage environment. In an electronic circuit device that undergoes a heat cycle with a temperature difference of 60 ° C. or more at a temperature of the soldering portion, the soldering portion of the electronic circuit device is configured to be soldered with a solder mainly composed of tin and zinc. An electronic circuit device.

  When tin-silver-copper-based lead-free solder is used in an electronic circuit device that undergoes a heat cycle at a temperature difference of 60 ° C. or more, cracks that lead to circuit disconnection are likely to occur in soldered lands and through holes in several years. By soldering with a solder mainly composed of tin and zinc, they are eliminated, and a life exceeding the generally required device life can be obtained.

  Furthermore, in the third aspect of the present invention, in the first aspect or the second aspect, the surface of the member to which the electronic component is soldered and fixed has a tin content of 90% by weight or more. The electronic circuit device is configured so that the surface thereof is preliminarily formed of tin-rich lead-free solder, and the electronic component and the member are soldered using a solder mainly composed of tin and zinc.

  In this way, by forming tin or tin-rich lead-free solder with a tin content of 90% by weight or more in advance on the surface of the part to be soldered, the solder mainly composed of tin and zinc wets and spreads. It becomes easy. Furthermore, it becomes possible to obtain a good soldered portion having excellent wettability, and an electronic circuit device having a strong resistance to heat cycle stress can be realized.

  According to the electronic circuit device of the present invention, it is possible to realize an electronic circuit device that can be used without a failure for a long period of time even under severe heat cycle stress. It will be possible to reliably maintain the old media.

  The electronic circuit device of the present invention can be realized in the following embodiments. That is, a large number of electronic components constituting each element of the electronic circuit are soldered and mounted on a printed wiring board by a known flow soldering method or reflow soldering method, thereby forming a target electronic circuit.

  When this soldering mounting is performed using a printed wiring board that has been subjected to HAL treatment with tin such as tin-zinc solder or lead-free solder containing 90% or more of tin, the best solder wettability can be obtained.

  As for the types of soldering lead terminals and soldering terminals for electronic parts, in addition to the plating of lead-free solder containing 90% or more of tin or tin, similar to the HAL treatment, tin-lead solder plating or nickel / Palladium plating can be used.

  In addition, as a solder used for this soldering mounting, it is possible to use a tin-9 zinc solder or a solder containing tin and zinc as main components and a small amount of elements for improving characteristics such as bismuth, indium, and aluminum. it can. In other words, the present invention is characterized in that the solder is tin-9 zinc solder or solder containing at least one of bismuth, indium or aluminum containing tin and zinc as main components.

  On the other hand, the soldering temperature can be employed in the range of 210 ° C. to 250 ° C., and sufficient solder wettability can be obtained even at a low temperature of about 230 ° C., for example. In addition, when performing flow soldering, soldering may be performed in an inert gas atmosphere having a low oxygen concentration. Also, reflow soldering is better performed in an inert gas atmosphere with a low oxygen concentration. By performing the soldering and mounting operation in such an inert gas atmosphere with a low oxygen concentration, oxidation of the soldered portion and the solder is suppressed, and a more excellent solder wettability can be obtained.

  FIG. 3 is a diagram showing the relationship between the number of heat cycles and the occurrence of cracks accompanying circuit cutting in an electronic circuit device that has been soldered and mounted using tin-9 zinc solder. 3A shows the relationship when the soldering temperature is 250 ° C., and FIG. 3B shows the relationship when the soldering temperature is 230 ° C.

  The printed wiring board used for this test is a printed wiring board obtained by leveling tin-9 zinc solder by HAL treatment. Then, tin-lead solder, nickel / palladium, and tin-bismuth were used as the types of plating for soldering lead terminals or soldering terminals of electronic components to be soldered and mounted.

  In addition, in the thing using tin-bismuth, the thing of a copper base material and the thing of an iron base material (42Alloy) were used as a base material of a terminal. In the heat cycle, both the high temperature side and the low temperature side had a holding time of 30 minutes and a room temperature exposure time of 5 minutes to −40 ° C. to 125 ° C.

  As can be seen from the figure, cracks with circuit cutting occurred in 900 cycles only when using soldered lead terminals or soldered terminals plated with tin-bismuth plating with iron as the base material, but everything else The electronic circuit was kept normal against 1000 cycles of heat cycle stress.

  This number of 900 cycles corresponds to 13.7 years assuming that a heat cycle of 0 ° C. to 60 ° C. is applied once a day (Manson-Coffin rule). That is, it becomes possible to realize an electronic circuit device having a very long life against such intense heat cycle stress.

  In order to analyze such a long-life soldering portion, the inventors analyzed the state of the soldering portion after applying 1000 cycles of heat cycle stress. 4A and 4B are views showing a vertical cross section, in which FIG. 4A shows a state in which the tip of the fillet is deviated, and FIG. 4B shows a state of divergence occurring around the through hole.

  That is, it can be seen that although there is a partial divergence between the tin-zinc solder and the copper-zinc alloy layer, the stress that causes the divergence does not cause cracks in the copper-zinc alloy layer, lands, and through holes. This is considered to be due to the fact that the copper-zinc alloy layer has a protective effect because it is harder than the other members.

  By the way, such divergence does not break the printed circuit board lands, through-holes, and circuit patterns, so the solder is melted by reheating (for example, heating and melting by bringing a solder iron into contact). It is possible to solve this problem, and it can be easily recovered by simple repair work.

  Thus, the electronic circuit device of the present invention can exhibit extremely excellent reliability against severe heat cycle stress. That is, as described above, the mobile phone device and the mobile audio device, the PDA device, the electronic database device (electronic dictionary), the broadcast receiving device, the license grant type wireless communication device, the auditory sense, and the usage environment change most frequently. Electronic circuit devices such as auxiliary devices, electronic camera devices (digital cameras), video photographing devices (video cameras), etc. will not easily fail.

  These electronic circuit devices are frequently exposed to high temperature environments exceeding 60 ° C. in use, and in some cases, they are also frequently exposed to high temperatures exceeding 90 ° C. Moreover, this temperature is not constant, and is added as a heat cycle that reciprocates between a temperature of about room temperature. In the severe winter season, the most severe heat cycle stress is easily applied.

  In addition, the stress and impact associated with the keystroke of the switch, the impact of placing an electronic circuit device on a table, the impact of a collision, etc. are received from one to the next, and are exposed to severely stressed conditions. Yes.

  However, the electronic circuit device according to the present invention can withstand such a severe use condition, and can obtain long-term reliability that is well beyond the obsolete period of the performance of the electronic circuit device. become. Moreover, it is not necessary to change the design standard (design standard) of the wiring pattern that has been used in the past, and there is no cost increase, and it is possible to design an electronic circuit device with the same design rules as before. it can.

(A) is sectional drawing of the vertical direction of the state by which the electronic component was soldered and fixed to the printed wiring board, (b) is sectional drawing of the land peeling and pattern disconnection example which generate | occur | produced by the heat cycle stress. It is the figure which calculated | required the relationship of the crack generation | occurrence | production with the number of heat cycles and circuit cutting | disconnection in the electronic circuit apparatus which soldered and mounted using the tin-3 silver-0.5 copper solder. It is the figure which calculated | required the relationship of the crack generation | occurrence | production with the number of heat cycles and circuit cutting | disconnection in the electronic circuit apparatus which performed soldering mounting using the tin-9 zinc solder. It is the longitudinal cross-sectional view which analyzed the state of the soldering part after applying the heat cycle stress of 1000 cycles, (a) shows the state from which the fillet front-end | tip part separated, (b) is produced around a through hole Shows the state of divergence.

Explanation of symbols

1 Printed Wiring Board 2 Land 3 Through Hole 4 Lead Terminal 5 Solder 6 Fillet

Claims (6)

In an electronic circuit device configured such that a plurality of electronic components are soldered to form an electronic circuit and can be held on a user's clothes,
The electronic circuit device according to claim 1, wherein the soldering portion of the electronic circuit device is configured by soldering with a solder mainly composed of tin and zinc. The surface of the member to which the electronic component is soldered and fixed is preliminarily composed of tin or tin-rich lead-free solder having a tin content of 90% by weight or more. The electronic circuit device according to claim 1, wherein the electronic circuit device is configured by soldering using solder containing zinc and zinc as main components. 2. The electronic circuit device according to claim 1, wherein the solder is tin-9 zinc solder or solder containing at least one of bismuth, indium, and aluminum containing tin and zinc as main components. When a plurality of electronic components are soldered to form an electronic circuit, the temperature of the soldered portion where the electronic components are soldered is 60 ° C. or higher due to self-heating of the electronic components or temperature changes in the usage environment. In an electronic circuit device that undergoes a heat cycle with a difference,
The electronic circuit device according to claim 1, wherein the soldering portion of the electronic circuit device is configured by soldering with a solder mainly composed of tin and zinc. The surface of the member to which the electronic component is soldered and fixed is preliminarily composed of tin or tin-rich lead-free solder having a tin content of 90% by weight or more. The electronic circuit device according to claim 4, wherein the electronic circuit device is configured by soldering using a solder composed mainly of zinc and zinc. 5. The electronic circuit device according to claim 4, wherein the solder is tin-9 zinc solder or solder containing at least one of bismuth, indium, and aluminum containing tin and zinc as main components.