JP2006310619A - High-frequency circuit module and its mounting structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency circuit module which can be mounted on a circuit board with suppressed connection loss by using BGA (Ball Grid Array), and also to provide a mounting structure of the same. <P>SOLUTION: The high-frequency circuit module 10 includes a dielectric substrate having a waveguide terminal 7 and the BGA formed on a plurality of electrode pads 5. The BGA consists of composite solder balls 3a, each consisting of a solder ball 3b, a core 15 which hardly deforms by the dead weight of the high-frequency circuit module at the time of reflow mounting, and a solder layer 13 which coats the core 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-frequency circuit module having a built-in high-frequency semiconductor element such as a microwave and a millimeter wave and controlling the power line, signal line, waveguide, high-frequency line, etc. It is.

  High-frequency circuit modules in the millimeter wave and microwave bands used for commercial communication devices, artificial satellites, radars, etc. must have high reliability and long life. For this reason, the high-frequency circuit module is a hollow hermetic seal that uses metal, ceramic, or a combination of both for the purpose of protecting built-in semiconductor elements, ensuring airtightness, blocking electromagnetic wave leakage, blocking external interference, etc. Used in modules.

  In order to input and output high-frequency electrical signals from these high-frequency circuit modules, two systems are roughly classified. One is a feed-through structure that inputs and outputs signals to the high-frequency circuit module with the microstrip line, and the other is once converted to the waveguide mode by the waveguide converter via the microstrip line. In this method, the light is guided outside the high-frequency circuit module through the waveguide.

  In the latter case, the waveguide is, for example, provided on the printed circuit board outside the high-frequency circuit module, using a waveguide structure filled with a dielectric material in order to ensure airtightness in the wiring board portion inside the high-frequency circuit module. A hollow waveguide made of metal is used. These waveguides are used by connecting the inner part of the high-frequency circuit module and the outer part of the high-frequency circuit module. As a connection method, it is used by being screwed through a metal frame or the like attached by a known method. That is, a high-frequency circuit module used at a high frequency needs to be fastened with screws.

  However, the structure of the above screw fastening becomes large, and it is difficult to use because the screw fastening needs to be performed in a process different from the mounting of other components. It has become a hindrance to downsizing, downsizing, and weight reduction. In order to solve this problem, recently, a method has been proposed in which a BGA (ball grid array) structure is applied and the both are connected in a form of surface mounting on a printed circuit board (see Patent Document 1).

In the connection structure of the high-frequency circuit module using the BGA, a waveguide terminal, a signal terminal, a control signal terminal, a ground terminal, and a bias terminal are arranged on the lower surface (back surface or bottom surface) of the multilayer dielectric substrate constituting the high-frequency circuit module. . Further, electrode pads are also arranged on the upper surface of the circuit board on which the high frequency circuit module is mounted so as to correspond to the electrode pads of the high frequency circuit module. And mounting is realized by connecting all corresponding terminals with solder balls. Such a type of high-frequency circuit module has an attractive structure in terms of cost, productivity, and the like such that it can be mounted on a circuit board at the same time by applying reflow mounting.
JP 2004-254068 A

  Surface mounting by BGA has rapidly spread in recent years because it has many features such as a small mounting area and the ability to increase the number of pins in a limited area. (1) Solder balls are deformed during mounting, and (2) There are problems such as difficulty in connection inspection after mounting.

  The problem of the deformation of the solder ball at the time of mounting (1) is as follows. When performing surface mounting using a BGA, the deformation of the solder ball is not a major problem when mounting a lightweight package such as a plastic package frequently used in ordinary electronic equipment. However, in a high-frequency circuit module that uses a large amount of material such as ceramic or metal and has a large weight, deformation of the solder ball is a serious problem related to the success or failure of the mounting.

  For example, when reflow mounting a high-frequency circuit module that has a gap between the geometric center of the module and the center of gravity of the module, there is a problem that when the solder melts, the balance is lost and the device is mounted while being tilted ( Tilt implementation). When such deformation occurs during mounting, the distance (standoff) between the high-frequency circuit module and the circuit board and the distance d between the solder balls change. When such a change occurs in the waveguide circuit section, a connection loss occurs, and if this changes for each high-frequency circuit module, it interferes with the manufacture of a uniform product.

  On the other hand, even when the mounting is performed normally, the spherical solder ball is deformed by the dead weight of the high-frequency circuit module when the solder is melted, and becomes a flat sphere having an elliptical cross section. In an extreme case, the distance d between the adjacent solder balls is shortened, and a phenomenon of contact with the adjacent solder balls and integration (d ≦ 0), that is, a solder bridge (solder bridge connection) occurs. There was a problem that occurred. When the solder bridge connection is generated at the signal terminal, the control signal terminal, the ground terminal and the bias terminal, the high frequency circuit module does not operate normally.

  In addition, the problem (2) that the connection inspection after mounting is difficult is as follows. This is not limited to a high-frequency circuit module, but BGA is generally a problem that it is difficult to inspect a connection part after being mounted on a circuit board. That is, since the following defects may occur in mounting using solder balls, sampling or the total number of X-ray inspections is usually performed. When BGA mounting is performed, circuit open connection (gap formation), short circuit (solder bridge connection), and the like occur. Further, as described above, there is a possibility that tilt mounting occurs due to deformation of the solder balls.

  Among the above, the phenomenon in which the circuit module is mounted at an inclination is regarded as a non-defective product in a normal electronic device as long as the circuit function is not hindered. However, the high-frequency circuit module is defective because the connection loss occurs in the waveguide circuit as described above.

  In addition to the above improper implementation, "snowman (visually distinguishable connection between the head and torso)" or "mirror fence (visually distinguishable connection between the upper and lower flats) There is an incomplete joint described as “. It is said that the reason why the “snowman” type defect occurs is that the solder balls and the solder paste supplied to the circuit board are not completely mixed in the surface mounting process due to moisture, oxide film, and the like. The problem is that, in spite of such a mounting state, there is a case where electrical conduction is caused by the incomplete joint. For this reason, even if the connection reliability is significantly lowered, unless it is confirmed by an image, it is difficult to detect by electrical inspection.

  Defects associated with the BGA mounting described above must be detected before the product is shipped. The inspection is not so difficult because the outermost ball row can be detected by visual observation or the like, but it is not easy to detect the innermost ball row than the outermost ball row.

  Usually, inspection using X-rays is widely performed. In X-ray inspection, solder bridges can be easily detected, but are difficult to detect for open connections (gap formation) and snowball failures (incomplete joints). In addition, in a high-frequency circuit module that often uses a ceramic substrate, there is a problem that observation with high resolution is not possible because the metal material and the inner layer wiring interfere.

  In addition, open connections (gap formation) can be detected by electrical inspection methods such as boundary scan, but as described above, electrical inspection methods prevent snowball failures (incomplete joints). Can not respond. A three-dimensional inspection method using X-ray CT or the like may only be able to cope with this incomplete bonding problem. However, X-ray CT has problems in processing time, cost of an inspection apparatus, and the like, and is difficult to say as a general technique. That is, the cost is increased due to the complexity of the process, the time required for the test, and the time and effort, so that the feasibility is poor.

  The high-frequency circuit module needs to suppress the power loss (loss) associated with the connection between circuits as low as possible due to the nature of the frequency to be handled. However, when trying to apply a BGA mounting that is simple and easy to handle, it is difficult to apply the BGA mounting as it is because of the above-mentioned problems. An object of the present invention is to provide a high-frequency circuit module that can be mounted on a circuit board with high accuracy by a BGA and a mounting structure of the high-frequency circuit module.

  The high frequency circuit module of the present invention includes a dielectric substrate having a BGA formed on a waveguide terminal and a plurality of electrode pads. And BGA is comprised with a solder ball and the composite solder ball which has a core part which is hard to deform | transform with the dead weight of the said high frequency circuit module at the time of reflow mounting, and the solder layer which coat | covers the core part.

  With this configuration, the high-frequency circuit module is supported by a composite solder ball having a core portion that is not easily deformed even if the solder melts during reflow mounting. For this reason, sinking of the solder ball does not occur, and the standoff can be accurately controlled.

  The mounting structure of the high-frequency circuit module according to the present invention corresponds to the high-frequency circuit module of the dielectric substrate having the BGA formed on the waveguide terminal and the plurality of electrode pads, and the electrode pad of the high-frequency circuit module through the BGA. The circuit board having the corresponding electrode pads connected to each other and the high-frequency circuit module and the circuit board are in contact with at least one of the high-frequency circuit module and the circuit board at a plurality of locations of the high-frequency circuit module and the circuit board. And a portion for ensuring a constant distance between the two.

  With the above configuration, the high-frequency circuit module can be accurately mounted on the circuit board with an inexpensive configuration while using the BGA.

(Points in the best mode of the present invention)
The high-frequency circuit module according to the present invention is a dielectric substrate in which ceramic materials such as HTCC (high temperature co-fired ceramics) and LTCC (low temperature co-fired ceramics) are laminated and fired to form multilayers, or Teflon (registered trademark) and BT resin. For example, it is formed on a dielectric substrate which is formed by laminating organic materials with relatively little loss in a high frequency region. This dielectric substrate is provided with the BGA structure described above. In the case where the BGA structure high-frequency circuit module is surface-mounted by solder reflow on a ceramic or resin circuit board, the following problems are solved by using the following configuration.

  (1) In order to solve the problem that the solder ball is deformed by the weight of the high-frequency circuit module at the time of mounting, a structure in which the ball is not greatly deformed by the weight of the module even in a heating environment at the time of reflow may be used. The non-deformable structure is a solder layer having a surface layer of 10 to 50 μm that contributes to bonding, but the core portion contained therein is not deformed by the thermal environment received by the high-frequency circuit module in a mounting process such as reflow, A ball containing a non-solder material. Here, the non-solder material is, for example, a composite solder ball or a metal ball such as copper, nickel, or silver. When such a ball is used, the ball does not deform due to the weight of the high-frequency circuit module even when the solder is melted in the reflow process, so that the standoff during mounting, that is, the height between the bottom surface of the high-frequency circuit module and the circuit board is kept constant. It is.

  As described above, a part of the BGA is a normal solder ball, and the other part is a ball that is not deformed by a thermal environment, for example, a solder-coated composite solder ball. Here, in a predetermined case, the outer shapes of the two types of balls are the same size. The reason why the two-ball configuration is adopted is that a ball that does not deform due to a thermal environment is expensive. From this point of view, it is desirable that the number of balls that are not deformed by the thermal environment is at least three, usually four or more, per high-frequency circuit module.

  According to this structure, when solder is melted in the reflow mounting process, all of the general solder balls are melted. However, in the case of a ball that is not deformed by the thermal environment, only the 10-50 μm solder on the surface layer melts, contributing to the joining. To do. Since the core portion is supported without melting, the high frequency circuit module does not tilt or sink. That is, there is a feature that deformation does not occur at the time of reflow mounting and an accurate standoff can be secured, which is very effective for connection between waveguides.

  According to this structure, the high-frequency circuit module and other electronic components can be mounted on the circuit board at the same time, and even a high-frequency circuit module that is more sensitive to the finished shape than general electronic components must be specially adjusted. It is possible to implement batch reflow without using it. As a result, surface mounting that solves the problems found in the prior art can be performed, so that stable characteristics can always be obtained without impairing variations in characteristics and transmission loss that occur during mounting.

  On the other hand, there is the following structure as a modified example of the above-described mounting configuration (the third embodiment described later). First, it is a structure in which all of the ball portions surrounding the waveguide terminal are composed of balls that are not deformed by the thermal environment. This is an effective means in a circuit in which the phase difference of signals handled by the high-frequency circuit module becomes a problem. When the frequency handled by the high-frequency circuit module increases and the frequency in the millimeter wave region is handled, for example, when the phase difference of signals handled between multiple waveguide terminals becomes a problem, such as a multi-element antenna, If the circuit module is inclined, the phase between signals may change.

  In such a case, it is necessary to make all the heights of the ball portions surrounding the waveguide terminal uniform. However, it is extremely difficult to achieve this with a normal solder ball because of the solder deformation described above. Therefore, all the ball array portions surrounding the waveguide terminals are formed of balls that are not deformed by the thermal environment. As a result, both electrical conduction between the high-frequency circuit module and the circuit board and high-precision control of the stand-off can be satisfied, and the stand-off after mounting is accurately maintained while having a function of blocking electromagnetic wave leakage. Will be able to.

  As another modification, there is a configuration in which all of the ball array portion surrounding the waveguide terminal is composed of solder balls, and the balls that are not deformed by the thermal environment are discretely arranged only in the periphery thereof (implementation to be described later) Forms 2 and 4). This is an effective structure when the high-frequency circuit module is downsized and the waveguide terminals are installed adjacent to each other. All the balls surrounding the waveguide terminal that is responsible for the electromagnetic shielding effect are formed of solder balls that deform at the reflow temperature, and the balls that do not deform due to the thermal environment that is responsible for controlling the sinking of the high-frequency circuit module are placed around the balls. Use. At this time, the ball that is not deformed by the thermal environment has a smaller outer diameter than the solder ball (Embodiment 4). By reducing the diameter of the ball that does not deform in the thermal environment, it is possible to stably realize a structure superior in shielding performance to any structure described so far. The principle will be described below.

  The distance d between the solder balls surrounding the waveguide terminal is set to λ / 4 or less (λ is the wavelength) of the wavelength determined from the frequency used in the high-frequency circuit. Thus, the same effect can be obtained without providing a continuous shield structure. However, the smaller the physical gap, the more electromagnetically advantageous. That is, it is advantageous in terms of electrical characteristics that the distance between the solder balls is as narrow as possible. For this reason, the gap between the solder balls is desired to be mounted as narrow as possible, but the risk of solder bridges increases. There is the following structure that can cope with this increased risk and can control the deformation amount of the solder ball.

  The principle that the high-frequency circuit module is supported by the ball that is not deformed by the thermal environment when the solder ball melts in the reflow process and the high-frequency circuit module sinks to a certain distance as described above. In the above-described structure, it was assumed that the outer diameter of the solder ball and the ball that is not deformed by the thermal environment are the same. However, in the other modifications described above, the outer diameter of the ball that is not deformed by the thermal environment is set smaller than that of the solder ball. Thereby, the sinking amount of the solder ball at the time of reflow increases. That is, the melted solder becomes a flat sphere having an elliptical cross section, but the ball that does not deform due to the thermal environment is supported and does not sink further, so that no defect due to the bridge occurs. For this reason, the interval between adjacent solder balls can be set narrower than usual.

  This structure also has the feature that the stand-off can be finely controlled just by changing the outer diameter of the small-diameter ball without changing the pitch of the ball adsorption jig of the ball mounting machine when making the BGA. There is also an advantage of easy adjustment. In this way, by setting the outer diameter of the ball that does not deform due to the thermal environment to be smaller than that of the solder ball, the gap between the solder balls around the waveguide terminal where a strong shield is required can be kept as narrow as possible, and the shielding characteristics are improved. To do.

  To deal with the problem (2), the problem that BGA mounting makes it difficult to inspect the connection after mounting, bring the part that would cause a problem when solder ball mounting defects occur to a position where it can be directly inspected. That's fine. In other words, the signal terminals, control signal terminals, signal ground terminals and bias terminals, which are terminals that need to be managed in connection, are all arranged only on the outermost ball row so that all pins can be observed directly. To do. And all the balls outside the outermost circumference that do not cause a big problem even if some connection failure or bridge occurs are all ground terminals or non-circuit connection terminals (not electrically connected, only mechanical connection is performed. The above problem can be solved. From the viewpoint of electrical characteristics of the high-frequency circuit module, in order to suppress electromagnetic noise, it is desirable that the ball inside the outermost periphery be a grounded non-circuit connection terminal rather than a floating non-circuit connection terminal.

  After the terminal arrangement with respect to the BGA, the outermost balls are inspected visually or optically after the mounting is completed to eliminate the above-mentioned defects. At this time, if an optical inspection device combining a TV camera with a prism or mirror and an image processing technique are introduced, automatic inspection is also possible.

  In the method described above, short (bridge connection), open (gap formation), and snowball failure (incomplete joint) that occur between the inner balls other than the outermost circumference cannot be inspected. There is no need to carry out this inspection, so no problem will arise even if it is not carried out. The reason will be described with reference to the drawings in the first embodiment.

(Embodiment 1) -Example using composite solder balls for standoff control-
FIG. 1 is a sectional view showing a high-frequency circuit module according to Embodiment 1 of the present invention. However, the solder resist and the overcoat glass are not shown in FIG. 1, and the number of solder balls is omitted. FIG. 2 is a view of the high-frequency circuit module shown in FIG. 1 as viewed from the bottom side. 3 is a cross-sectional view taken along line III-III in FIG. FIG. 4 is a cross-sectional view of the state in which the high-frequency circuit module is mounted on the circuit board. FIG. 5 is a cross-sectional view taken along line VV in FIG. 2 in a state where the circuit board is mounted on the circuit board. 6 is a cross-sectional view taken along the line VI-VI in FIG. 2 in a state of being mounted on a circuit board, and corresponds to FIG.

  In FIG. 1, an LTCC substrate (low-temperature fired ceramic substrate) that can be easily multilayered is used for the ceramic substrate 1 of the high-frequency circuit module 10. The surface shape of the ceramic substrate 1 is 18 mm × 20 mm, and the thickness is 1 mm. The ceramic substrate 1 is provided with a cavity 37 in which a high-frequency semiconductor element 31 is fixedly housed. The LTCC substrate 1 contains wiring as an electric circuit and a microstrip line-waveguide converter (not shown). The upper surface of the ceramic substrate 1 is fixed with a high melting point solder 23 such as gold tin, and a cap 35 formed by pressing a Kovar flat plate is hermetically sealed so that moisture or the like does not enter the inside. Solder balls 3 formed on the waveguide terminal 7 and the pad electrode 5 of the ceramic substrate are disposed on the bottom surface of the ceramic substrate 1.

  In FIG. 2, solder ball mounting pads (ceramic substrate pad electrodes) having an opening diameter of 0.5 mm are arranged on the back surface of the ceramic substrate 1 at a pitch of 1 mm, on which a commercially available lead-free pad having an outer diameter of 0.6 mm is arranged. Solder balls (Senju Metal Sn-3Ag-0.5Cu, Eco Solder Ball S) are regularly mounted. However, no ball is mounted in the central area Ao due to cost or reasons described later.

  A signal terminal, a control signal terminal, a signal ground terminal, and a bias terminal are arranged on the outermost ball array (outside the area A) (the distinction between these terminals is not shown). The solder ball on the inner periphery shown in the area A excluding the outermost periphery is provided with a normal ground terminal and a ground terminal as an electromagnetic shield that blocks leakage of electromagnetic waves surrounding the waveguide terminal. All the balls on the inner circumference are ground terminals.

  Of the outermost ball row, the balls at the four corners are not the solder balls but the composite solder balls 3a in which the resin core 15 that is not deformed even at the solder reflow temperature is coated with solder. FIG. 3 is a cross-sectional view of a portion where the composite solder ball 3a is disposed. In FIG. 3, the composite solder ball 3a is a commercially available product (Micropearl SOL manufactured by Sekisui Chemical Co., Ltd.) and has a resin core 15 made of a material that does not deform at the soldering reflow temperature. A lead-free solder coat 13 having a thickness of approximately 30 μm is applied to the surface of the composite solder ball 3a having an outer diameter of 0.6 mm. The composite solder ball 3a and the solder ball 3b are connected to the ceramic substrate pad electrode 5 by a method described later. An overcoat glass 4 is disposed between the ceramic substrate pad electrodes 5 to ensure insulation.

  Next, a method for manufacturing the high-frequency circuit module of the present embodiment will be described. First, a high-frequency circuit module in which the solder balls are removed from the high-frequency circuit module shown in FIG. 1 is assembled (details of assembly are omitted). Next, solder flux is supplied to the pad electrode on the back surface of the ceramic substrate of the high-frequency circuit module on which no solder ball is mounted. The method was performed by a printing method using a 100 μm thick stencil having the same opening diameter as the pad electrode of the ceramic substrate.

  Next, in a ball bonder (ball mounting machine), the lead-free solder balls 3b are collectively sucked by a vacuum suction nozzle and are collectively mounted on a ceramic substrate. Since the previously supplied flux has an appropriate viscosity, the solder ball 3b can be easily attached to the pad portion and does not move. However, at this time, solder balls are not mounted on the four corner portions of the ceramic substrate 1 shown in FIG. Next, the composite solder balls 3a having the same outer diameter as the solder balls 3b are mounted on the pad electrodes at the four corners of the ceramic substrate. For mounting, a single suction nozzle / ball mounting machine (a device for sucking and mounting solder balls one by one) is used.

  The above method is used because it is structurally difficult to incorporate a mechanism for distinguishing and mounting the solder ball 3b and the composite solder ball 3a into the ball mounting machine in order to simultaneously mount the solder ball 3b and the composite solder ball 3a. Therefore, a two-stage method is applied in which the process of mounting the solder balls 3b is performed first, and then the process of mounting the composite solder balls 3a one by one. As a result, even in a BGA structure in which the solder balls 3b and the composite solder balls 3a are mixed, it is possible to mount a desired ball at a predetermined position without confusing both.

  The high-frequency circuit module after mounting the solder balls performs melting and fixing of the solder by passing through a nitrogen reflow furnace. The reflow conditions were an oxygen concentration of 100 ppm, a peak temperature of 235 ° C., and a temperature profile of 200 ° C. or higher with a temperature profile of about 100 seconds. The time from charging to unloading to the reflow furnace is about 5 minutes. After the reflow process, the high-frequency circuit module is visually inspected for defects such as chipping, deformation, bridges, etc., on the back ball. Through the above method, the high-frequency circuit module of the present embodiment is completed.

  Next, the completed high frequency circuit module is reflow mounted on the circuit board. FIG. 4 is a cross-sectional view showing a state where the high-frequency circuit module is mounted on the circuit board. FIG. 4 also shows an optical inspection apparatus for inspecting the connection state of the solder balls in the mounting structure. In FIG. 4, circuit board pad electrodes (corresponding electrode pads) 55 and waveguides 57 corresponding to the ball array on the back surface of the ceramic substrate 1 of the high-frequency circuit module 10 are formed on the circuit board 51. The back surface of the ceramic substrate 1 and the mounting surface of the circuit substrate 51 are connected by a solder material through a solder layer of a solder ball 3 including composite solder balls.

  The circuit board 51 used is a commercially available BT resin board (manufactured by Mitsubishi Gas Chemical), and the opening diameter of the circuit board pad is 0.5 mm. First, a lead-free solder paste is supplied onto the pad electrode 51 on the mounting surface of the circuit board. The method was performed by a printing method using a stencil having the same opening diameter as the pad electrode of the circuit board and a thickness of 100 μm.

  Next, the high frequency circuit module 10 was vacuum-sucked and mounted on the circuit board 51. Mounting was carried out using a mounter (mounting device) with an image monitor. In the high-frequency circuit module 10, the previously supplied solder paste has an appropriate viscosity, and therefore does not fall off the circuit board pad portion 55.

  After mounting the high-frequency circuit module 10 on the circuit board 51, surface mounting was performed using a nitrogen reflow furnace. The reflow conditions are the same as those described above. The time from loading to unloading to the reflow furnace is the same.

  FIG. 5 is a cross-sectional view of a portion where the solder balls 3b are arranged in a state where the high-frequency circuit module is mounted on the circuit board as described above. FIG. 6 is a cross-sectional view including the composite solder ball 3a in the same state. The distance between the circuit board 51 and the ceramic substrate 1 is determined by the size of the resin core 15. That is, at a plurality of locations, the resin core 15 determines the distance between the two, and ensures a constant distance between the two.

  The completed mounting board shown in FIG. 4 is observed by the optical inspection device 70 only for the outermost peripheral ball that can be visually observed. The optical inspection device 70 includes a camera 71, a lens 72, and a prism 73. Problems with solder connection that occur in the BGA mounting process by inspection using the optical inspection device 70, such as circuit module tilt, short (solder bridge), open (gap formation), snowman failure (incomplete joint), etc. Check if there is any. Thus, the mounting of the high-frequency circuit module in the present embodiment on the circuit board is completed.

  According to the present embodiment, the stand-off control is performed by making the ball at the corner of the BGA of the high-frequency circuit module 10 into a composite solder ball. As a result, the composite ball that does not melt greatly even if the solder melts during reflow mounting supports the high-frequency circuit module, so that the solder ball does not sink. This was confirmed by the following evaluation method.

  The circuit board 51 on which the completed high-frequency circuit module 10 is mounted is embedded in a resin, and after the resin is cured, the BGA section is subjected to cross-sectional polishing, and the standoff is measured with a reading microscope. As a result of the inspection, it was confirmed that all the solder balls had a standoff of about 0.6 mm close to the outer shape of the composite solder ball. Here, the reason why the standoff is not exactly 0.6 mm is that, as described above, the composite solder ball 3a is composed of the resin core 15 and the solder coat 13 for connecting the surface thereof. This is because the coating 13 sinks and the ceramic substrate 1 and the circuit board 51 made of resin have slight warpage and undulation.

  Regarding the mechanical strength, as can be seen from FIG. 2, since there are a large number of ground terminals, even if some of them are missing, the overall mechanical strength, that is, the joint strength of the entire high-frequency circuit module is hardly affected. Next, regarding an electrical circuit problem, if a large number of ground terminals are concentrated in a general electrical circuit, even if several of them are missing or a short circuit occurs, it does not cause a circuit problem. The same can be said for this high-frequency circuit module.

  In short, when a non-connected portion occurs in the ball surrounding the waveguide terminal 7, that is, when an open defect or a snowman defect occurs, high-frequency electromagnetic coupling between the waveguide terminals increases, and insulation between the terminals occurs. The problem that the property is lowered, that is, the problem that the shield characteristic called isolation is lowered occurs.

  Even if the number of ball rows is two from the viewpoint of design, the same concept holds. Furthermore, even when the solder ball rows between the waveguide terminals, which are considered to be the most dangerous, are not connected, there are unconnected solder balls between the waveguide terminals, which are on the ceramic substrate side. Or since both are grounded on the printed circuit board side, the shielding effect does not deteriorate so much. The same is true for snowmen. In addition, even if a short circuit failure occurs in this part, there is no problem because it goes to the safety side rather than the shield function.

  As described above, since all the balls in the region A are ground terminals, even if a slight connection failure or a short-circuit failure due to a bridge occurs, it does not become a big problem. That is, since these are terminal groups that do not need to manage the connection state at all, there is no need to perform inspection.

  The high-frequency circuit module and the mounting structure thereof according to the present embodiment satisfy both the solution of the problem associated with deformation and sinking of the solder ball, which has been a problem of BGA mounting, and the ease of BGA connection inspection. It became possible to provide.

(Embodiment 2) -Example in which composite solder balls are arranged on the inner circumference instead of the outermost circumference-
Next, an example of the high-frequency circuit module according to Embodiment 2 of the present invention will be described. The basic configuration of the high-frequency circuit module in the present embodiment is the same as the example in the first embodiment. The material of each constituent member is the same as in the first embodiment. In the following, the difference between the high frequency circuit module of the present embodiment and the first embodiment will be described.

  FIG. 7 is a plan view of the back surface of the high-frequency circuit module according to Embodiment 2 of the present invention. In FIG. 7, the composite solder balls 3a are arranged at the four innermost corners (four corners of the central area Ao) different from the first embodiment. When the composite solder ball 3a is arranged at such a site, the following effects can be expected.

  The ceramic substrate 1, which is a component of the high-frequency circuit module 10, and the circuit board 51 on which the high-frequency circuit module 10 is mounted differ from metal materials because the material is ceramic or resin. May be warped or deformed. If this is ignored, depending on the conditions, the distance between the ceramic substrate 1 and the circuit substrate 51 after mounting (inter-substrate distance) increases or decreases, and electrical continuity is obtained in a wide range between the ceramic substrate and the circuit substrate. May occur (open state), or a short circuit may occur.

  As described in the first embodiment, when such a defect occurs locally, no problem occurs, but it is not preferable that it occurs over a wide range. In the arrangement of the first embodiment, it is the central area Ao of the ceramic substrate 1 that is most susceptible to this influence. For this reason, the influence is mitigated by performing a neutral arrangement in which no balls are arranged in the central area Ao. . However, when the range of influence spreads and a continuous open state (a state where the ball connection of the gap formation is continuous) occurs in the ball surrounding the waveguide terminal 7, it is derived from the frequency used in the above-described high-frequency circuit. It becomes impossible to maintain the gap d between balls having a wavelength of λ / 4 or less. As a result, the function of continuously shielding the periphery of the waveguide terminal 7 is lost, and the purpose of blocking leakage of electromagnetic waves is lost.

  In order to avoid this, as shown in FIG. 7, the composite solder balls 3 a are arranged at the four corners of the central area Ao inside the area A. As a result, it is possible to provide a module that can be mounted with the distance between the substrates kept constant as much as possible even with the use of a ceramic substrate or a circuit substrate having deformation such as warping or twisting and with little change in standoff.

(Embodiment 3) -Example where all balls surrounding waveguide terminals are composite solder balls-
Next, a third embodiment of the present invention will be described. The basic configuration of the high-frequency circuit module of the present embodiment is the same as that of the first embodiment. The material of each constituent member is the same as in the first embodiment. Hereinafter, the high-frequency circuit module according to the present embodiment will be described with respect to differences from the first embodiment.

  FIG. 8 is a plan view of the back surface of the high-frequency circuit module according to Embodiment 3 of the present invention. Unlike the first embodiment, the composite solder balls 3 a are arranged on all the balls surrounding the waveguide terminal 7. FIG. 9 is a cross-sectional view of the composite solder ball mounting portion. When the composite solder ball is arranged at such a portion, the following effects can be expected.

  The object of the present embodiment is to form a high frequency in which the phase difference between the waveguide terminals becomes a problem by configuring all the solder balls surrounding and adjacent to the waveguide terminals 7 with the composite solder balls 3a. The present invention is advantageously applied to circuit modules, for example, circuits that handle phase differences of electrical signals, such as phased array antenna transmission and reception modules. That is, a high-accuracy standoff can be ensured by configuring the ball surrounding the waveguide terminal only with the composite solder ball 3a. According to the present embodiment, it is possible to provide a high-reliability high-frequency circuit module that effectively solves the problem of phase difference between waveguide terminals.

  In FIG. 8, all the balls surrounding the waveguide terminal 7 among the pad electrodes of the ceramic substrate are composite solder balls and are ground terminals. When the composite solder balls 3a are arranged in this way, the distance between the ceramic substrate 1 and the circuit board 51 is determined by the connecting portion by the composite solder balls 3a, and it is possible to provide a high-frequency circuit module mounting structure with high accuracy. It becomes.

  In the above description, the structure in which all the balls surrounding the waveguide terminal 7 are composite solder balls has been described. However, if high precision is not required for the standoff after mounting, a part of the ball surrounding the waveguide terminal 7 may be used as the solder ball 3b. The reason is that the composite solder balls are expensive and take time to mount.

(Embodiment 4) -Example using small-diameter composite solder balls-
Next, an example of Embodiment 4 of the present invention will be described. The basic configuration of the high-frequency circuit module 10 of the present embodiment is the same as that of the first embodiment. The material of each constituent member is the same as in the first embodiment. Hereinafter, the high-frequency circuit module according to the present embodiment will be described with respect to differences from the first embodiment.

  FIG. 10 is a plan view of the back surface of the high-frequency circuit module according to Embodiment 4 of the present invention. FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. Unlike the first embodiment, the composite solder ball 3s in the present embodiment has a smaller outer diameter than the solder ball 3b. As already described, the distance d between the balls surrounding the waveguide terminal 7 must satisfy the condition of λ / 4 or less. However, in order to obtain a high shielding function, it is advantageous that the gap distance d is as short as possible. For this reason, it is desired to use the solder balls side by side at the smallest possible pitch, but there is a risk of solder bridges (short circuit).

  Therefore, by setting the composite solder ball 3s to be smaller than the solder ball 3b and increasing the deformation of the solder ball around the waveguide terminal 7 that needs to be shielded, the gap between the balls is narrowed, and the shielding characteristics are improved. Improve. By selecting the optimum value of the dimensions of the composite solder ball 3s, stable production can be achieved without causing a bridge.

  The outer diameter of the solder ball 3b used in the fourth embodiment is the same 0.6 mm as in the first embodiment. The outer diameter of the composite solder ball 3s is 0.5 mm, which is slightly smaller than the solder ball 3b. The composite solder ball 3s is composed of a resin core 15s and a lead-free solder coat 13s applied to the surface of the resin core 15s. The lead-free solder coat 13s is the same as that of the first embodiment and has a thickness of about 30 μm.

  It should be noted here that the small-diameter ball 3s is always in contact with the solder paste at the time after the high-frequency circuit module 10 is mounted on the circuit board 51 and before reflow mounting. Otherwise, solder unconnection (gap formation) occurs.

  In the present embodiment, as in the first embodiment, lead-free solder paste is supplied onto the pad electrode on the mounting surface of the circuit board, but the stencil at that time is 0.4 mm which is slightly smaller than the pad electrode on the circuit board. A slightly thicker one having an opening diameter and a thickness of 150 μm was used. This is an adjustment for reducing the influence of using balls having different outer shapes, and is an operation for increasing the height without changing the volume of the solder paste supplied onto the pad. When the high-frequency circuit module is mounted on the circuit board supplied with the solder paste in this way, reflow can be performed with the solder paste sufficiently in contact with the small-diameter composite solder balls 3s. As a result of the reflow, it was confirmed that the solder wets all the balls and the solder balls having the expected shape are formed.

  When BGA mounting is performed, if a small diameter ball is used for a part, it is easy to be affected by warping and twisting of the substrate. Therefore, it is desirable to use a substrate that is as flat as possible. A small-diameter composite solder ball 3s is also arranged around the periphery to minimize this effect. The completed module was inspected in the same manner as in the first embodiment, but no abnormality was detected.

  As described above, the embodiment has been described, but the method of using a composite solder ball as a ball that is not deformed by a thermal environment has been described. However, if this purpose can be achieved, a solder coat is not necessarily applied to the resin core. It is not necessary to have a composite solder ball. High temperature solder or metal balls that do not melt even at the reflow temperature of the solder may be used for the core.

  In the mounting structure of the high-frequency circuit module of the present invention, the high-frequency circuit module is located between the high-frequency circuit module and the circuit board, and in contact with at least one of the high-frequency circuit module and the circuit board at a plurality of locations of the high-frequency circuit module and the circuit board. And a portion for ensuring a constant interval. In the above-described embodiment, the portion that keeps the distance between them constant has been described for the resin core of the composite solder ball, but is not limited thereto.

  For example, the high-frequency circuit module and the circuit board may be provided with a plurality of protruding portions protruding from one side to the other side, and a portion that keeps the distance between them constant may be the protruding portion. The protrusion may be, for example, a metal protrusion structure on a circuit board, a metal lead or a metal pin on the high frequency circuit module side. In short, it is only necessary to obtain a function of electrically connecting the substrates and a standoff of a required part.

  With the above configuration, the high-frequency circuit module can be accurately mounted on the circuit board with an inexpensive configuration while using the BGA.

  Further, the connection may be implemented using a conductive adhesive or the like instead of solder, and may be properly used depending on the situation in order to obtain an expected result. The printed board used for the circuit board may be a general FR-4 board, a ceramic board, a Teflon (registered trademark) board, a liquid crystal polymer board, or a flexible board using a polyimide board.

  As described above, the composite solder ball can be disposed so as to surround the waveguide terminal along the edge of the waveguide terminal of the high-frequency circuit module. With this configuration, a more accurate standoff can be ensured, so that it can be applied to a high-frequency circuit module in which a phase difference between waveguide terminals becomes a problem, that is, a circuit that handles a phase difference of an electric signal.

  Moreover, the outer diameter of the composite solder ball can be made smaller than the outer diameter of the solder ball. With this configuration, the gap between the solder balls can be narrowed and the shield characteristics can be improved. In addition, by selecting the optimum value of the dimensions of the resin balls, stable production can be achieved without generating a bridge.

  Further, when the BGA is viewed in plan, the inner electrode pads other than the outermost periphery may be configured such that none of the signal terminals, the control signal terminals, the signal ground terminals, and the bias terminals are arranged. With this configuration, after the mounting is completed, only the outermost peripheral ball can be visually or optically inspected to reliably inspect the solder joint failure of the high-frequency circuit module.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The high-frequency circuit module and the mounting structure of the high-frequency circuit module according to the present invention make it possible to connect a high-frequency circuit module having a waveguide terminal to a circuit board with high accuracy by BGA, and thus make a great contribution in this field. It is expected.

It is sectional drawing of the high frequency circuit module in Embodiment 1 of this invention. It is a reverse view of the high frequency circuit module of FIG. It is sectional drawing which follows the III-III line of FIG. It is sectional drawing of the state which mounted the high frequency circuit module of FIG. 1 on the circuit board. It is sectional drawing of the connection part of the mounted state (position corresponding to the VV line of FIG. 2). It is sectional drawing of the connection part of the mounted state (position corresponding to the VI-VI line of FIG. 2). It is a reverse view of the high frequency circuit module in Embodiment 2 of this invention. It is a reverse view of the high frequency circuit module in Embodiment 3 of this invention. It is sectional drawing which follows the IX-IX line of FIG. It is a reverse view of the high frequency circuit module in Embodiment 4 of this invention. It is sectional drawing which follows the XI-XI line of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Ceramic substrate, 3 Solder ball, 3a Composite solder ball, 3b Solder ball, 3s Small diameter composite solder ball, 4 Overcoat glass, 5 Ceramic substrate pad electrode, 7 Waveguide terminal, 10 High frequency circuit module, 13 Solder coat, 13s small diameter ball solder coat, 15 resin core, 15s small diameter ball resin core, 23 high melting point solder, 31 high frequency semiconductor element, 35 cap, 37 cavity, 51 circuit board, 54 solder resist, 55 circuit board pad electrode, 57 Waveguide, 70 optical inspection device, 71 camera, 72 lens, 73 prism, Ao central region, A inner region.

Claims (8)

A high-frequency circuit module comprising a dielectric substrate having a BGA (Ball · Grid · Array) formed on a waveguide terminal and a plurality of electrode pads,
The high-frequency circuit module, wherein the BGA includes a solder ball and a composite solder ball having a core portion that is difficult to be deformed by its own weight during reflow mounting and a solder layer that covers the core portion.   The high frequency circuit module according to claim 1, wherein the composite solder ball is positioned so as to surround the waveguide terminal along an edge of the waveguide terminal of the high frequency circuit module.   The high frequency circuit module according to claim 1, wherein an outer diameter of the composite solder ball is smaller than an outer diameter of the solder ball.   Any of the signal pads, the control signal terminals, the signal ground terminals, and the bias terminals are not arranged on the electrode pads inside the outermost periphery when the BGA is viewed in a plan view. The high-frequency circuit module described.   A mounting structure of a high-frequency circuit module, wherein the high-frequency module according to any one of claims 1 to 4 and a circuit board are connected via the BGA. A dielectric substrate high-frequency circuit module having a BGA (Ball / Grid / Array) formed on a waveguide terminal and a plurality of electrode pads;
A circuit board having corresponding electrode pads connected to the electrode pads of the high-frequency circuit module through the BGA;
Located between the high-frequency circuit module and the circuit board, and in contact with at least one of the high-frequency circuit module and the circuit board at a plurality of locations of the high-frequency circuit module and the circuit board, a constant interval between them is ensured. And a mounting structure for a high-frequency circuit module.   The BGA includes a composite solder ball composed of a core portion and a solder coat that coats the core portion, and a portion that keeps a constant distance between the two is the core portion. 7. A mounting structure of the high-frequency circuit module according to 6.   The said high frequency circuit module and the said circuit board are equipped with the protrusion part which protrudes in the other side from any one in several places, The part which ensures the space | interval of both is a protrusion part. High frequency circuit module mounting structure.

Images