JP2004047774A - Method for manufacturing mounted substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a mounted substrate capable of preventing mounting-related defects due to voids inside the active resin adhesive in the manufacturing of a double-sided substrate wherein an active resin adhesive is used. <P>SOLUTION: In this method for manufacturing a mounted substrate wherein the first side and the second side of a substrate are mounted with electronic components, respectively, a soldering paste containing an active thermosetting resin having a thermosetting temperature T3 which is higher than a solder melting point T2 is applied, but only to the second side to be processed at a later stage. This active soldering paste is heated only in a second reflow for the second side, and this prevents mounting-related defects due to voids inside the active resin adhesive. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a mounting board for manufacturing a mounting board by mounting an electronic component on the board.
[0002]
[Prior art]
As a method for mounting electronic components such as semiconductor chips, a method using solder bonding is widely used. As a method of the solder joining, a method of applying a thermosetting resin adhesive material on electrodes of a substrate in advance before mounting components is adopted. In this method, the substrate is heated after the solder bumps of the electronic component have landed on the electrodes, so that the solder bonding between the solder bumps and the electrodes and the thermosetting of the resin adhesive are performed in the same heating step. According to this method, there is an advantage that it is not necessary to provide a reinforcing underfill resin forming step as an independent step.
[0003]
[Problems to be solved by the invention]
However, in the case where the electronic component mounting method using the resin adhesive is applied to a double-sided mounting board on which electronic components are mounted on both front and rear surfaces, the following inconvenience may occur. . As described above, in this mounting method, the solder bonding between the solder bumps and the electrodes and the thermosetting of the resin adhesive are performed in the same heating step. The electronic components on the surface are heated again in the second heating process for the second surface after the resin is heated in the first heating process for the first surface.
[0004]
At this time, if a void is formed in the resin adhesive of the electronic component on the first surface side by the gas generated from the substrate in the first heating step, a defect due to reheating of the void may occur. Easy to occur. For example, when the gas in the void is separated from the resin by expansion due to reheating, or when a void is generated in the vicinity of the joint, the solder in the joint melts at the time of reheating and flows into the void. As a result, poor conduction at the joint may occur. Then, such a defect may cause a decrease in mounting quality.
[0005]
Therefore, the present invention provides a method of manufacturing a mounting board that can prevent a mounting defect caused by a void inside the resin adhesive in manufacturing of a mounting board performed on a double-sided mounting board using a resin adhesive. The purpose is to provide.
[0006]
[Means for Solving the Problems]
The method for manufacturing a mounting board according to claim 1, wherein the mounting board has electronic components mounted on a first surface and a second surface behind the first surface, respectively. In the mounting step, a first paste supplying step of supplying a solder bonding paste not containing a thermosetting resin to the first surface to be mounted first, and mounting an electronic component on the first surface after the paste is supplied, and A first mounting step of landing the connection electrode of the component on the first electrode provided on the first surface; and heating the substrate after the first mounting step to solder the connection electrode to the first electrode. A first heating step, a second paste supply step of supplying the solder bonding paste containing the thermosetting resin to the second surface of the substrate on which the first surface has been mounted, and an electron supply to the second surface after the paste supply. After mounting the components, the connection electrodes for the electronic components are provided on the second surface. A second mounting step of landing on the second electrode, and heating the substrate after the second mounting step to melt the connection electrode or the bonding solder portion previously supplied to the second electrode, thereby connecting the connection electrode. And a second heating step of starting the thermosetting of the thermosetting resin by soldering to the second electrode.
[0007]
According to a second aspect of the present invention, there is provided the method of manufacturing a mounting board according to the first aspect, wherein the first heating step includes heating the substrate to a temperature equal to or higher than the heating temperature in the second heating step.
[0008]
4. The method of manufacturing a mounting board according to claim 3, wherein the mounting board has electronic components mounted on a first surface of the substrate and a second surface behind the first surface, respectively. In the mounting process, the second surface to be mounted later is set in advance as a second paste supply surface to which a solder bonding paste containing a thermosetting resin is supplied, and in the electronic component arrangement at the time of designing a board, the heat is applied to the second surface. Electronic components to which a mounting method using a curable resin is applied are preferentially arranged on the second surface.
[0009]
5. The method of manufacturing a mounting board according to claim 4, wherein the mounting board has electronic components mounted on a first surface of the substrate and a second surface behind the first surface. Compare the type and quantity of electronic components mounted on each side of the board, and mount the surface with the higher percentage of electronic components to which the mounting method using thermosetting resin can be applied later in the component mounting process Set as the target second surface.
[0010]
According to the present invention, a soldering paste containing a thermosetting resin as a kind is supplied only to the second surface to be mounted later, and the soldering paste is heated by the second heating for the second surface. By limiting the process to only one step, it is possible to prevent a mounting defect caused by a void inside the resin adhesive.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are process explanatory views of a method of manufacturing a mounting board according to one embodiment of the present invention, and FIG. 3 is a graph showing a temperature profile of a reflow process in the manufacturing method of the mounting board of one embodiment of the present invention. is there. In the present embodiment, a process for manufacturing a mounting substrate by mounting electronic components by soldering on a substrate having electrodes formed on both surfaces is shown.
[0012]
In FIG. 1A, reference numeral 1 denotes a substrate for double-sided mounting, and a first surface 1a (upper surface in FIG. 1) of the substrate 1 and a second surface 1b (lower surface in FIG. 1) behind the first surface include: An electrode 2 as a first electrode and an electrode 3 as a second electrode are respectively formed. The first surface 1a is a surface to be mounted first in a process of manufacturing a mounting substrate by mounting electronic components on both front and back surfaces of the substrate 1.
[0013]
As shown in FIG. 1A, a cream solder 4 serving as a solder bonding paste is supplied by printing onto an electrode 2 serving as a first electrode formed on a first surface 1a (first paste supply step). ). The cream solder 4 contains solder particles in a paste-like flux, and is a bonding material intended only for solder bonding. It does not contain resin.
[0014]
Next, as shown in FIG. 1B, on the first surface 1a after the cream solder is supplied, an electronic component 5 having terminals 5a as connection electrodes at both ends is mounted (first mounting step). As a result, the terminal 5a lands on the electrode 3 via the cream solder 4. Thereafter, the substrate 1 is sent to a reflow process for reflow of the second surface directed to the first surface 1a. Here, heating is performed according to a predetermined heating profile (first heating step).
[0015]
The heating profile in the first surface reflow will be described with reference to FIG. When heating is started, the substrate 1 is heated to a preheating temperature T1 lower than the solder melting point temperature T2, and is maintained at this temperature for a predetermined time. Then, after the preheating, the temperature further rises and exceeds the solder melting point temperature T2, so that the solder component in the cream solder 4 is melted, and the terminal 5a is soldered to the upper surface of the electrode 2 via the melted solder. The solder melting point temperature is 183 ° C. for Sn / Pb solder and 220 ° C. for Sn / Ag solder. In this solder bonding, the oxide film formed on the surface of the terminal 5a is removed by the flux component in the cream solder 4, so that good bonding is ensured.
[0016]
Thereafter, the heating temperature further rises and reaches a maximum heating temperature Ta set at a temperature lower than the heat-resistant temperature T4 (about 250 ° C.). After maintaining this temperature for a predetermined time, the temperature gradually decreases. Here, when the maximum heating temperature Ta is set higher than the maximum heating temperature Tb in the second surface reflow described later, the moisture and the organic gas contained in the substrate 1 are reduced as much as possible by the heating during the first surface reflow. It is preferable because it can be released from the surface. In this case, the maximum heating temperature Ta is about 230 ° C to 240 ° C. At the time of reflow on the first surface, there is a space through which gas passes on the lower surface of the electronic component 5, so that mounting defects due to voids inside the resin adhesive do not occur.
[0017]
Subsequent to the mounting on the first surface 1a, mounting on the second surface 1b is performed. That is, as shown in FIG. 2A, a resin adhesive 6 which is a solder bonding paste is supplied around the electrode 3 on the second surface 1b by the dispenser 7 so as to cover the electrode 3 (second paste). Supply step). The resin adhesive 6 has an adhesive function of sealing and reinforcing the lower surface of the electronic component by adding an active component having an oxide film removing ability to a base mainly composed of a thermosetting resin such as an epoxy resin. In addition to the above, it also has a function as a flux for removing the oxide film on the solder surface at the time of solder joining to improve the solder joining property. Since the resin adhesive 6 removes the oxide film on the surface of the solder bump by the contained active component, there is no need to separately apply a flux, and a cleaning step after reflow, which is required in the conventional method using the flux, is omitted. It has the advantage of being able to.
[0018]
Here, a material having a thermosetting temperature higher than the melting point of the solder used for mounting is used as the thermosetting temperature of the base. Note that the thermosetting temperature in this embodiment is a temperature determined by differential scanning calorimetry (DSC) used for measuring a curing reaction of a resin material. That is, the relationship between the amount of heat and the temperature obtained in the process of heating a 10 mg sample at a heating rate of 10 ° C./min is plotted with the ordinate representing the amount of heat and the abscissa representing the temperature. Is formed. Then, a tangent is drawn from the inflection point on the high temperature side slope of the chevron curve, and the temperature at which the tangent intersects the horizontal axis is determined as the thermosetting temperature.
[0019]
Next, as shown in FIG. 2C, an electronic component 8 having a solder bump 9 as a connection electrode provided on the lower surface is mounted on the second surface 1b after the resin adhesive is supplied (second mounting step). Thus, the solder bumps 9 land on the electrodes 3 via the resin adhesive 6. At this time, the lower surface of the electronic component 8 is almost completely filled with the resin adhesive 6. After that, the substrate 1 is sent to a reflow process for the second surface reflow for the second surface 1b. Here, heating is performed according to a predetermined heating profile (second heating step).
[0020]
The heating profile in the second surface reflow is substantially the same as that in the first surface reflow as shown in FIG. 3, and when the temperature rises and exceeds the solder melting point temperature T2, the solder bump 9 is melted and the molten solder is melted. The terminal 5a is soldered to the electrode 3 via the terminal 5a. Here, the solder bumps 9 serve as connection electrodes for connecting the electronic component 8 to the substrate 1 and also serve as bonding solder portions supplied to the connection electrodes. In this solder bonding, even when an oxide film is formed on the surface of the electrode 3 by the heating during the first reflow, the oxide film is removed by the active component in the resin adhesive material 6, and good solder bonding property is secured. Is done.
[0021]
Thereafter, the heating temperature further rises and reaches a maximum heating temperature Tb set to a temperature higher than the thermosetting temperature T3 and lower than the heat-resistant temperature T4. After maintaining this temperature for a predetermined time, the temperature gradually decreases. Here, the maximum heating temperature Tb is lower than the maximum heating temperature Ta in the first surface reflow as described above.
[0022]
The heating causes the thermosetting reaction of the resin adhesive 6 to proceed in parallel. However, the thermosetting temperature T3 of the resin adhesive 6 is higher than the solder melting point T2 of the solder bump 9, so that the solder bump 9 When the molten solder wets the surface of the electrode 2, the resin adhesive 6 is in a state in which thermosetting has not yet started. Therefore, the flow of the molten solder in the resin adhesive 6 is ensured, and the self-alignment between the solder bump 9 and the electrode 3 is not hindered.
[0023]
After the molten solder is joined to the electrode 3, the heating is continued and the temperature rises. Next, the temperature is raised to the maximum heating temperature Ta beyond the thermosetting temperature T3, and after this temperature is maintained for a predetermined time, the process proceeds to a temperature decreasing process. In this heating process, the thermosetting of the resin adhesive 6 proceeds rapidly during the time t during which the temperature is maintained at the thermosetting temperature T3 or higher. This completes the mounting of the electronic component 5 on the first surface 1a.
[0024]
In the second surface reflow, the organic components and moisture contained in the inside of the substrate 1 are mostly gasified by heating, and are mostly gasified from the surface because the substrate 1 is already heated at a high temperature by the first surface reflow as described above. Since these gases are released and these gases are confined in the resin adhesive 6, the generation of voids is small. Further, even when a void is generated, since the resin adhesive 6 is not heated to a higher temperature thereafter, a defect caused by reheating the void, for example, the gas in the void is Such as peeling of the resin due to expansion due to heating, and if the voids are formed near the joint, the solder at the joint melts at the time of reheating and flows into the voids. There is no occurrence.
[0025]
The manufacturing method of the mounting substrate described in the above embodiment is applied in two modes as follows in production. The first aspect is that, in a design stage of a mounting board on which electronic components are mounted on both surfaces, the first surface of the electronic component is considered in consideration of whether or not the resin adhesive 4 is applied to the electronic component to be mounted. , To determine the distribution to the second surface.
[0026]
That is, when designing a mounting board for manufacturing a mounting board in which electronic components are mounted on the first surface of the substrate and the second surface on the back side of the first surface, respectively, a second mounting target to be mounted later in the component mounting process. The surface is set in advance as a second paste supply surface to which the solder bonding paste including the resin adhesive 6 is supplied. Then, in arranging the electronic components when designing the board, the electronic components to which the mounting method using the thermosetting resin is applied are preferentially arranged on the second surface. By arranging the electronic components according to such a policy when designing the board, the electronic components using the resin adhesive 6 are intensively arranged on the second surface to be mounted later. Therefore, a situation in which the used resin adhesive 6 goes through two thermosetting processes does not occur.
[0027]
On the other hand, a substrate that has not been taken into consideration as described above in the substrate design process is handled as follows. First, when the layout of electronic components on a double-sided board is presented, the types and quantities of electronic components mounted on each of the front and back surfaces of the board are compared. Then, the surface on which the proportion of electronic components to which the mounting method using the resin adhesive 6 can be applied is larger is set as the second surface to be mounted later in the component mounting process. The mounting method using the material 6 is applied.
[0028]
A mounting method that does not use the resin adhesive 6 such as a mounting method using cream solder is applied to the other electronic components on the second surface and the electronic components on the first surface. Thus, the electronic component using the resin adhesive 6 is arranged only on the second surface to be mounted later, and therefore, the situation in which the used resin adhesive 6 undergoes two thermosetting processes does not occur.
[0029]
【The invention's effect】
According to the present invention, a solder bonding paste having a function of removing the oxide film of the solder only on the second surface to be mounted later and containing a thermosetting resin as a kind is supplied. Since the heating is limited to one time in the second heating step for the second surface, it is possible to prevent a mounting failure caused by a void inside the resin adhesive.
[Brief description of the drawings]
FIG. 1 is a process explanatory view of a method for manufacturing a mounting board according to an embodiment of the present invention; FIG. 2 is a process explanatory view of a method for manufacturing a mounting board according to an embodiment of the present invention; FIG. Graph showing a temperature profile of a reflow process in a method of manufacturing a mounting board according to an embodiment [Description of reference numerals]
REFERENCE SIGNS LIST 1 board 1a first surface 1b second surface 2, 3 electrode 4 cream solder 5 electronic component 5a terminal 6 resin adhesive 8 electronic component 9 solder bump

Claims (4)

What is claimed is: 1. A method of manufacturing a mounting board, wherein electronic parts are mounted on a first surface of a substrate and a second surface on a back side of the first surface, respectively, wherein the first surface to be mounted first in a component mounting process is provided. A first paste supply step of supplying a solder bonding paste not containing a thermosetting resin, an electronic component mounted on the first surface after the paste is supplied, and a connection electrode of the electronic component provided on the first surface. A first mounting step of landing on the first electrode, a first heating step of heating the substrate after the first mounting step, and soldering the connection electrode to the first electrode, and mounting the first surface. A second paste supply step of supplying a solder bonding paste containing the thermosetting resin to the second surface of the completed substrate, and mounting an electronic component on the second surface after the paste is supplied to form a connection electrode of the electronic component. A second mounting step of landing on a second electrode provided on the second surface Heating the substrate after the second mounting step to melt the connection electrode or a bonding solder portion previously supplied to the second electrode, thereby soldering the connection electrode to the second electrode and performing the thermosetting. And a second heating step of starting thermosetting of the conductive resin. The method according to claim 1, wherein in the first heating step, the substrate is heated to a temperature equal to or higher than the heating temperature in the second heating step. A method of manufacturing a mounting board in which electronic components are mounted on a first surface of a substrate and a second surface behind the first surface, respectively, wherein a second surface to be mounted later is mounted in a component mounting process. A mounting method using the thermosetting resin is applied in advance to a second paste supply surface to which a solder bonding paste including a thermosetting resin is supplied, and to arrange electronic components at the time of designing a board. A method for manufacturing a mounting board, wherein electronic components are preferentially arranged on a second surface. What is claimed is: 1. A method of manufacturing a mounting board, comprising manufacturing a mounting board having electronic components mounted on a first surface of a substrate and a second surface on a back side of the first surface, wherein the electronic components are mounted on front and rear surfaces of the substrate, respectively. By comparing the type and quantity of the electronic component, the surface having the larger proportion of electronic components to which the mounting method using the thermosetting resin can be applied is set as the second surface to be mounted later in the component mounting process. Manufacturing method of the mounting substrate.

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