JPH06350237A - Land shape for solder precoating - Google Patents

Abstract

PURPOSE:To allow highly accurate positioning by forming a protrusion for a predetermined quantity of solder on a row of lands at at least one end thereof thereby preventing a component from shifting at the time of mounting CONSTITUTION:The land shape 2 for solder precoating is formed over the entire length of the row of lands such that a protrusion 4 is disposed adjacent to the the lead of an electronic component 7, at the tip 1 thereof, mounted on a the surface of a board through a solder while regulating the position of thereof on the plane. The protrusion 4 requires such quantity of solder as having effect on the positional regulation of the tip 1 of lead on the plane. Consequently, the length and width of land are 2.0mm and 0.16mm, respectively, and the width is widened to 0.20mm at at least one end of the row of lands so that a protrusion 4 for holding 30% or more of the total quantity of solder on the row of lands is formed thereat. This shape prevents positional shift of the component at the time of mounting, and allows highly accurate positioning of component using a mounter of conventional accuracy thus realizing high density, high quality mounting with high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a land shape such as a printed circuit board on which electronic parts such as ICs, resistors and connectors are surface-mounted by soldering.

[0002]

2. Description of the Related Art As electronic equipment is downsized, made portable, and has higher functionality, the mounting technology that supports it is becoming more sophisticated and diversified year by year. That is, currently, electronic parts such as ICs, resistors and connectors are soldered to lands such as printed circuit boards. However, in the case of QFP or 1005 chips with a pitch of 0.5 mm or less that requires high-density mounting of mounted components, stable mass productivity should be maintained by the batch printing batch reflow surface mounting method using solder cream that has been put into mass production in the past. Has become difficult. Therefore, the solder precoating method has been recently proposed as an alternative method for fine mounting. On page 37 of the magazine Electronic Materials No. 1992.9, a soldering pre-coated substrate manufactured by Furukawa Electric Co., Ltd. using a super soldering method is described, which is a mounting technique for a notebook computer. FIG. 9 is a plan view showing a method of soldering an electronic component (fine QFP) to a wiring board manufactured by the solder precoat method, and FIG. 10 is a side view. The solder lands 5 formed on a wiring board such as a printed board are formed along the wiring pattern. On the upper part of this wiring pattern, the terminal 6 of the flat package component such as the QFP is mounted by a mounter. In order to solder the terminal 6 to the solder land 5, a pre-coated solder 11 which is formed in advance is formed on the solder land 5, and the pre-coated solder 11 is soldered by heating and melting in a reflow furnace.

[0003]

By the way, in the solder by the current solder precoat method, the surface of the solder formed on the copper land 3 has a rounded shape as shown in FIG. Therefore, when placing and soldering the terminals 6 of the close-packed component, it becomes difficult to place the mounted component terminals accurately and stably directly above the solder lands 5, and there is a risk of misalignment.

Further, as shown in FIG. 10, the amount of solder formed on the solder lands 5 varies, so when reflow soldering is performed, such as when there is a small amount of solder remaining and when there is a large positional deviation during mounting. Moreover, since the solder height is low, heat transfer to the solder is poor, and the solder cannot be sucked up to the terminal 6 of the component, resulting in poor soldering. Therefore, as shown in FIG. 12, the surface of the precoat solder 13 formed on the land is flattened,
Moreover, it is considered and proposed that the solder thickness is generally the same. (See Japanese Laid-Open Patent Publication No. 4-318995 and a method for repairing the printed circuit board.) To flatten the solder as in the former, heating is usually performed by a press. For example, it is necessary to flatten the solder by a precoat method as a whole. If you think
It is difficult to flatten a 30 cm square substrate within a few tens of microns over all the lands, and the work itself is a cost-increasing factor and must be of the same quality. Is not suitable for mass production.

The technical problem of the present invention is to solve such problems in the conventional solder joining method by the solder precoating method and to eliminate the component deviation at the time of mounting with a simple land shape.
It is to enable high-quality and high-yield mounting so that positioning can be performed with high accuracy.

[0006]

The shape of the solder precoat land of the present invention is as follows. In a land shape in which solder is applied to a land for soldering, a component is mounted on the solder, then heat-cured, and the component is surface-mounted on a printed circuit board, the amount of solder on the land line is at least at one end of the entire length of the land line. 30% or more of the ridges are ubiquitous.

2. It is characterized in that the convex portions that are ubiquitous on the land row of the means 1 are alternately formed at both ends of the entire length of the land row.

3. The protrusions that are ubiquitous on the land row of the means 1 are formed at every other end at least at one end of the entire length of the land row, and the land width without the ridges is formed at every other end. It is characterized by being longer than the land width.

[0009]

Since the land shape for solder precoating is employed, the surface tension of the molten solder causes a spherical surface to form a convex portion in the place where the land width is large, and the convex portion forms a lead on each side of the QFP to be mounted. Since the mounting position is regulated by the land shape of the printed circuit board in contact with the terminals, the plane formed by all the leads of the QFP is equal to the land position, and when soldering the terminal row of the component, each terminal Stable and accurate positioning can be performed right above.

[0010]

EXAMPLES The present invention will be described in detail below based on examples.

(Embodiment 1) First, an embodiment will be used to explain how the solder precoating method for a wiring board according to the present invention is actually embodied.

FIGS. 1 to 3 are views of the solder shape in the first embodiment of the present invention.

In the land of this embodiment, the convex portions 4 which are ubiquitous on the land row are adjacent to the lead tips 1 of the components mounted on the solder, and the planar position of the components is as shown in FIG. This is the solder precoat land shape 2 formed at the position of the entire length of the land row so as to be surface-mounted on the substrate while controlling the above.
Therefore, if there is an effect of restricting the plane position of the lead tip 1, the number is not limited to a numerical value, but the convex portion 4 having a solder amount of at least 30% or more is required.

The land length is 2.0 mm and the land width is 0.
The land width is set to 16 mm, and the wide land width is set to 0.20 mm so that at least one end of the entire length of the land row forms a convex portion in which 30% or more of the amount of solder on the land row is ubiquitous. A stencil (process lab) in which a pattern was engraved on a glass epoxy circuit board on which 0.3 mm of wiring in which the land shape for solder precoat of this example was arranged was provided by a solder printer (NP-04AN2, manufactured by Hitachi Techno) A eutectic solder cream (MX263-100-FO manufactured by Nihon Solder) was printed while sandwiching a micron product.

Curing was performed in an N2 reflow furnace (manufactured by NRS405 Eitec) whose temperature was controllable while drawing a temperature profile. The initial temperature of 155 degrees Celsius was set as the maximum temperature of 235 degrees Celsius, and curing was performed for 145 seconds in total. Oxygen concentration is 100P
While managing with PM, the solder cream was melted and the solder of this example was deposited on the copper land.

After cooling, a high-viscosity flux (FB212 Harima Kasei) was uniformly applied on the formed pre-coated solder with a dispenser (ML505 made by Musashi Engineering Co., Ltd.) in a thickness of 10 to 50 microns. Furthermore, a chip mounter (CM85C-ME, manufactured by Kyushu Matsushita) was used to mount semiconductor element (0.3 mm pitch QFP) parts. And it joined by the oxygen concentration of 1000PPM with the N2 reflow furnace (made by NRS405 Aitec).

As a result, the fillet shape of the lead terminal 1 having the land shape of the present embodiment was able to surely realize electrical connection and mechanical strength. The occurrence of bridging defects due to excessive application of solder cream particles and heat history, as seen in the conventional printing method, was not observed. Moreover, in the pre-coating method of this embodiment, the amount of solder cream applied is defined according to the land area, so that the volume of the melted solder is properly absorbed, and the effect of this embodiment is that the position accuracy of the lead terminals is guaranteed. Appeared. A decrease in the occurrence rate of bridging defects, which is a characteristic of pre-coated solder, appeared, and there was no problem even if the land interval was narrowed by about 50 microns.

Further, in the solder precoat land shape 2 of this embodiment, since the lead terminal 1 is reliably positioned on the land, the solder pulls the lead terminal 1 together with the flux 14 when the solder melts. Worked. This time, as a method of inspecting the soldering state of the semiconductor element, a method of detecting with laser light and a method of irradiating polychromatic light and processing the image of the image to detect reflected light are both used. The reliable realization was confirmed, and no part of the board was badly soldered.

Examples of heating methods include reflow furnace, N2 reflow furnace, infrared furnace, hot air circulation, laser heating, light beam heating, heating tool, air heater, hot plate, and latent heat of vaporization. These heating methods may be used alone, and may be used in combination or repeatedly. In addition to the eutectic solder, the solder composition that can be used includes those containing 0.1% to 50% of metal components such as tin, bismuth, lead, tin, lead, silver, etc., which can take into account the characteristics of low melting point solder. Is. The flux composition used is pure rosin (R), weakly active rosin (RMA), active rosin (RA), phenolic synthetic resin, fluorine-containing synthetic activator, organic acid, organic salt, etc.
It is also possible to add a component such as a synthetic resin capable of taking into account the characteristics for low residue, or to which a water-soluble inorganic acid / inorganic salt / organic acid / base / organic salt / organic halogen is added.

The soldering characteristics were evaluated. Table 1 shows the results of measurement of bonding strength (g / lead), bridging defect occurrence rate (%), unsoldered defective rate (%), and misalignment defective rate (%).

[0021]

[Table 1]

(Embodiment 2) Next, FIGS. 5 to 7 are views of a solder shape in a second embodiment of the present invention.

In the land of the present embodiment, the protrusions 4 which are ubiquitous on the land row are adjacent to the lead tips 1 of the components mounted on the solder, and regulate the planar position of the lead tips 1. Meanwhile, the solder precoat land shape 8 is formed at the position of the entire length of the land row so as to be surface-mounted on the substrate. The solder precoat land shape 8 was designed so that the convex portions 4 that are ubiquitous on the land row are alternately formed at both ends of the entire length of the land row. Therefore, if there is an effect of restricting the planar position of the lead, the number is not limited to a numerical value, but a convex portion having a solder amount of at least 30% or more is required.

The land length is 2.2 mm and the land width is 0.
15 mm, and the wide land width was alternately set to 0.22 mm so as to form a convex portion in which 30% or more of the amount of solder on the land row is ubiquitous at least at one end of the entire length of the land row. A glass epoxy circuit board provided with 0.3 mm of wiring in which the land shape for solder precoating of this embodiment is arranged is a solder printer (NP-04AN2, manufactured by Hitachi Techno).
Eutectic solder cream (SN63-AM) with a stencil (made by Process Lab Micron) engraved with a pattern
Q-NC52 made by Nippon Superior) was printed.

The composition was cured in an N2 reflow furnace (manufactured by NRS405 A-Tech) whose temperature can be controlled while drawing a temperature profile. The initial temperature of 160 degrees Celsius was set as the maximum temperature of 235 degrees Celsius, and curing was performed for a total of 150 seconds. Oxygen concentration is 100P
While managing with PM, the solder cream was melted and the solder of this example was deposited on the copper land.

After cooling, a high-viscosity flux (FB258 Harima Kasei Co., Ltd.) was uniformly applied to the formed pre-coated solder with a dispenser (ML505, Musashi Engineering Co., Ltd.) in a thickness of 10 to 50 microns. Furthermore, a chip mounter (CM85C-ME, manufactured by Kyushu Matsushita) was used to mount semiconductor element (0.3 mm pitch QFP) parts. And it joined by the oxygen concentration of 1000PPM with the N2 reflow furnace (made by NRS405 Aitec).

As a result, the fillet shape 8 of the lead terminal having the land shape of this embodiment was able to surely realize the electrical connection and the mechanical strength. The occurrence of bridging defects due to excessive application of solder cream particles and heat history, as seen in the conventional printing method, was not observed. Moreover, in the pre-coating method of this embodiment, the amount of solder cream applied is defined according to the land area, so that the volume of the melted solder is properly absorbed, and the effect of this embodiment is that the position accuracy of the lead terminals is guaranteed. Appeared. A decrease in the occurrence rate of bridging defects, which is a characteristic of pre-coated solder, appeared, and there was no problem even if the land interval was narrowed by about 50 microns.

Further, in the solder precoat land shape 8 of this embodiment, since the lead terminal 1 is reliably positioned on the land, there is a self-soldering function that the solder pulls the lead terminal 1 together with the flux when the solder is melted. worked. This time, as a method of inspecting the soldering state of the semiconductor element, a method of detecting with laser light and a method of irradiating polychromatic light and processing the image of the image to detect reflected light are used.
In both cases, it was confirmed that a good fillet shape of the lead terminal was surely realized, and no defective soldered substrate part was found.

Examples of heating methods include reflow furnace, N2 reflow furnace, infrared furnace, hot air circulation, laser heating, light beam heating, heating tool, air heater, hot plate, and latent heat of vaporization. These heating methods may be used alone, and may be used in combination or repeatedly. In addition to the eutectic solder, the solder composition that can be used includes those containing 0.1% to 50% of metal components such as tin, bismuth, lead, tin, lead, and silver, which can take into account the characteristics of low melting point solder. Is. The flux composition used is pure rosin (R), weakly active rosin (RMA), active rosin (RA), phenolic synthetic resin, fluorine-containing synthetic activator, organic acid, organic salt, etc.
It is also possible to add a component such as a synthetic resin capable of adding the characteristics for low residue, or a substance to which a water-soluble inorganic acid / inorganic salt / organic acid / base / organic salt / organic halogen is added.

The soldering characteristics were evaluated. Table 2 shows the measurement results of the bonding strength (g / lead), the bridging defect occurrence rate (%), the unsoldered defective rate (%), and the misalignment defective rate (%).

[0031]

[Table 2]

(Embodiment 3) Next, FIG. 8 is a diagram of a solder shape in a third embodiment of the present invention.

In the land of the present embodiment, the convex portions that are ubiquitous on the land row are adjacent to the lead tips 1 of the components mounted on the solder, and the planar position of the components is regulated so that the land is formed on the substrate. It is a solder precoat land shape formed at the position of the entire length of the land row so as to be surface-mounted.

Solder pre-coating is performed so that convex lands 9 that are ubiquitous on the land row are formed at every other end at least at one end of the land row, and lands 10 that have no ubiquitous convex are formed to be long. The land shape for use was designed. for that reason,
Although there is no particular limitation on the numerical value as long as it has the effect of restricting the planar position of the lead, a convex portion having a solder amount of at least 30% or more is required.

The land length is 2.2 mm and the land width is 0.
15 mm, and at least one end of the entire length of the land row was formed with a wide land width of 0.24 mm so as to form a convex portion in which 30% or more of the amount of solder on the land row is ubiquitous. In the meantime, a land row having a land length of 2.2 mm and a land width of 0.16 mm was formed.

A stencil in which a pattern is engraved on a glass epoxy circuit board provided with 0.3 mm of wiring in which the land shape for solder precoating of this embodiment is provided by a solder printer (NP-04AN2, manufactured by Hitachi Techno) Eutectic solder cream (SN63, sandwiching Process Lab Micron)
-AMQ-NC52 made by Nippon Superior) was printed.

Curing was carried out in an N2 reflow furnace (manufactured by NRS405 Eitec) whose temperature can be controlled while drawing a temperature profile. The initial temperature of 160 degrees Celsius was set as the maximum temperature of 230 degrees Celsius, and curing was performed for a total of 160 seconds. Oxygen concentration is 100P
While managing with PM, the solder cream was melted and the solder of this example was deposited on the copper land.

After cooling, a high-viscosity flux (FB258 Harima Kasei Co., Ltd.) was uniformly applied on the formed pre-coated solder with a dispenser (ML505 made by Musashi Engineering Co., Ltd.) in a thickness of 10 to 50 microns. Furthermore, a chip mounter (CM85C-ME, manufactured by Kyushu Matsushita) was used to mount semiconductor element (0.3 mm pitch QFP) parts. And it joined by the oxygen concentration of 1000PPM with the N2 reflow furnace (made by NRS405 Aitec).

As a result, the fillet shape of the lead terminal according to the land shape of this embodiment could surely realize the electrical connection and the mechanical strength. The occurrence of bridging defects due to excessive application of solder cream particles and heat history, as seen in the conventional printing method, was not observed. Moreover, in the pre-coating method of this embodiment, the amount of solder cream applied is defined according to the land area, so that the volume of the melted solder is properly absorbed, and the effect of this embodiment is that the position accuracy of the lead terminals is guaranteed. Appeared. A decrease in the occurrence rate of bridging defects, which is a characteristic of pre-coated solder, appeared, and there was no problem even if the land interval was narrowed by about 50 microns.

Further, in the solder precoat land shape 9 of this embodiment, since the lead terminal 1 is reliably positioned on the land, there is a self-soldering function that the solder pulls the lead terminal 1 together with the flux when the solder is melted. worked. This time, as a method of inspecting the soldering state of the semiconductor element, a method of detecting with laser light and a method of irradiating polychromatic light and processing the image of the image to detect reflected light are used.
In both cases, it was confirmed that a good fillet shape of the lead terminal was surely realized, and no defective soldered substrate part was found.

Examples of heating methods include reflow furnace, N2 reflow furnace, infrared furnace, hot air circulation, laser heating, light beam heating, heating tool, air heater, hot plate, and latent heat of vaporization. These heating methods may be used alone, and may be used in combination or repeatedly. In addition to the eutectic solder, the solder composition that can be used includes those containing 0.1% to 50% of metal components such as tin, bismuth, lead, tin, lead, and silver, which can take into account the characteristics of low melting point solder. Is. The flux composition used is pure rosin (R), weakly active rosin (RMA), active rosin (RA), phenolic synthetic resin, fluorine-containing synthetic activator, organic acid, organic salt, etc.
It is also possible to add a component such as a synthetic resin capable of taking into account the characteristics for low residue, or to which a water-soluble inorganic acid / inorganic salt / organic acid / base / organic salt / organic halogen is added.

The soldering characteristics were evaluated. Table 3 shows the measurement results of the bonding strength (g / lead), bridging defect occurrence rate (%), unsoldered defect rate (%), and deviation defect rate (%).

[0043]

[Table 3]

Comparative Example Next, a conventional example will be described as a comparative example with reference to FIGS. 9 to 11.

The land length is 2.2 mm and the land width is 0.
The shape of the solder precoat land was designed to be 15 mm. Solder printer (NP-04AN2, made by Hitachi Techno) is equipped with a glass epoxy circuit board with 0.3 mm wiring on which land for solder precoat is arranged.
Eutectic solder cream (SN63-AM) with a stencil (made by Process Lab Micron) engraved with a pattern
Q-NC52 made by Nippon Superior) was printed.

Curing was performed in an N2 reflow furnace (manufactured by NRS405 Eitec) whose temperature was controllable while drawing a temperature profile. The initial temperature of 160 degrees Celsius was set as the maximum temperature of 235 degrees Celsius, and curing was performed for a total of 150 seconds. Oxygen concentration is 100P
While managing with PM, the solder cream was melted and the solder of the present invention was deposited on the copper land.

Then, the current solder pre-coating method for the substrate has a rounded surface of the solder formed on the copper pattern 3 as shown in FIG. Therefore, when the terminals 6 of the fine parts are placed and soldered, the solder land 5
It was difficult to place the terminal directly and directly on the position, and the positional deviation occurred as shown in FIG.

Furthermore, when the mounted parts are affected by the vibration during the operation of the mounter, the solder shape has a rounded surface as shown in FIG.
Will be displaced.

After cooling, a high-viscosity flux (FB258 Harima Kasei Co., Ltd.) was uniformly applied to the formed pre-coated solder with a dispenser (ML505, Musashi Engineering Co., Ltd.) in a thickness of 10 to 50 microns. Furthermore, a chip mounter (CM85C-ME, manufactured by Kyushu Matsushita) was used to mount semiconductor element (0.3 mm pitch QFP) parts. And it joined by the oxygen concentration of 1000PPM with the N2 reflow furnace (made by NRS405 Aitec).

As a result, with respect to the solder joint quality of the manufactured lead terminals of the semiconductor element, due to the convex solder cross-sectional shape, component misalignment occurred in the lead terminals of the semiconductor element. Therefore, delicate flux humidity control, viscosity control, mounter mounting speed / pressure control, substrate warpage correction mechanism, image recognition accuracy improvement, algorithm modification, etc. are required, and post-correction such as bridge failure / floating failure is required. There was a drawback that the manufacturing yield was poor. In addition, as the number of sheets increased, the physical properties of the flux were considered to have changed, which had a great effect on the part fixability such as quantity, viscosity, and tacking.

Examples of heating methods include reflow furnace, N2 reflow furnace, infrared furnace, hot air circulation, laser heating, light beam heating, heating tool, air heater, hot plate, and latent heat of vaporization. These heating methods may be used alone, and may be used in combination or repeatedly. In addition to the eutectic solder, the solder composition that can be used includes those containing 0.1% to 50% of metal components such as tin, bismuth, lead, tin, lead, silver, etc., which can take into account the characteristics of low melting point solder. Is. The flux composition used includes pure rosin (R), weakly active rosin (RMA), active rosin (RA), synthetic resins such as phenolic compounds, fluorine-containing synthetic activators, organic acids, and organic salts.
It is also possible to add a component such as a synthetic resin capable of taking into account the characteristics for low residue, or to which a water-soluble inorganic acid / inorganic salt / organic acid / base / organic salt / organic halogen is added.

The soldering characteristics were evaluated. Table 4 shows the results of measurement of bonding strength (g / lead), bridging defect occurrence rate (%), unsoldered defect rate (%), and deviation defect rate (%).

[0053]

[Table 4]

[0054]

As described above, according to the present invention, in the conventional solder joining method by the solder precoating method, the surface tension of the molten solder in the manufacturing process causes the surface of the solder to be spherical so that the solder cross section forms a convex portion, thereby forming a fine component. The problem of slippage is eliminated, and the invention of a simple land shape eliminates component misalignment during mounting, and realizes high-precision component positioning with the current mounter accuracy, enabling high-density, high-quality and high-yield mounting. This is an industrially useful proposal that eliminates the factors that tend to lead to quality instability and high costs due to maintaining a highly expensive equipment that depends on the mounting machine for high accuracy and maintaining a difficult manufacturing environment.

[Brief description of drawings]

FIG. 1 is a cross-sectional perspective view showing a solder shape by a solder precoating method according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a solder shape according to a solder precoat method of Example 1 of the present invention.

FIG. 3 is a side view showing a solder shape according to a solder precoating method of Embodiment 1 of the present invention.

FIG. 4 is a plan view showing a relative position of a solder shape by a solder precoating method according to a first embodiment of the present invention with respect to QFP.

FIG. 5 is a plan view showing a solder shape by a solder precoating method according to a second embodiment of the present invention.

FIG. 6 is a side view showing a solder shape by a solder precoating method according to a second embodiment of the present invention.

FIG. 7 is a side view showing a solder shape by a solder precoating method according to a second embodiment of the present invention.

FIG. 8 is a plan view showing a solder shape by a solder precoating method according to a third embodiment of the present invention.

FIG. 9 is a plan view showing a solder shape according to a conventional solder precoating method.

FIG. 10 is a side view showing a solder shape according to a conventional solder precoat method.

FIG. 11 is a side view showing a solder shape according to a conventional solder precoat method.

FIG. 12 is a side view showing a flattened solder shape by a solder precoat method of a conventional example.

[Explanation of symbols]

 1 Lead Tip of Fine Pitch QFP 2 Solder Shape by Solder Precoat Method 3 Copper Land 4 Convex part of Precoat Solder 5 Solder Land 6 Terminal 7 Fine Pitch QFP 8 Precoat Land 9 Land 10 Land 11 Precoat Solder 12 Lead Tip of Fine Pitch 13 Pre-coated solder with a flat surface 14 Flux

Claims (3)

[Claims] 1. A land shape in which a solder is applied to a land for soldering, a component is mounted on the solder and then heat-cured, and the component is surface-mounted on a printed circuit board. A solder precoat land shape, characterized in that protrusions are formed in which 30% or more of the amount of solder on a row is ubiquitous. 2. The solder precoat land shape according to claim 1, wherein convex portions that are ubiquitous on the land row are alternately formed at both ends of the entire length of the land row. 3. A land portion is provided with ridges that are ubiquitous on at least one end of the entire length of the land row, and land ridges that are free of ridges are at every other end. The land shape for solder precoat according to claim 1, wherein the land width is longer than the land width not formed.