JPH0442838B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an electronic component suitable for attaching an electronic component such as an IC component with a very narrow gap between lead terminals to an insulating substrate by soldering. This relates to the installation method.

[Prior art] An insulating substrate (hereinafter referred to as a printed wiring board) on which a conductive pattern is formed using copper foil, plating, etc.
When mounting an electronic component with narrow spacing between lead terminals, the spacing between soldering lands of the conductor pattern to which the lead terminals are soldered becomes very narrow.
When the distance between adjacent lands (land spacing) becomes narrower, even if a soldering resistive layer called solder resist is formed between the lands to prevent solder adhesion, the soldering resistive layer will extend over the soldering resistive layer to the adjacent land.
Bridging between lands often occurs due to solder.

Therefore, various techniques have been proposed to prevent such bridging caused by solder. For example, in the technology shown in Japanese Patent Publication No. 54-41102,
By forming a wall by forming a second soldering resistance layer for preventing bridging on the first soldering resistance layer made of solder resist formed between the lands, solder can easily connect the adjacent lands. I try not to let it get too long. Further, Japanese Patent Application Laid-open No. 114293/1983 discloses a technique for forming walls by directly forming a soldering resistive layer for preventing bridging, without using a solder resist, in areas where the land spacing is narrow.

FIG. 4 shows an example using the former conventional technology.
This shows the state when the lead terminals of IC components are soldered. In the figure, 1 is an insulating substrate, 2
1 is a through hole passing through the board 1, and 3 is a lead terminal of an IC component. Reference numeral 4 denotes an annular soldering land formed on one upper surface of the substrate 1 so as to surround one opening of the through hole. Although not shown, a printed wiring pattern is connected to this land 4, and a conductor pattern is formed by the land 4 and the wiring pattern. 5 is land 4
6 is a first soldering resistance layer made of solder resist formed between the land 4 and the part where soldering is not required, and 6 is a first soldering resistance layer formed in the part where the land interval is narrow to prevent the solder from crossing over. This is the soldering resistance layer of No. 2. 7 is solder that is applied by dipping the surface on which the conductive pattern is formed in a molten solder tank or a jet solder tank, and electrically and mechanically connects the lead terminal 3 and the land 4. It is.

In reality, it is difficult to accurately print the second soldering resistance layer 6 on top of the first soldering resistance layer 5.
Printing misalignment often occurs. Further, the amount and viscosity of the solder in the solder tank and the properties of the flux are not always constant, and it is difficult to keep the solder always within the area partitioned by the second soldering resistance layer 6.
For example, if the second soldering resistive layer 6 is printed so as to largely overlap the land 4 due to printing misalignment, the soldering resistive layer 6 will come too close to the lead terminal 3, and the solder will spread as shown at 7'. Second soldering resistance layer 6
It may even adhere to the top surface. Also, if the viscosity of the solder is too high, the solder may adhere to the top surface of the second soldering resistance layer 6 as shown by 7'', and in the worst case, a complete short circuit may occur. Furthermore, even if the solder stays within the area partitioned by the second soldering resistive layer 6, the flux residue generated during soldering will spread over the second soldering resistive layer 6 as shown by reference numeral 8. Furthermore, as shown by reference numeral 9, solder grains may remain on the resistive layer 6. In this way, excess solder 7',
If excess solder 7'', 9 and flux residue 8 remain on the second soldering resistance layer 6, the insulation distance between the lead terminals becomes short. It is a matter of course that the insulation distance is shortened, but the insulation distance is also shortened if the flux residue 8 remains. This is because flux residue is originally non-conductive, but solder components may remain in flux residue, and flux residue remaining in areas where the temperature rises will soften and gradually expand. This is because it tends to spread. Therefore, in order to improve the reliability of the product, it has been necessary to remove unnecessary solder and flux residues by a troublesome process such as cleaning after the soldering process. However, if flux residue is removed using a cleaning solution, the cleaning solution may reduce the adhesive strength between the conductor pattern and the substrate, or cause chemical and physical deterioration to electronic components and insulating substrates. Generally, cleaning is rarely performed after the soldering process. Therefore, during long-term use, the dielectric strength decreases, and if dirt or dust adheres to the resistance layer, short circuits may occur between the lead terminals, resulting in a lack of reliability.

Therefore, in order to solve this problem, as shown in Japanese Patent Application Laid-Open No. 57-87195, a removable second solder resistive layer is used in place of the second solder resistive layer described above, A method has been proposed in which the second soldering resistance layer is peeled off after soldering. In the method disclosed in this publication, a second removable solder resistor layer is formed using the same mask used to form the first solder resistor layer. By using a removable second soldering resistance layer in this way and peeling off the second soldering resistance layer after soldering, unnecessary substances (solder and flux residue) that shorten the insulation distance between lands can be removed. can be easily removed.

[Problems to be Solved by the Invention] However, if the peelable second soldering resistance layer is formed using the same mask as the mask used to form the first soldering resistance layer, the following problem occurs.

Using the same mask, the second solder resistive layer, which is substantially removable, will be located only on top of the first solder resistive layer. Although the peelable second soldering resistance layer has the property of being easy to peel, it can be placed on a soldering land made of copper foil or the like, or placed on a first soldering resistance layer made of an insulating resin. It is less likely to peel off when it is located on the first soldering resistance layer. The reason for this is that when comparing the surface roughness of the soldering land and the first soldering resistance layer, the surface of the first soldering resistance layer is rougher, and the adhesion strength of the second soldering resistance layer is higher. It is presumed that this is related to the materials of both resistance layers. When the distance between soldering lands is wide, the width of the second soldering resistive layer located between the lands also becomes wide, so that the close contact between the first soldering resistive layer and the second soldering resistive layer is reduced. Even if the force is somewhat high, it is easy to peel off the second soldering resistance layer. However, when the land spacing becomes narrower, the width of the second soldering resistance layer located between the lands becomes narrower, and the adhesion between the first soldering resistance layer and the second soldering resistance layer becomes larger. As a result, there is a problem in that the second soldering resistance layer cannot be peeled off smoothly.

If the same mask is used, the second soldering resistive layer will be formed even in areas where the land spacing is wide and the second soldering resistive layer is not required.
There is a problem in that the material for making the soldering resistive layer is wasted, and there is also a problem in that unnecessary peeling operations are increased.

The resin paint forming the second soldering resistance layer is
Due to its relationship with surface tension, it has the property that the narrower the coating width, the thinner the thickness. Therefore, when the land spacing becomes narrower, the width of the first soldering resistor layer becomes narrower, and as a result, the width and thickness of the second soldering resistor become narrower, and the thickness of the second soldering resistor becomes smaller. There is a problem that the bridging prevention function deteriorates.

The purpose of the present invention is to provide a method for attaching electronic components that can reliably peel off the second soldering resistance layer without wasting material or requiring unnecessary peeling work.

[Means for Solving the Problems] In the present invention, a peelable second soldering resistance layer is formed between a plurality of soldering lands having narrow land intervals so as to overlap with a part of the soldering lands.

[Function] The part where the peelable second soldering resistance layer overlaps the soldering land is more easily peeled off than the part where it overlaps with the first soldering resistance layer. do. Therefore, when peeling off the part of the peelable second soldering resistance layer formed between the soldering lands with narrow land spacing, the peeling first starts from the part that overlaps with a part of the soldering land.
The peeling promotes peeling of the portion overlapping with the first soldering resistance layer, and the second soldering resistance layer can be easily peeled off. Therefore, the second soldering resistance layer can be peeled off more smoothly than in the past.

Further, in the present invention, by simply forming a removable second soldering resistance layer between a plurality of soldering lands with narrow land intervals that originally require a second soldering resistance layer, the first soldering resistance layer can be easily removed. Since the second soldering resistance layer is not entirely formed on the resistance layer, there is an advantage that the material of the second soldering resistance layer is not wasted and unnecessary peeling work is not required.

Furthermore, even if the spacing between the lands becomes narrower, the width of the second soldering resistance layer between the lands can be increased by the amount that overlaps with the soldering lands, so the thickness of that part can be increased and the second soldering resistance layer can be made wider. This has the advantage of suppressing deterioration of the bridging prevention function of the resistive layer.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows one aspect of the process when carrying out an embodiment of the method of the invention. Note that the first
In the figure, the difference from the conventional technique shown in FIG. In the method of the present invention, the soldering resistance layer 10 is peeled off after the soldering process. As a material for forming the peelable soldering resistance layer 10 for preventing bridging, a known peelable resin can be used.
For example, a thermosetting peelable solder resist sold under the trademark "Pillcoat", which is made by mixing 55 wt% of vinyl resin, 42 wt% of ester plasticizer, and 3 wt% of pigment, can be used.

The steps of an embodiment of the present invention will be described below with reference to FIG. First, the manufacturing process of the printed wiring board will be explained. An insulating substrate 1 made of copper foil on one side is etched to form a predetermined conductor pattern, and then through holes 2 are formed using a drill or the like. Then, by screen printing, a solder resist is applied between the lands 4 and to areas where solder is not to be attached, thereby forming the first soldering resistance layer 5. After passing through a prescribed drying process, apply a plastic solder resist of a prescribed viscosity to areas with narrow land spacing (e.g. 0.5
The film thickness is 150 mm.
A peelable soldering resistance layer 10 for preventing bridging with a thickness of ~200 μm is formed. Then, the board is placed in a constant temperature oven at 140° to 150° and heated for a predetermined time to form a soldered resistor layer 10.
harden. The soldering resistance layer 10 is formed so as to partially overlap the land 4. This is to increase the width of the soldering resistive layer 10 so that the thickness of the soldering resistive layer 10 can be increased as much as possible, and it can be peeled off as easily as possible in the subsequent peeling process. .

The lead terminals 3 of the electronic components are attached to the printed wiring board in the following manner. First, the lead terminal 3 of the electronic component is inserted into the through hole 2 of the printed wiring board, and soldering is performed using, for example, reflow soldering, so that the solder 7 is attached between the end of the lead terminal 3 and the land 4. In this soldering process, the solder may reach the top of the soldering resistive layer 10 as shown by the symbol 7', or the solder grains may adhere to the soldering resistive layer 10 as shown by the symbol 9. Sometimes I do. Further, as shown by reference numeral 8, a large amount of flux residue may remain.

Therefore, after the soldering process, in the method of the present invention, a process of peeling off the soldering resistance layer 10 for preventing bridging is performed. When the soldering resistive layer 10 is peeled off, it is usually peeled off with tweezers or by hand. However, if there is a large amount of excess solder, it may be difficult to peel it off, but in that case, the soldering resistive layer 10 is peeled off while cutting or melting the excess solder using a soldering iron or the like.

FIG. 2 shows an undesirable example in which a frame portion 11 is formed around the soldering resistance layer 10 for preventing bridging. As shown in this figure, avoid the soldering land 4 and
1 and the soldering resistance layer 10, the effect of the present invention cannot be obtained. Therefore, when forming the frame portion 11, it is necessary to form a part of the land 4 and the soldering resistance layer 10 as shown in FIG. It is preferable that they overlap.
This frame portion 11 is provided so that even when the width dimension of the resistance layer 10 for preventing bridging is made small, a certain amount of force can be applied to the resistance layer 10 to facilitate peeling. . In particular, if the frame portion 11 is made large enough to be pinched with fingers, the soldering resistance layer 10 can be easily peeled off. If the soldering resistance layer 10 is formed in a linear pattern as in this example, printing misalignment can be reduced.

Further, FIG. 3 shows an example of another pattern of the soldering resistance layer 10. In this figure, the first soldering resistive layer 5 is not provided under the soldering resistive layer 10, and the soldering resistive layer 10 does not overlap with the lands 4, but this pattern is applied to the present invention. In this case, it is necessary to provide the first soldering resistive layer 5 under the soldering resistive layer 10 and to overlap a part of the soldering resistive layer 10 with the land 4.

[Effects of the Invention] When the peelable second soldering resistance layer is formed between a plurality of soldering lands with narrow land intervals so as to overlap with a part of the soldering lands as in the present invention, the following excellent effects can be achieved. effect can be obtained.

(1) When peeling off the part of the peelable second soldering resistor layer formed between soldering lands with narrow land spacing, peeling first starts from the part that overlaps with a part of the soldering land. Since the peeling promotes peeling of the portion overlapping with the first soldering resistive layer, the second soldering resistive layer can be easily peeled off, and the peeling of the second soldering resistive layer is faster than in the past. can be done smoothly.

(2) By simply forming a removable second soldering resistance layer between a plurality of soldering lands with narrow land spacing that originally required a second soldering resistance layer, the first
Since the second soldering resistive layer is not entirely formed on the soldering resistive layer, there is an advantage that the material of the second soldering resistive layer is not wasted and unnecessary peeling work is not required.

(3) Even if the spacing between the lands becomes narrower, the width of the second soldering resistance layer between the lands can be increased by the amount that overlaps with the soldering lands, so the thickness of that part can be increased to increase the width of the second soldering resistance layer between the lands. This has the advantage of suppressing the deterioration of the bridging prevention function of the soldering resistance layer No. 2.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of a step when carrying out the method of the present invention, FIGS. 2 and 3 are plan views showing other patterns of a removable solderable resistance layer,
FIG. 4 is a sectional view showing a conventional technique. 1...Insulating board, 2...Through hole, 3...
Lead terminal, 4... Land, 5... First soldering resistance layer, 6... Second soldering resistance layer, 7, 7',
7″, 9…Solder, 8…Flux residue, 10
...Peelable second solder resistive layer.

Claims (1)

[Scope of Claims] 1. The solder of the insulating substrate in which a plurality of soldering lands are formed so as to respectively surround the openings of a plurality of through holes, and a first soldering resistance layer is formed between each soldering land. A second soldering resistance layer for bridging prevention that is peelable is formed on the bonding resistance layer, and the leads of the electronic component are arranged so that the ends thereof protrude from the surface of the insulating substrate on which the soldering lands are formed. Inserting terminals into the plurality of through holes, soldering the end portions of the lead terminals to the soldering lands, and peeling off the second soldering resistance layer, which can be peeled off after soldering, to the insulating substrate. A method for attaching an electronic component to an electronic device, characterized in that the second removable soldering resistance layer is formed between a plurality of soldering lands with narrow land intervals so as to overlap with a part of the soldering lands. How to install parts. 2. The method of attaching an electronic component according to claim 1, wherein the second soldering resistance layer has a large area portion located away from a portion between the plurality of soldering lands.