JPH0143477B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a component mounting method for connecting components to both sides of a circuit board in a high density manner suitable for mass production. FIG. 1 shows a state in which components are connected by a conventional component mounting method, and FIG. 2 shows the main manufacturing process of FIG. 1. The conventional method and its drawbacks will be explained below using FIGS. 1 and 2.

In Figure 1, 1 is a circuit board, 2 and 3 are conductors on both sides, 4 is an individual component such as an electrolytic capacitor having leads 40, and 30 is a leadless chip component such as a rectangular parallelepiped or cylindrical resistor or capacitor. ,
6, the non-conductive adhesive 7 for fixing the component 30 is solder. Here, as the substrate 1, glass epoxy or ceramic is used, and as the conductors 2 and 3, Cu foil is used for the former substrate, and Pd is used for the latter substrate.
-Ag etc. are used. Further, 20 indicates a through hole.

Next, the component mounting process will be explained with reference to FIG. A is a step of applying the non-conductive adhesive 6, in which the non-conductive adhesive 6 is applied only to the inner conductor 3 side of the double-sided conductors of the substrate 1 by printing or using a dispenser. Next, in step P, a component temporary fixing step, the chip component 30 is placed so as to be pressed onto the adhesive, and then hardened and fixed in position. Thereafter, in step D, the leaded component 4 is inserted using an automatic insertion member and fixed in the lead shape as shown in the figure. Next, it is applied to flow solder in step F to connect the parts on the conductor 3 side and complete the assembly.

Next, the disadvantage of these conventional methods is that when using flow soldering, the jet is directed to the back surface of the substrate (i.e., the conductor 3
Since the solder connection is made by pressing down on the side), only one side can be connected. Furthermore, leaded parts 4
The reason why is inserted from the conductor 2 side is not only because it is connected at the same time as the chip component 30 but also because the heat resistance of the component 4 is low. That is, in the dip soldering method in which the entire board 1 is immersed in a molten solder bath, the conductors 2 and 3 are
Although a solder film is obtained on both sides of the solder, it goes without saying that the entire component 4 also needs to be immersed. For example, an electrolytic capacitor is very often used as the leaded component 4, but the maximum allowable melting temperature is usually 85°C, and at a solder melting temperature of 230°C to 250°C, it will puncture almost instantly due to the rapid vaporization expansion of the internal electrolyte. It is clear that this will lead to. In addition, do not directly melt the element body, such as tantalum capacitors, coils, transformers, volumes, relays, etc. that have sliding or moving parts, items that use solder for the element itself, or items that use low heat resistant materials such as plastic. There are extremely many parts with leads 4 that cannot be immersed in the tank.

In addition, when assembling these low heat resistant parts 4 by inserting the chip parts 30 after soldering, these effects can be ignored, but the through holes 20 for lead insertion of the parts 4 are already covered with deep solder. It becomes impossible to assemble.

For these reasons both component 4 and chip component 30 are implemented on the same conductive surface on either side of substrate 1. Therefore, in the conventional method, when it is necessary to mount many components, the board area becomes large, and because only one side is solder-coated, the board becomes warped, causing reliability problems after the components are mounted. Ta. In particular, since chip components 30 such as chip resistors and chip capacitors are not provided with leads, unbalanced thermal and mechanical stress on the front and back surfaces of these boards is absorbed by flexible leads like component 4 with leads. Since this is not the case, it is often directly applied to the thin chip electrode metallization layer, resulting in poor bonding. Furthermore, since connections are made only on one side of the board, all conductor wires that require component connections must be led to this side via through holes. This increases the number of through holes and via holes, and in order to provide these, it is necessary to increase the area of the substrate. Furthermore, it is already well known that an increase in the number of holes and hole density leads to a decrease in productivity and reliability.

Furthermore, the demand for miniaturized packaging has increased in recent years, and when mounting flat pack ICs with many leads coming out from four sides and wireless bonding type flip-chip ICs, which are suitable for highly integrated ICs, these conventional methods cannot be used. None of this was possible. Because of the fine lead pitch (for example, 100 to 200 μι) and electrode dimensions (for example, 100 to 200 μΦ), these require accurate positioning and alignment on the conductor, especially when fixed with adhesive. However, even if these are achieved, flat pack ICs with a large number of pins (for example, 64 pins) with leads coming out from all four sides are likely to bridge or become open because the amount of solder cannot be controlled, and in the case of flip chip ICs, Even the solder bumps were removed by these flows, making it impossible to make a good connection.

This invention was made in order to eliminate the above-mentioned drawbacks, and it is a component mounting method that allows various components to be mounted on conductors on both the front and back surfaces of a board with high reliability, suitable for mass production, and at high density. The purpose is to provide a method.

An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. In the drawings, parts that are the same as or corresponding to those in FIGS. 1 and 2 are given the same reference numerals. Also, Figure 4 is the 3rd
The figure shows the main manufacturing process. In FIG. 3, a leadless chip component 30 such as a chip capacitor is held on the back conductor 3 of the circuit board 1 with a non-conductive adhesive 6. 4 is a component with a low heat resistance lead, such as an electrolytic capacitor, and the lead 40 is inserted into the through hole 20, and the lead 40 is connected on the conductor 3 side with solder 7 like the component 30. On the other hand, the chip component 200 on the conductor 2 side is bonded to the surface conductor 2 with solder paste 70.

Next, the component mounting process will be explained with reference to FIG. A is the process of applying the non-conductive adhesive 6, and the conductor 3
Temporary fixing process of parts dispensed or printed on the side P ₁
Then, for example, the chip part 30 is placed and hardened. Thereafter, in a solder paste printing step S, solder paste is printed on necessary locations such as component mounting portions on the surface conductor 2 of the substrate 1. Step _P2 is a component placement step in which, for example, a chip component 200 is placed on the solder paste. Step K is a heating drying step in which the chip parts 200 placed on the solder paste are temporarily fixed. Next, in process D, the leaded component 4 is automatically inserted using the through hole 20, and both sides are simultaneously joined in a molten solder bonding process, for example, a flow soldering process F. That is, the solder of the solder paste is melted by direct flow soldering on the conductor 3 side and by heat conduction from the conductor 2 side from the 3 side, completing the mounting of components on both sides of the board. In other words, solder paste can be printed on the conductor 2 side in any pattern, so the through hole 20 for inserting the lead 40 of the component 4
The holes can be inserted into an automatic insertion machine without being plugged with solder. Further, since the solder is melted on both sides simultaneously, the warpage of the board 1 is not reduced and the stress on the component 200 side is also reduced. In addition, the solder coats 7, 70 on both sides and the parts 30, 200 connected by them effectively strengthen the board against mechanical stress forcibly applied from the outside, increasing the thickness of the board. The same effect will be obtained and it will be stronger.

In addition, according to an embodiment of the present invention, it is possible to mount components on both surfaces of one circuit board, so the required board size can be reduced to approximately 1/2, resulting in a compact and compact design.
High density packaging is achieved. This reduction in area and double-sided component mounting equivalently increases the strength of the circuit board and improves reliability. In addition, since double-sided mounting is possible in circuit pattern design, the problem of via hole networks where there is no place to drill holes can be solved, and at the same time, the number of through holes can be greatly reduced. Therefore, the degree of freedom in design is improved and reliability can also be improved. Furthermore, there are no particular restrictions on the parts that can be mounted, and any electrical or mechanical parts can be mounted. In other words, cylindrical or rectangular parallelepiped chip capacitors and resistors, as well as mini-molded transistors and flat pack ICs.
Heat-resistant parts with leads such as can be mounted on either the front or back side. In addition, flat pack ICs and wireless bonding type flip chip ICs have recently become particularly dense, with several tens of pins protruding in four directions.
When using, by mounting on the solder paste side, the position can be easily corrected by surface tension without bridging with an accurate amount of solder supply, and the mounting can be performed reliably. Moreover, it goes without saying that it is highly versatile because both the front and back surfaces can be connected in a short time in one flow process. In addition, the supply of non-conductive adhesive and solder paste, the placement of various chip components, and the insertion of individual components are all processes that are easy to automate, making double-sided mounting highly versatile and mass-producible. achieved. As the circuit board, any material that can have conductors formed on both sides and is resistant to soldering heat can be used, including printed circuit boards, ceramic boards, etc., as well as metal core boards such as porcelain boards.

FIG. 5 shows another embodiment of the invention. In the drawings, parts that are the same as or corresponding to those in FIGS. 1 and 3 are given the same reference numerals. In FIG. 5, the circuit board 10 includes surface layer conductors 2, 3, inner layer conductors 8,
A multilayer circuit board with 9 is used. 20
21 indicates a through hole, and 21 indicates a via hole, both of which are appropriately connected to the inner layer conductors 8 and 9 in a circuit.
Further, the component 201 is a flat pack IC, and the component 202 is a flip chip IC. These bonding steps shown in FIG. 5 are carried out on both sides in exactly the same manner as those shown in FIGS. 3 and 4, and produce the same effect. Note that solder paste is used to join the parts on the conductor 2 side (so that they are not fixed with non-conductive adhesive).
Self-position correction can be achieved automatically by surface tension when the solder melts. For this reason, when mounting the flip-chip IC 202 or flat pack IC 201 having extremely high-density and fine electrodes, a reliable connection can be achieved by mounting it on the solder paste side, and double-sided mounting with other components can be easily achieved. In addition, although an example in which a non-conductive adhesive was applied was explained in Figs. 3 and 5, other methods can be used to hold the parts on the back side as long as they do not fall during the flow process _F2 . obtain. That is, in FIGS. 3 to 5, after holding and fixing the electrode part of the back part 30 with a conductive adhesive having solder heat resistance instead of the non-conductive adhesive 6, or by temporarily bonding the electrode part and the conductor 3. After temporarily fixing it by welding, it may be soldered in the same way in flow process _F2 . Alternatively, it is also possible to temporarily fix it using high-melting point solder or a socket for holding parts, but in any case, it is possible to use all the methods to prevent the parts on the back side of the board from falling during the flow process _F2 . Countermeasures are included in this invention. In the embodiment shown in FIG. 4, the solder paste printing step S and the component placement step _P2 may be configured in the same way even if the solder paste is applied to the chip component side in advance and is placed therein. Although the solder paste has been described using a printing method, it goes without saying that the same effect can be achieved by discharging the solder paste using a dispenser, brushing, or the like. Furthermore, in the embodiment shown in FIG.
The conductor 3 side is directly connected to the conductor 2 by flow soldering.
Both sides are joined at the same time by heat conduction from the conductor 3 side, but the heat to melt the solder on the conductor 2 side may be applied by irradiating infrared rays from above the conductor 2 side. In short, if the solder on the conductor 2 side is heated and melted and bonded when the conductor 3 side is heated and bonded with flow solder, the warping that occurs in the circuit board or component can be significantly reduced.

Further, in the embodiment shown in FIG. 3, the chip component 200 placed on the solder paste is temporarily fixed in the heat drying step of step K. At this time,
Depending on the degree of heating and drying, the chip component 200 may be sufficiently bonded to the conductor 2, and even if warping or stress is temporarily applied to the substrate 1 or the chip component 200, both sides of the substrate will be the same in subsequent steps. Since the substrate 1 or the chip component 200 is heated and melted and bonded at the same time, warping or stress temporarily applied to the substrate 1 or the chip component 200 is reduced.

As described above, according to the present invention, there is a step of providing solder paste on the conductor on one side of a circuit board having conductors on both sides, and arranging a component on the solder paste; At least the step of temporarily fixing the components, the solder paste on which the components are placed is heated and dried so that the components are temporarily fixed, and when the components on the other side are joined to the conductor with molten solder. By melting the solder on the one side and joining the part on the one side to the conductor, both sides are joined at the same time, which significantly reduces the warping that occurs when the circuit board is heated and cooled. Since the stress applied to the circuit board can be reduced, the reliability of the circuit board can be significantly improved. Furthermore, since the solder paste is heated and dried so that the parts are temporarily fixed before joining both sides of the board, there is a considerable lag in the joining time between both sides of the board, and the joining stress is reduced. In addition, as a result of placing components on multiple surfaces, high-density mounting is also possible.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a circuit board produced by the conventional method, Figure 2 is a process diagram showing the main manufacturing process of Figure 1, and Figure 3
The figure is a cross-sectional view of a circuit board according to an embodiment of the present invention, FIG. 4 is a process diagram showing the main manufacturing process of FIG. 3, and FIG. 5 is a cross-sectional view of a circuit board according to another embodiment of the present invention. show. In the figure, 1 is a circuit board;
2 and 3 are conductors, 4 is a low heat resistant individual component that cannot be immersed in solder, 7 is solder, 30 is a component, 7
0 indicates a solder paste, 200 indicates a component, P ₁ indicates a temporary fixing process of the component 30, P ₂ indicates a process of arranging the component 200, and F indicates a molten solder joining process. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A step of providing solder paste on the conductor on one side of a circuit board with conductors provided on both sides, placing a component on the solder paste, and temporarily fixing the component on the other side of the board. After heating and drying the solder paste on which the components are arranged so that the components are temporarily fixed, the solder paste on the one surface is heated and dried when the component on the other surface is joined to the conductor with molten solder. A method for mounting components on a circuit board by melting the components and joining the components on one side to a conductor. 2. The method of mounting components on a circuit board according to claim 1, wherein the heat used to bond the components on the other side to the conductor with molten solder simultaneously melts the solder paste to join the components on the one side to the conductor. 3. When the component on the other side is bonded to the conductor with molten solder, the solder paste is melted by heat irradiated from above the component on the one side, and the component on the one side is bonded to the conductor. How to mount components on a circuit board. 4. According to claim 2 or 3, the main body portion of a component that cannot be immersed in solder, such as a chemical capacitor, volume, or relay, is protruded from the side of the circuit board where solder paste is used. How to mount components on the circuit board described.