JPH0547997B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for automatically mounting reed-lith type surface mount components such as chip components on a printed circuit board by reflow soldering.

[Conventional technical background and its problems] Conventionally, methods have been proposed in which leadless (chip) small electric components are reflow soldered to both sides of a printed circuit board with the premise of high-density automatic mounting.

An example of such a method is explained with reference to FIG. 2. First, the soldering paste 1 is printed on the first surface of the printed circuit board 5 (FIG. 2 a), and then the small leadless component 2 is mounted on the same surface. After the process of melting the solder in a reflow oven (Fig. 2b), the board 5
Turn the front and back sides of the board, print the soldering paste 3 on the second side (Fig. 2C), mount the small leadless component 4, and melt the solder in a reflow oven (the second
Figure d).

Furthermore, for non-leadless components that are not subjected to automatic mounting, this type of mounting board has been obtained through a manual retrofitting process (FIG. 2e) after the reflow process is completed. Note that the solder on both sides of the board had no difference in melting point.

With this method, mounting can be performed on both sides without using adhesive for temporary fixing, and in the process shown in FIG.
Since the parts on the top side were already soldered, there was no risk of them falling off, and even if the solder on the first side on the bottom side melted during the process shown in Figure 2 (d), the surface tension of the molten solder would prevent the lead from falling. The parts were held and no parts fell.

However, with the miniaturization of consumer electronics, the idea of making components leadless (chip) has traditionally been aimed at thinner parts, so there was no problem, but recently with the aim of increasing density and fully automating the mounting process, it has been Leadless technology is also progressing for large parts (hereinafter referred to as irregularly shaped parts), which have been targeted at large parts.

Conventionally, such components that were retrofitted include electrolytic capacitors, which have heat resistance issues, and jacks, which require manual operation from the outside after mounting.
Switches, polymers, etc., and these leadless devices are generally relatively large and heavy due to their heat resistance and operability.

For this reason, when such irregularly shaped leadless components are automatically mounted, those on the lower surface cannot rely on the surface tension of the molten solder like small leadless components, and often fall during the melting process.

[Object of the invention] The present invention is applicable to
The purpose of this paper is to propose an automatic mounting method that enables stable mounting of irregularly shaped leadless components.

[Summary of the Invention] The electrical component mounting method of the present invention includes the steps of mounting and soldering electrical components on both sides of a printed circuit board.
In the method for mounting an electrical component, the method includes the steps of: soldering the electrical component on a first surface by reflow processing, then inverting the printed circuit board so that the second surface is facing up, and soldering the electrical component using reflow processing; The solder on the first surface and the second surface have a difference in melting point, and the second surface is made to have a relatively low melting point solder, and the solder on the first surface of the printed circuit board, which becomes the lower side by the above reversal, is The device is characterized in that only small or thin electrical components are mounted, and large irregularly shaped leadless components are mixedly mounted on the second surface of the printed circuit board.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram of an embodiment of the present invention. In FIG. 1a, solder 8 paste is printed on the first surface of a printed circuit board 15, and then a small leadless component 9 is mounted.

This type of component 9 is a rectangular leadless component such as a resistor, a ceramic capacitor, or a flat package IC, which is a thin component whose mounting height is not very high. and each electrode is soldered as shown in FIG. 1b.

In FIG. 1c, the substrate 15 is turned over and solder 10 is printed on the second side.

Solders 8 and 10 have a slight difference in melting point with solder 10 having a relatively low melting point, and are selected to the extent that the heat condition of the component and mechanical strength will not deteriorate.
Use solder that has a melting point at or near the pb-Sn binary eutectic point.

Next, a process of mounting the parts on the second side is performed,
Irregular leadless components 11, 12, 13 such as a relatively large jack 13, a switch 12, and a relatively large capacitance vertical chip type DC electrolytic capacitor 11.
However, general small leadless components with low mounting height14
etc., by an automatic loading machine.

After this, it is passed through a furnace and subjected to heat treatment,
The solder 10 is melted and the mounting process is completed (FIG. 1d).

The steps of the embodiment are configured as described above.

For this reason, the target large, heavy, irregularly shaped leadless parts will not turn over after being mounted and will be prevented from falling, and the second side will be heated during the temperature raising process during reflow. (furnace entering process) is done only once, which reduces thermal deformation of this type of parts which are easily affected by heat due to their relatively large size.
For components that require manual operation from the outside after mounting, deterioration in positional accuracy, durability, appearance, etc. relative to the housing side is also prevented.

Furthermore, since the solder on the second surface side has a relatively low melting point, the heating temperature can be set low, and the effects of heat on the components are further alleviated, which is favorable.

On the other hand, chip capacitors that are designed for reflow are designed to prevent electrolyte leakage due to increased internal pressure.
Generally, heat resistance measures are taken to some extent, but it is desirable to minimize the effects of heat exposure from the viewpoint of the durability of the element itself, and small-diameter chip-type electrolytic capacitors are also suitable for such mixed mounting surfaces. You can also arrange it.

In addition, especially if an implementation like the example is adopted,
Since such large components are mounted intensively on one side, the total mounting height on both sides, that is, the sum of H (surface mounting height with mixed leadless components) and h (surface mounting height without mixed mounting in the case of the example) is It is suppressed to a minimum and is convenient as a mounting board used in small devices and the like.

[Effects of the Invention] As described above, according to the present invention, irrespective of the shape of the irregularly shaped leadless component or the operating conditions of the furnace, it is possible to simultaneously prevent the irregularly shaped leadless component from falling and reduce the influence of heat exposure.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing a mounting method according to an embodiment of the present invention, and FIG. 2 is a process diagram showing a conventional example. 5, 15...Printed circuit board, 1, 3, 8, 10
... Solder, 2, 4, 9, 14 ... Small leadless parts, 11, 12, 13 ... Irregular leadless parts.

Claims (1)

[Claims] 1. When mounting and soldering electrical components on both sides of a printed circuit board, the electrical components are soldered on the first side by reflow processing, and then the printed circuit board is turned over and the second side is placed upward. In a method for mounting electrical components, which includes a step of soldering the electrical components by reflow processing, the solder on the first surface and the second surface have a melting point difference, and the second surface is relatively low melting point solder. At the same time, only small or thin electrical components are mounted on the first surface of the printed circuit board, which becomes the lower side by the above reversal, and large irregularly shaped leadless components are mounted on the second surface of the printed circuit board. An automatic mounting method for electrical components characterized by mixed mounting of electrical components.