JPH0438893A - Reflow soldering method for chip-type parts - Google Patents

Abstract

PURPOSE:To eliminate soldering failures by Manhattan phenomena by providing a two-piece foot print, and applying two kinds of solder different in fusing point separately so as to do reflow soldering. CONSTITUTION:A foot print 1 is composed of a pad A11 and a pad B12, which are severally divided approximately equally in twos and are placed apart, and the pad B12 is formed not to connect with wiring 7 and a conductor layer 71. For the application of paste-shaped solder for reflow soldering, to the printed board 8 where solder resist is applied excluding the part of the foot print 1, first paste-shaped solder 22, whose melting point is lower than the solder 21, is applied in thickness of approximately 10mum on the pad B12 by screen printing. Next, solder 21 is applied in thickness of approximately 20mum on the pad A11, and then chip parts 9 are placed accurately so that the terminal end face 91 may not protrude from the foot print 1, and by paste-shaped solder, temporary bonding is performed. Next, the whole is heated to solder them, but heating temperature is controlled in two stages.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a reflow soldering method for chip type components, and aims to provide a soldering method that eliminates soldering defects due to the Manhattan phenomenon that occur during reflow soldering. A reflow soldering method in which a component is mounted on a printed board and soldered to a footprint connected to the wiring, in which the footprint is divided into two parts, pad A and pad B, and solder with different melting points is applied to the pad. A, pad B
In order to perform reflow soldering, pad A should be used as the part connected to the wiring, and pad B should be used as the non-connected part, and pad A should be filled with solder with a higher melting point, and pad B should be filled with solder with a higher melting point than the solder. Configured to apply a low level of solder and perform reflow soldering.

[Industrial application field]

The present invention relates to a method for reflow soldering chip-type components.

Electronic circuit devices are constructed by mounting various parts, including ICs, on printed circuit boards.As component elements become smaller, the parts also become smaller and more sophisticated, and leads are now mounted on flat surfaces. There is a shift toward surface-mounted components, in which leads are eliminated, or at least planar terminals are formed on the bottom surface and connected by soldering to the surface of a printed circuit board.

Among these latter components, chip-type components with a low degree of integration have extremely small external dimensions and require careful soldering.

[Conventional technology]

FIG. 2 shows an example of a conventional method for soldering chip-type components.

Conventionally, flow soldering has been used for soldering on printed circuit boards, but for surface mount components, unless the components are specially fixed to the printed circuit board, the solder flow will cause the components to move. It's impossible. In addition, in chip type components, protection means for component elements are simplified and miniaturized, and as a result, they are inferior in heat resistance and the like compared to conventional lead terminal type components, and flow soldering may not be possible.

As shown in FIG. 2, such a chip-type component 9 has a small rectangular parallelepiped outer shape, and a metal surface is exposed on the side surface of the opposite end to form a surface terminal 91 for connection.

A connection footprint 15 connected to each wiring 7 is provided on the printed board 85 in a pattern slightly larger than the shape of the surface terminal 91 to match the arrangement of the surface terminal 91 to be connected.

Soldering is carried out by applying paste-like solder 21 to a predetermined thickness on the footprint 15 of the printed board 85, which has been coated with solder resist except for the solder resist 15. The chip type component 9 is placed accurately so that it does not protrude from the area 15.

Then, the chip type component 9 is temporarily adhesively fixed by the paste-like solder 21.

Next, soldering is performed by a reflow soldering method using an entire heating method in which the entire printed board 85 is heated to melt the solder 21 .

In this way, the chip type component 9 can be easily soldered to the printed board 85 without any special fixing treatment.

[Problem to be solved by the invention]

However, ■ defective soldering occurs due to the so-called Manhattan phenomenon, in which the chip type component 9 stands upright on one footprint 15, floats up from one footprint 15, or protrudes from one footprint 15. Was.

■ Items with defective soldering have to be repaired individually, which requires a lot of man-hours and is not desirable from the viewpoint of reliability.

There are other problems.

In view of these problems, it is an object of the present invention to provide a soldering method that eliminates soldering defects due to the Manhattan phenomenon that occur during reflow soldering.

[Means for Solving the Problems] The above objectives are as shown in FIG. 1: [1] Reflow soldering in which a chip type component 9 is mounted on a printed board 8 and soldered to a footprint 1 connected to a wiring 7. The method comprises: converting footprint 1 to band All
This is achieved by the reflow soldering method for chip-type components of the present invention, in which solder 2L22 having different melting points is separately applied to pad All and pad B12, and reflow soldering is performed. Ru.

[21 Also, the part connecting the band All to the wiring 7,
It is also possible to use a method in which reflow soldering is performed by leaving the band B12 as an unconnected part, applying solder 21 with a high melting point to the pad All, and applying solder 22 having a lower melting point than the solder 21 to the pad B12.

(Function) In other words, one of the small pads that divides the footprint 1 into two.
Since the chips are first soldered at a low temperature, it is difficult for the chip type component 9 to move when the solder melts, and even if the final soldering is subsequently performed using higher temperature solder, the Manhattan phenomenon will not occur during the final soldering.

In reflow soldering in which preheating is performed using an overall heating method, the Manhattan phenomenon causes small and light chip-shaped components 9 to move due to the difference in cohesive force of molten solder.

Therefore, the solder 21 of the surface terminal 91 at the end of the chip type component 9
This occurs more often when the amount of solder 21 is large (and there is a time lag between the terminals when melting the solder 21).

Therefore, footprint 1 was divided into two parts, and solder 2L22 with different melting points was applied separately, such as high temperature and low temperature.
During reflow soldering, only the low-temperature solder 22 melts first, resulting in a small amount of solder only on the divided pad B12, and the cohesive force of the solder is sufficiently small, and the unmelted high-temperature solder 21
are in a state where the adhesive action is effective, and even if there is a time lag in the melting of the solder 22 between the pads B12, the chip type component 9 can be reliably immovable.

The solder 21 of pad All is also melted by the subsequent heating, and soldering is performed with a sufficient amount of solder, but in this state, the solder 22 is already in an adhesive state due to its cohesive force, and the melting of the solder 21 adds to the melting. Even if a time difference occurs, the Manhattan phenomenon cannot occur in the chip type component 9.

Note that it is preferable to suppress the time difference between melting of the first low-temperature solder 22 as much as possible, and for this reason, the pad B12 to which the solder 22 is applied is only a pad and is not connected to the wiring 7, so that the thermal This eliminates the influence and takes into consideration temperature uniformity, and is extremely effective when the wiring 7 is a grounded conductor layer.

In this way, it is possible to provide a method for soldering chip-type components that eliminates soldering defects due to the Manhattan phenomenon that occur during reflow soldering.

〔Example〕

The present invention will be specifically described below with reference to embodiments shown in the drawings. The same reference numerals indicate the same objects throughout the figures. FIG. 1 shows an embodiment of the present invention.

The soldering method will be explained in order with reference to FIGS. 1(a) to 1(C).

The preparation stage is as shown in Figure (a), where the two-terminal chip type part 9
has the external shape of a small rectangular parallelepiped, and a metal surface is exposed on the side surface of the opposite end to form a surface terminal 91 for connection.In this embodiment, the chip has a mounting area of I This was applied to mold part 9.

On the printed circuit board 8, a connecting flap print 1 connected to each wiring 7 or a wide conductor layer 71 such as a ground conductor layer is patterned slightly larger than the shape of the surface terminal 91 to match the arrangement of the surface terminal 91 to be connected. It is set up as follows.

However, in the present invention, this footprint 1 is divided into approximately equal halves to be composed of a band All and a pad B12 with a gap between them, and the pad B12 is formed so as not to be connected to the wiring 7 or the conductor layer 71.

To apply paste solder for reflow soldering, paste solder 22 having a lower melting point than solder 21 is first applied to pad B12 on printed board 8 on which solder resist has been applied except for the footprint l. is applied to a thickness of approximately 10μ by screen printing. Next, after applying solder 21 to a thickness of about 20 μm to the band All, place the chip type component 9 accurately so that the terminal surface 91 does not protrude from the footprint 1, and apply paste-like solder. Temporary adhesive fixation is performed.

Next, the whole is heated and soldered, and the heating temperature is controlled in two stages.

Initially, the temperature is maintained at 150"C for about 200 seconds. In this state, as shown in FIG.
The temperature of the soldered part is sufficiently uniform.

Next, raise the temperature to about 215°C and heat for about 10 seconds. In this state, as shown in Figure (C), the solder 21 of the pad All also melts and the entire footprint 1 is soldered.

After that, it is cooled and soldering is completed.

The above embodiment shows one example, and the shapes, dimensions, and heating temperature control values of each part are not limited to the above.

Further, the solder 21 and 22 may be applied by any other method, and of course, there is no problem in applying any solder first.

Furthermore, the heating temperature may be controlled in three stages: preheating, melting of the low temperature solder 22, and melting of the high temperature solder 21.

〔Effect of the invention〕

As described above, the reflow soldering method for chip-type components of the present invention can eliminate soldering defects caused by the Manhattan phenomenon that occur during soldering, reduce post-soldering inspection and rework, and reduce costs. The effect is remarkable.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows a conventional method for soldering chip-type components. In the figure, 1.15 is the footprint, 7 is the wiring, 8.85 is the printed board, 9 is the chip type component, 11 is the bad A,
12 is pad B, 21.22 is solder,
71 is a conductor layer, and 91 is a surface terminal.

Claims (1)

[Scope of Claims] [1] A reflow soldering method in which a chip type component (9) is mounted on a printed board (8) and soldered to a footprint (1) connected to a wiring (7), the foot Print (1) on pad A (11) and pad B (
solder (21) and (22) having different melting points are applied to the pad A (
11) A reflow soldering method for chip-type components, characterized in that the method is applied separately to pad B (12) and reflow soldered. [2] The pad A (11) according to claim [1] is connected to the wiring (
7), pad B (12) is left unconnected, pad A (11) is filled with solder (21) with a high melting point, and pad B (12) is filled with solder (21) with a lower melting point than the solder (21).
22) A reflow soldering method for chip-type components, characterized by applying 22) and performing reflow soldering.