JPH0758830B2 - Printed circuit board soldering method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new printed circuit board soldering method.

[0002]

2. Description of the Related Art Conventionally, as means for soldering electronic parts to a printed circuit board by using a reflow oven, as shown in FIG. 5, a cream solder printer 1 prints cream solder on the printed circuit board. Then, an electronic component is mounted on the mounter 2, and the solder is heated and melted in the reflow furnace 3 to bond the printed circuit board and the electronic component.

However, with the recent improvement in technology, the lead pitch of electronic parts has become narrower than 0.3 mm, and cream solder printing for such fine pitch parts is technically impossible. There is. That is, the particle size of the commonly used cream solder is 20 to 50 μm, while the plate hole provided in the metal mask for printing the cream solder on the printed circuit board is small and thin. For example, there is a metal mask having a plate hole with a thickness of 100 μ.
The amount of solder printed by passing the solder particles is extremely small due to the viscosity of rosin contained in the cream solder, which causes soldering failure.
Currently, for fine-pitch electronic components, the printing method of cream solder using a metal mask is not used.

Therefore, in the present situation, the printed circuit board copper is plated with solder, cleaned and dried, and delivered to the electronic device manufacturer from the printed circuit board manufacturer. In this electronic device manufacturer, the plated solder is used. Adhesive flux is applied to the surface, electronic parts are mounted on this, and soldering is performed in a reflow furnace. However, with such means, it is necessary to use flux because soldering failure due to oxidation of the plated solder surface is unavoidable.
After the completion of soldering, there remains a problem that cleaning and removing work of a residue by a solvent or rosin contained in the flux is required.

An object of the present invention is to use no flux at the time of reflow soldering an electronic component to a printed circuit board, or to set the amount of rosin (solid content) to about 2 wt% which does not require residual cleaning and removing means. The soldering method uses a weak flux and does not require a cleaning means for removing residues and solder balls, and a soldering lead pitch of 0.3 m in which cream solder cannot be printed.
An object of the present invention is to provide a soldering method for a printed circuit board, which allows reflow even with m to 0.15 mm.

[0006]

SUMMARY OF THE INVENTION The structure of the present invention for solving the problems of the prior art is the first step of soldering a printed circuit board in an inert gas atmosphere, and the printed circuit board is half-turned in an air atmosphere. The second step, a third step of applying an adhesive for temporarily fixing electronic parts to the required parts of the printed board, the fourth step of temporarily fixing the electronic parts to the printed board through the adhesive, in an inert gas atmosphere The fifth step of reflow soldering is continuously performed in a series of lines, and a weak flux is applied to the printed circuit board as a preceding step of the first step.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, details of embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory view of an apparatus used for carrying out the method of the present invention, FIG. 2 is an explanatory view of an apparatus of another embodiment, FIG. 3 is an explanatory view of a solder coating machine, and FIG. 4 is a solder film thickness and residual oxygen concentration. It is a characteristic view which shows a relationship.

FIG. 1 shows an apparatus for carrying out the soldering method according to claim 1, 11 is a soldering machine, 12 is a reversing machine, 13 is an adhesive applicator (dispenser), and 14 is electronic component mounting. The machines (mounters) and 15 are reflow furnaces, and are independent of the carriers 11a and 1 of the printed circuit board 16.
2a, 13a, 14a, 15a are provided and are continuously provided on a series of lines.

As is apparent from FIGS. 1 and 3, the soldering machine 11 is provided with the carrier 11a in a hermetically sealable housing 17 and a printed circuit board 16 from one side to the other side.
Are transported. Then, the carrier 11
A pre-heater 18 for preheating the printed circuit board 16 and a solder bath 19 having a jet nozzle are disposed below a. In addition, the inside of the housing 17 is configured to maintain an inert atmosphere such as nitrogen gas, and to prevent outside air from flowing into the housing through the supply port and the discharge port of the printed circuit board 16. There is a shutter mechanism.
In this embodiment, the entire housing is shown as an inert gas atmosphere, but the carrier 11a of the printed circuit board 16 is arranged in a dome (not shown) provided in the housing 17, and this dome is used. There is also a convenient method in which the amount of the inert gas used is reduced by setting the inert gas atmosphere.

The reflow furnace 15 includes a printed circuit board 16
It is composed of a preheating unit 20, a heating unit 21, and a cooling unit 22, and the inside of the housing 23 that accommodates these is an inert gas atmosphere.

FIG. 2 shows an apparatus for carrying out the soldering method according to the second aspect of the present invention. A flux applicator 24 for applying a weak flux to the printed circuit board 16 is provided on the upper side of the soldering machine 11 of FIG. They are connected in series, and other configurations are shown in Figure 1.
Is the same as. The flux applicator 24 includes a carrier 24a for the printed circuit board 16 and the flux atomizer 2
The housing 26 has a built-in housing 5.
Explaining the properties of the weak flux described above, rosin (solid content) is about 30 wt in the ordinary flux.
% Is included. If the amount of rosin is about 10 wt%, the flux becomes weak, but if it is about this range, a cleaning means for removing the residue is required. The content of rosin is about 2 wt% in order to perform no cleaning as in the present invention.

[0012]

Description of the Embodiments An embodiment of the method of the present invention using the printed circuit board soldering apparatus shown in FIG. 1 constructed as described above will be explained. The printed circuit board 16 is supported by the carrier 11a of the soldering machine 11. Is introduced into the housing 17 in an inert gas atmosphere, preheated by the preheater 18, and then the copper foil surface of the printed board 16 is coated with solder.
The printed circuit board 16 coated with the solder is the reversing machine 12
The printed circuit board having the solder coating surface as an upper surface is transferred to the carrier 13a of the dispenser 13 and the adhesive is attached to a required portion of the printed circuit board 16 with the carrier 13a temporarily stopped. , In addition,
The printed circuit board 16 is transferred to the carrier 14a of the mounter 14 by the action of the carrier 13a.
It is taken in and stopped. In this stopped state, required electronic components are temporarily fixed to required places on the printed circuit board 16 via an adhesive. The printed circuit board 16 on which the electronic components are temporarily fixed in this way is transferred to the carrier 15a of the reflow furnace 15, taken into the housing 23 in an inert gas atmosphere, sufficiently preheated by the preheating unit 20, and then the heating unit. At 21, the solder is melted to bond the electronic component and the copper foil surface of the printed circuit board, and then the cooling part 22 is cooled to fix the bonding. end.

The time from the solder coating to the flow of the printed circuit board 16 into the reflow furnace 15 is about 4 to 5 minutes, and almost no oxidation is observed on the coated solder surface and the solder surface is easily remelted. However, since the reflow furnace 15 is overheated to a maximum of about 250 ° C., the solder surface is oxidized before melting, and good soldering cannot always be obtained, but heat treatment is performed in an inert gas atmosphere. Therefore, there is no oxidation, and good soldering is possible.

FIG. 2 shows an apparatus for carrying out the soldering method according to the second aspect of the present invention. To explain the soldering means by this apparatus, the printed circuit board 16 is attached to the carrier 24a of the flux applicator 24, and the housing 26 is attached. While being transported and moved, the flux atomizer 25 atomizes and attaches the weak flux. The printed circuit board 16 coated with the weak flux is the carrier 11 of the soldering machine 11.
It is delivered to a, taken into the housing 17, and sent to the reflow furnace 15 as described above. As described above, since the solder is coated in an atmosphere of an inert gas having a low oxygen concentration, a weak flux, more specifically, a flux having a rosin content of about 2 wt% can be used.

[0015]

As described above, according to the structure of the present invention, the following effects can be obtained. (A) Following solder coating in an inert gas atmosphere, continuous soldering is performed by reversing the printed circuit board, attaching an adhesive, temporarily fixing electronic components, and reflowing in an inert gas atmosphere. flux,
Alternatively, it is carried out under a weak flux application condition, and as in the prior art, troubles due to solder printing by a printed circuit board manufacturer can be solved, and in addition, a cleaning means for removing residues by using flux and removing solder balls can be provided. It can be omitted and the soldering efficiency can be improved. (B) Lead pitch for soldering is 0.3 mm to 0.15 m
Very easy reflow is possible even for electronic parts with fine pitches as narrow as m. (C) As shown in FIG. 4, by adjusting the residual oxygen concentration in the first step, the solder film thickness on the surface of the printed circuit board can be uniformly controlled, and the solder coating which can be soldered by the reflow furnace was performed. It is possible to manufacture printed circuit boards.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a soldering device.

FIG. 2 is an explanatory diagram of another example of the soldering device.

FIG. 3 is an explanatory diagram of a soldering machine.

FIG. 4 is a characteristic diagram of solder film thickness and residual oxygen concentration.

FIG. 5 is an explanatory diagram of a conventional soldering device.

[Explanation of symbols]

 11 Soldering Machine 12 Reversing Machine 13 Adhesive Coating Machine (Dispenser) 14 Electronic Component Mounting Machine (Mounter) 15 Reflow Furnace 16 Printed Circuit Board 17 Housing 18 Preheater 19 Solder Tank with Jet Nozzle 24 Flux Coating Machine

Claims (2)

[Claims] 1. A first step of coating a printed circuit board with solder in an inert gas atmosphere, a second step of half-turning the printed circuit board in an air atmosphere, and a temporary fixing of electronic parts to a required portion of the printed circuit board. The third step of applying an adhesive, the fourth step of temporarily fixing electronic components to the printed circuit board through the adhesive, and the fifth step of reflow soldering in an inert gas atmosphere are continuously performed in a series of lines. A method for soldering a printed circuit board, comprising: 2. The method for soldering a printed circuit board according to claim 1, wherein a weak flux is applied to the printed circuit board as a step before the first step.