JPH06170525A - Vapor heating furnace and heat treatment method - Google Patents

Abstract

PURPOSE:To execute heat treatments at various temps., to reduce the size of equipment and to simplify maintenance and service by evaporating plural liquids varying in b.p. and vapor sp.gr. and forming vapor layers divided above and below in an evaporation chamber. CONSTITUTION:Two kinds of liquids 2A, 2B are housed in a liquid housing section 1. The liquid 2B has the b.p. different from the b.p. of the liquid 2A and the vapor sp.gr. thereof is different from the vapor sp.gr. of the liquid 2A. The vapor temp. of the liquid 2A is a temp. at which cream solder is melted as a reflow furnace. The vapor temp. of the liquid 2B is a curing temp. of an adhesive. The vapors of the liquids 2A, 2B vary in the sp.gr. and therefore, the vapors stagnate dividedly as the upper and lower layers within the evaporation chamber 4 when these liquids are heated by a heater 3. Then, the work is heated at the temp. varying with each of the respective vapor layers. One furnace therefore can be used commonly as the reflow furnace and a curing furnace when this method is applied to the production of printed circuit boards. The method is adequate for the size reduction of the equipment and the simplification of the maintenance and service.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for a reflow furnace and a hardening furnace used for mounting parts of a printed wiring board, and a steam heating furnace capable of heat-treating a work at a plurality of different temperatures using steam, The present invention relates to a heating method using this steam heating furnace.

[0002]

2. Description of the Related Art A steam heating furnace (reflow furnace) is known in which a printed wiring board is carried in and heated by steam having a predetermined temperature when surface-mounted components are mounted by reflow soldering. For example, FIG. 6 is a conceptual diagram of a conventional steam heating furnace used as this reflow furnace.

In FIG. 6, reference numeral 1 is a liquid container, in which a liquid 2 having a predetermined boiling point is contained. An electric heater 3 is provided in the liquid container 1 to heat the liquid 2. A vapor chamber 4 is formed so as to surround the upper portion of the liquid storage portion 1. Reference numerals 5 and 6 denote a carry-in port and a carry-out port provided so as to horizontally traverse the steam chamber 4.

Reference numeral 7 denotes a conveyor, which sends the work 8 from the carry-in port 5 to the carry-out port 6. Reference numeral 9 is a cooling coil provided on the upper inner wall of the steam chamber 4, and 10 is a cooling coil provided at the carry-in port 5 and the carry-out port 6.

When a printed wiring board for reflow soldering is used as the work 8 here, it is heated to 220 to 250 ° C. in order to melt the cream solder. In this case, as the liquid 2, for example, FC-70 (trade name) manufactured by Sumitomo 3M Limited having a vapor temperature of 220 ° C. is used.

On the other hand, when mounting a surface mount component on a printed wiring board, not only the above-mentioned reflow soldering method, but also the surface mount component is bonded and fixed to the printed wiring board with an ultraviolet curing adhesive for heating and then melted. The flow soldering method of immersing in a solder bath may be used together. In this case, the temperature at which the cream solder is melted by the reflow soldering method (about 220 ° C.) and the temperature at which the UV-curable adhesive for heating is cured (usually 120 to 150 ° C.) are different. For this reason, in the past, a furnace for curing the adhesive (curing furnace) was installed separately from the reflow furnace.

[0007]

[Problems of the prior art] When the reflow furnace and the curing furnace are separately installed in this way, there is a problem in that the equipment becomes large and the maintenance thereof is troublesome.

Although it is possible to change the set temperature of the reflow furnace shown in FIG. 6 up and down, the set temperature is determined by the type of liquid 2 used in this steam heating furnace.
The set temperature cannot be changed during the heat treatment.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and one unit can perform heat treatment at different temperatures. If applied to the manufacture of printed wiring boards, a reflow furnace and a curing furnace can be used. It is a first object of the present invention to provide a steam heating furnace that can be used as a single unit and is suitable for downsizing equipment and simplifying maintenance.

A second object of the present invention is to provide a heat treatment method in which the heating furnace is used to heat different temperatures.

[0011]

According to the present invention, a first object is to provide a liquid containing portion for containing a plurality of liquids having different boiling points and vapor densities, and a heater for heating the liquids in the liquid containing portion and evaporating the liquids. ,
A vapor chamber that is formed above the liquid accommodating portion and that accommodates vapors of these liquids, and vapors of the liquids are separated and accumulated in layers in the vertical direction in accordance with the vapor specific gravity. This can be achieved by a steam heating furnace characterized by the above.

Conveyors for carrying the work into each vapor layer may be vertically arranged side by side, or one conveyor may be vertically moved in parallel. The work may be moved up and down from above so as to be carried into the vapor layer at a predetermined temperature. The second object can be achieved by putting the works in different steam layers of this heating furnace in order in time.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram of a steam heating furnace according to the present invention when it is not in operation, FIG. 2 is a conceptual diagram of its operating state, and FIG. 3 is an explanatory view of a treatment process of a printed wiring board as a work.

In FIG. 1, the difference from the conventional heating furnace described in FIG. 6 is that the liquid 2 contained in the liquid container 1 is 2
The points are the types 2A and 2B, and the point that the conveyor 7 is the upper and lower two-stage conveyors 7A and 7B. The liquid 2A is the same as the liquid 2 used in the one shown in FIG. 6, and for example, FC-70 (boiling point about 220 ° C.) manufactured by Sumitomo 3M Ltd. is used.

Liquid 2B has a boiling point different from that of liquid 2A (for example, 15
0 ° C.) and has a vapor specific gravity different from that of the liquid 2A, and for example, FC-40 manufactured by Sumitomo 3M Ltd. is used. The vapor temperature (220 ° C.) of the liquid 2A is a temperature for melting the cream solder as a reflow furnace, and the vapor temperature (150 ° C.) of the liquid 2B is a curing temperature of the adhesive.

In this heating furnace, the liquid 2A, 2B is heated by the heater 3.
When heated, since the specific gravity of the steam is different, the steam separates and stays in the steam chamber 4 as upper and lower layers 11A and 11B (FIG. 2). That is, the upper vapor layer 11A is kept at about 150 ° C and the lower vapor layer 11B is kept at 220 ° C. The cooled vapor is condensed on the inner wall of the vapor layer 4 and returns to the liquid container 1 to circulate. Further, the cooling coils 10 at the loading / unloading ports 5 and 6 capture the steam escaping to the outside and return it to the liquid storage unit 1.

The work processed in this heating furnace is the printed wiring board 8 (8A to 8D) shown in FIG. Surface mount pads 12 and 13 and through holes 14 are formed on both surfaces a and b of the wiring board 8. First, as shown in FIG. 3 (A), cream solder 15 is applied to the pad 12 on one surface a, and the lead of the component 16 is bonded thereto.

The printed wiring board 8A shown in FIG. 3 (A)
Is loaded from the carry-in port 5 to the lower conveyor 7A in FIG.
It is carried into the lower vapor layer 11A. Since the vapor layer 11A is maintained at about 220 ° C., the cream solder 15 is melted and reflow soldering is performed. Then, the wiring board 8B shown in FIG. In this figure, reference numeral 17 shows a soldering portion with the cream solder 15.

The wiring board 8B is turned upside down as shown in FIG. 3C, and the adhesive 18 is applied to the component mounting portion on the surface b. A component 19 is further placed on this wiring board 8C,
It is adhered to the adhesive 18 as shown in FIG. The wiring board 8D is placed on the conveyor 7B in the upper stage of the heating furnace from the carry-in port 5 and put in the upper vapor layer 11B. This vapor layer 1
Since 1B has a temperature of about 150 ° C., only the adhesive 18 is thermoset without melting the soldering portion 17 due to reflow.
In FIG. 3 (E), 18 'shows the cured adhesive 18. The wiring board 8D '(see FIG. 2) in which the adhesive 18 has hardened is the unloading port 6
Be shipped from.

The wiring board 8D 'is turned upside down again, and the leads of the leaded component 20 are inserted into the through holes 14. A jet 21 of molten solder is applied to the lower surface (surface b) of this wiring board 8E (8D ') for flow soldering. As a result, the component 19 is soldered to the pad 13 and the lead of the component 20 is soldered to the through hole 14, respectively.
The mounted printed wiring board 8F shown in (F) is obtained.

The heating furnace of the mounting example shown in FIGS.
Since the conveyors 7A and 7B are separately provided for the vapor layers 11A and 11B, respectively, different works can be simultaneously processed at different temperatures, and the processing efficiency is increased.

FIG. 4 is a conceptual diagram of the second embodiment. In the embodiment, the conveyors 7A and 7B of the embodiments of FIGS. 1 and 2 are replaced with a single conveyor 7C that can move up and down. That is, if the conveyor 7C is in the lower stage, the work 8 can be put in the lower vapor layer 11A, and if it is in the upper stage, the work 8 can be put in the upper vapor layer 11B.

FIG. 5 is a conceptual diagram of the third embodiment. This embodiment has a conveying means 7D for moving the work 8 up and down. According to this embodiment, the work 8 is attached to the upper and lower vapor layers 11
The work 8 can be carried in to the appropriate positions of B and 11A, and the work 8 can be carried out by causing the work 8 to stay in the predetermined vapor layer for a predetermined time and then the conveying means 7D to be fed back. In FIGS. 4 and 5, parts corresponding to those in FIGS.

In each of the above-described embodiments, the upper and lower parts 2 are placed in the steam chamber 4.
Although the two vapor layers 11A and 11B are formed, three or more types of liquids may be contained in the liquid container 1 so that the vapors thereof are separated and retained in three or more layers. The heating furnace of the present invention is suitable for use as a reflow furnace and a hardening furnace for printed wiring boards, but is not limited to this.

[0025]

As described above, according to the invention of claim 1, since a plurality of liquids having different boiling points and vapor specific gravities are vaporized to form vapor layers which are vertically separated in the vaporization chamber, The work can be heated to different temperatures for each layer. Therefore, it is not necessary to prepare a plurality of heating furnaces, the equipment can be downsized, and maintenance can be facilitated.

The loading and unloading of the work may be performed by a conveyor provided for each vapor layer (claim 2), or the conveyor may be moved up and down (claim 3). The work may be moved up and down.

If this heating furnace is used for heating a work requiring heat treatment at a plurality of temperatures, the work conveying distance can be shortened and efficiency can be further improved (claim 4). In this case, if the heating furnace of the present invention is applied to the reflow furnace and the curing furnace used when mounting the surface mount components on the printed wiring board, one heating furnace is sufficient and the present invention can be effectively used. (Claim 5).

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an embodiment of the present invention when not in operation.

[Fig. 2] Similarly, a conceptual diagram during operation

FIG. 3 is a diagram showing a component mounting process of a printed wiring board as a work.

FIG. 4 is a conceptual diagram of another embodiment.

FIG. 5 is a conceptual diagram of another embodiment.

FIG. 6 is a conceptual diagram of a conventional device.

[Explanation of symbols]

 1 Liquid Storage Section 2, 2A, 2B Liquid 3 Heater 4 Steam Chamber 7A, 7B, 7C, 7D Conveyor 8, 8A-8F Printed Wiring Board as Workpiece 15 Cream Solder 18 Adhesive

Claims (5)

[Claims] 1. A liquid storage part for storing a plurality of liquids having different boiling points and vapor specific gravities, a heater for heating the liquids in the liquid storage part to evaporate the liquids, and a heater formed above the liquid storage part. And a vapor chamber for accommodating the vapor of the liquid, wherein the vapors of the liquids are vertically separated and accumulated in the vapor chamber in a vertical direction in accordance with the specific gravity of the vapor. 2. The steam heating furnace according to claim 1, wherein the steam chamber is provided with a conveyor for laterally transporting the work in a steam layer of the same liquid for each steam layer. 3. The steam heating furnace according to claim 1, wherein the steam chamber is provided with a conveyor for laterally moving the work so as to be vertically movable. 4. The workpieces which need to be heat-treated a plurality of times at different temperatures are put into the vapor chambers of the steam heating furnace according to any one of claims 1 to 3 in the vapors of different liquids which are separately retained vertically. A heat treatment method, which comprises heating by heating. 5. The heat treatment method according to claim 4, wherein the work is a printed wiring board having surface mount components fixed with cream solder and surface mount components fixed with an adhesive and subjected to flow soldering.