GB2418881A

GB2418881A - Wave soldering apparatus

Info

Publication number: GB2418881A
Application number: GB0422002A
Authority: GB
Inventors: Willemen Lambertus Christiaan
Original assignee: Vitronics Soltec BV
Current assignee: Vitronics Soltec BV
Priority date: 2003-10-07
Filing date: 2004-10-05
Publication date: 2006-04-12
Anticipated expiration: 2024-10-05
Also published as: NL1024476C2; GB2418881B; GB0422186D0; GB0422002D0

Abstract

A wave soldering apparatus includes a blowing device 12 for blowing inert gas 18 towards the solder wave 7 so as to ensure that it overflows out of the nozzle 4 in the correct direction, i.e. in a direction opposite to the direction of travel of the printed circuit board 6 being soldered. The wave soldering apparatus also comprises a solder bath 1, and a pump 3 for pumping solder 2 through the nozzle 4. Preferably one or more sides of the nozzle 4 is/are made of a wettable material 5, with the other side(s) being made of a non-wettable material, further ensuring that the solder wave 7 flows along the wettable material 5 in the correct direction. A wettable guiding strip (14, figure 4) may be mounted next to the nozzle 4 to perform the same function. The supply of inert gas 18 is preferably able to be switched on and off quickly, and a heating element (11, figure 2) is preferably used to heat the inert gas 18 to prevent forced cooling of the solder wave 7.

Description

1 241 8881 Apparatus for selective soldering.

This invention relates to an apparatus for soldering on printed circuit boards of through hole components, containing leads.

More and more surface mount components are used for printed circuit assemblies, characterized by small dimensions and soldered by a reflow soldering process.

Many of the circuit assemblies contain however components that are not suitable for reflow soldering. This concerns in general components like connectors and electrolytic capacitors, which have through hole leads that need to be mounted onto printed circuit boards and soldered on the other side of the print. The solder has to be applied at the bottom, the solder side, of the printed circuit board.

A soldering apparatus is known which contains: - a solder pot to store and heat the molten solder; - a transport device to move the assembly to be soldered over the nozzle and carry off the soldered assembly; - at least one vertical mounted nozzle in the solder pot; through which the molten solder flows and overflows over the nozzle plate back into the described solder pot; - a pump device to supply the molten solder at the bottom of the nozzle; and a transport device for at least bring together the bottom side of the assembly to be soldered and the top side of the nozzle.

In this manner the nozzle forms a small soldering apparatus. Herewith it is possible to solder by moving the assembly just over the solder wave. The solder will penetrate into the barrels along the leads of the through hole components at the bottom side of the printed circuit assembly.

It is already known that a soldering apparatus with a nozzle has one disadvantage, that is the solder does not always flow in the proper direction, the opposite direction of the dragged printed assembly.

The result of the total forces leads to unstable flow behaviour of the molten solder. Resulting in bridging between one or more leads. This includes also, that during the design of the printed circuit assembly space must be created for the flowing solder; on those areas no components are allowed.

It is already known that the shape of the vertical nozzle forces the molten solder to flow to one direction, but this does not always gives the required result.

The present innovation has for its aim 'o produce a soldering apparatus with which the molten solder always flows in a defined direction, that is the opposite direction of the transported printed circuit assembly.

By experiences it is known, that stable flows of the molten solder in one define direction prevents bridging and damaging of the surrounded surface mount devices.

In the first presented invention an inert gas is blown towards the solder, in such way that the solder is forced to flow in the proper direction.

According to a further development of the apparatus, the gas supply can be switched on and off quickly to optimise the blowing without effecting the soldering process.

To achieve a proper solder temperature it is required to adjust the gas temperature.

According to a further development of the apparatus, the invention proposes a vertical nozzle including a wettable flow plate at the overflow side of the molten solder, where as the other sides of the nozzle are made out of non-wettable materials.

The non-wettable part of the nozzle will reject solder and solder will flow along the wettable part that attracts the molten solder.

In a particular embodiment a metal strip is mounted along the vertical nozzle. This strip is made out of wettable material and will attract molten solder. Instead of a strip, it is also possible to have another shaped wettable material, like a rod.

DE19807696 describes an apparatus for soldering supplying a gas surround a vertical mounted nozzle through which molten solder flows. In this device the heated gas is used to have an inert atmosphere in the soldering area.

The solder is overflowing in all directions of the nozzle, which requires more free space on the painted assembly to prevent damaging of surface mount components.

The examples, which follow, explain the invention: Figure 1 is a schematic overview according the innovation; Figure 2 is a schematic overview of a device for the supply of an inert gas including a device that offers the ability to fast switch on and off the supply of gas; Figure 3 is a detailed view of the vertical nozzle with wettable overflow plate; Figure 4 a detailed view of a vertical nozzle with a wettable metal strip.

Figure 1 shows a solder pot (1) that is filled with molten solder (7). For the melting and keeping the solder liquidus the heating elements are used that are known in today's technology, which are not drawn in figure (1).

In the solder pot (1) is a vertical nozzle (4) is mounted. By means of a pump (3) the solder is pumped from the solder pot (1) through the vertical nozzle (4).

The molten solder (7) will flow out of the vertical nozzle back into the solder pot (1). To make a solder connection the printed circuit assembly (6) is moved by means of a transport device (8) of which only the grippers are drawn, to a short distance of the vertical nozzle (4).

Next the printed circuit assembly (6) is dragged over the vertical nozzle (4), which makes the overflowing molten solder (7) connecting the leads (9) of the components (10) to the bottom side of the printed circuit assembly (6).

To make the molten solder (7) flow over the slope surface (5) of the vertical nozzle (4) a inert gas, for example nitrogen, is blown out of a blowing device (12) in the direction of the overflowing opening (19) of the vertical nozzle (4).

The inert gas (18) flows via the blowing device (12) against the flowing molten solder (7) into the direction of the slope surface (5).

The solder will select the direction of the lowest resistance and flow over the slope surface (5) back into the solder pot (1).

Figure 2 illustrates a device to quick switch on and off of the supplied inert gas (18). This may be necessary to prevent the molten solder (7) to be blown through the holes of the printed circuit assembly (6). The device contains a heating element (11) through which the inert gas (18) is blown. Heating of the inert gas (18) is necessary to prevent a forced cooling of the liquidus solder.

A distribution valve (15) is open, through which the supplied inert gas (18) is blown into the free space.

During the soldering this distribution valve (15) will be closed. This will blow the inert gas (18) through the blowing device (12) against the molten solder (7). A cylinder (17) makes the distribution valve (15) quickly open and close allowing the inert gas (18) fast changing between blowing against the molten solder (7) and into the free space. This prevents the molten solder to be blown on top of the printed circuit assembly (6).

Figure 3 shows another design that forces the solder to flow into the proper direction. This innovation uses wettable and non-wettable materials. The characteristic of a wettable material is that it attracts the molten solder (7) where as the non-wettable material the molten solder (7) rejects. The solder that flows out of the vertical nozzle (4) is attracted by the slope surface (5), made out of wettable material. The other part of the vertical nozzle (4) is made out of a non-wettable material, like stainless steel, and will reject the solder.

Figure 4 shows another design of a vertical nozzle (4) made out of nonwettable materials with a guiding strip (14). The guiding strip (14) is made out of wettable material and will attract the flowing molten solder (7).

Claims

CLAIMS: 1. A soldering apparatus containing: - a solder pot (1) for

storage and heating of the molten solder (7); - a transport device (8) to drag and carry off the circuit assembly over the solder pot!1); - at least one vertical nozzle (4) mounted in the solder pot (1); through which the molten solder (7) is pumped overflowing through the nozzle opening (19) back into the described solder pot (1); - a pump (3) to supply molten solder (7)through the bottom of the vertical nozzle (4); and a transport device (8) to bring together the bottom side of the printed circuit assembly (6) and tr.e top side of the vertical nozzle (4), characterized in that an inert gas (18) is blown through the blowing device (12) that makes the molten solder (7) overflowing through the nozzle opening (19) in the correct direction.
2. A soldering apparatus as claimed in Claim 1, characterized that one or more sides of the vertical nozzle (4) is made of a wettable material (5) and the others of a non-wettable material (4), which will make the solder flow along the wettable material (5) in the correct direction.
3. A soldering apparatus as claimed in Claim 1 an/or 2, characterized that next to the vertical mounted nozzle (4) a wettable guiding strip (14) is mounted, which makes the molten solder (7) flow through the nozzle opening (19) along the wettable guiding strip (14).
4. A soldering apparatus as claimed in Claim 1, characterized that the supply of the inert gas (18) can be switched on and off quickly. The apparatus contains a heating element (11) through which an inert gas (18) is blown.

An open distribution valve (15) makes the supplied inert gas (18) through the exhaust tube (16) flow into the free space. During soldering the distribution valve (15) will be closed. This makes the inert gas (18) flow through the blowing device (12) against the molten solder (7).

A cylinder (17) makes the distribution valve (15) open and close fast, which makes it possible to switch fast between blowing the inert gas (18) against the molten solder (7) or into the free space.
5. A soldering apparatus as claimed in Claim 4, I' characterized in that the temperature of the inert gas . (18), that flows out of the blowing device (12), is controlled to prevent forced cooling of the molten solder (7) by guiding through the heating element (11) and ë I: heated to the desired temperature before blown through the blowing device (12).

5. A soldering apparatus as claimed in Claim 1, characterized that the temperature of the inert gas (18), that flows out of the blowing device (12), is controlled to prevent forced cooling of the molten solder (7).

Therefore the inert gas (18) is guided through a heating element (11) and heated to the desired temperature before blown through the blowing device (12).

Amendments to the claims have been filed as follows 1.A soldering apparatus containing: - a solder pot (1) for storage and heating of molten solder (7); - a transport device (8) to drag and carry off a printed circuit assembly over the solder pot (1); - at least one vertical nozzle (4) mounted in the solder pot (1); through which the molten solder (7) is pumped overflowing through a nozzle opening (19) back into the described solder pot (1); - a pump (3) to supply molten solder (7)through a bottom of the vertical nozzle (4); the transport device (8) bringing together a bottom side of the printed circuit assembly (6) and the nozzle opening of the vertical nozzle (4), characterized in that an inert gas (18) is blown through a blowing device (12)

-

^'. so that the molten solder (7) overflows through the ^-, nozzle opening (19) in the correct direction. .

2.A soldering apparatus as claimed in Claim 1, .

characterized in that one or more sides of the vertical nozzle (4) is made of a wettable material (5) and the others of a non-wettable material (4), which will make the solder flow along the wettable material (5) in the correct direction.

3.A soldering apparatus as claimed in Claim 1 and/or 2, characterized in that next to the vertical nozzle (4) a wettable guiding strip (14) is mounted, which makes the molten solder (7) flow through the nozzle opening (19) along the wettable guiding strip (14).

4. A soldering apparatus as claimed in Claim 1, containing - a supply of the inert gas (18) that can be switched on and off quickly; - a heating element (11) through which the inert gas (18) is blown; - an open distribution valve (15) making the supplied inert gas (18) flow through an exhaust tube (16) into a free space, while during soldering the distribution valve (15) will be closed resulting in the inert gas (18) flowing through the blowing device (12) against the molten solder (7); - a cylinder (17) making the distribution valve (15) open and close fast, which makes it possible to switch fast between blowing the inert gas (18) against the molten solder (7) or into the free space. .