Wave soldering

Wave soldering or wave soldering is a soldering method, with the electronic modules (circuit boards, printed circuit boards ) are soldered semi or fully automatically after loading.

  • 4.1 Selective Soldering
  • 4.2 Repair soldering

Method

Fluxing

The solder side of the PCB is first wetted in Fluxer with a flux. This can be applied by spraying ( Sprayfluxen ) or foaming ( foam fluxing ) happen. Allow a finer spray fluxing dosage by setting the flow rate in ml / min. Sprühfluxern at the area of ​​the flux of order in the x- and y-direction can be specified by start and end points.

A suction prevents a flow vapor exiting the Fluxer.

Preheat

Thereafter, the board by convection ( turbulence of heat, thereby practically anywhere, even on the top, the same temperature applied ) preheated filament heating or infrared emitters. This happens for one to evaporate the solvent portion of the flux (otherwise blistering during the soldering process ) to avoid to increase the chemical action of activators and to a temperature delay the assembly as well as damage to the components by too steep a rise in temperature during the subsequent soldering. Usually a temperature difference of less than 120 ° C is required. This means that at a brazing temperature of 250 ° C, the board must have been heated to at least 130 ° C.

Accurate data resulting from temperature profiles. This temperature sensor can be mounted at relevant points and recorded with a measuring device on a sample board. Temperature curves are obtained for the platinum top and bottom, and selected components.

Soldering

Now the module is run over one or two solder waves. The solder wave is generated by the pumping of liquid solder through an opening. In the chip wave through a gap in the Wörthmann shaft through the holes of a perforated plate, otherwise through the slotted holes of a perforated plate.

Double wave systems (chip - and delta wave ) have been replaced almost entirely by the Wörthmann wave (single shaft system ).

Benefits of Wörthmann wave:

  • Complete wetting of SMD pads
  • Little error in the wetting by shadow effects
  • Good soldering of difficult cases (SOT 23)
  • Less solder bridges with SMD pads

Advantages of a single wave:

  • No double temperature stress
  • Avoiding the dry soldering the assembly by worn flux

Parameter

The reflow temperature is leaded solder at 250 ° C for lead- free solder is about 10 ° C to 30 ° C higher, ie at 260 ° C to 280 ° C.

Background: Mainly in the mixed assembly of a plant operating with 260 ° C, since there are still a lot of components that absorb only 260 ° C according to the datasheet. Also requested by some customers is the service provider the maximum soldering temperature of 260 ° C or issued only for a release. From 260 ° C the Ablegierung increases disproportionately. Disadvantage then is the relatively small process window.

The soldering time must be chosen so that the warming will not harm the board nor the heat-sensitive components. The soldering is the contact time of the liquid solder per solder joint. The reference times are not more than two seconds for single-sided printed circuit board is less than one second, and in double-faced circuit board. For multi- circuit boards custom soldering times, about two to three seconds for the 3 -hole Wörthmann wave and four to six seconds for 5-hole Wörthmann shaft apply. According to DIN EN 61760-1: 1998, the maximum time for one or two waves together is 10 seconds.

The immersion depth of the circuit board is set so that a wash over the same of the shaft is not possible.

The pulling angle is between 5 to 10 °, 7 ° is used most frequently (some soldering systems have a non-adjustable soldering angle of 7 °). The slope of the transport path for solder wave is determined by the course of the rows of pins of the components. With predominantly in the longitudinal direction to the surge - so fluidly low wires running - is the pulling angle to choose flatter than predominantly transverse rows of pins. For larger areas contiguous copper (shield areas) on the solder side is to go flat because otherwise the solder to flow freely to the areas on the circuit board from the solder pot along the wave soldering. The adjustment of the pulling angle also determines the solder thickness on the solder joints. The flatter the pulling angle, the more solder remains on the soldering joints. The risk of droplet and bridge formation rises. The steeper the pulling angle, the more economical is the Lotablagerung.

The shape of the shaft depends on the application and the final critical. Nowadays, common waveforms are chip -, lambda - and Wörthmann waves. Usually two waves (chip - and delta wave ) used directly behind each other to be more complex Lötsituationen justice. So SMD components can be soldered on the PCB back and THT components on the PCB top side in the same operation safely on the board. For PCBs, only with THT components, only the delta wave is usually required. With the Wörthmann wave SMD and THT components can be soldered simultaneously.

Cooling

After soldering, a cooling of the assembly is useful in order to reduce the thermal load quickly. This is done through a direct cooling by a cooling unit (air conditioning ), immediately after the soldering area and / or a conventional fan in the lowering station, or a cooling tunnel in the return band.

Application

The wave soldering is mainly used in soldering of printed circuit boards, which are equipped partly or solely with THT components. Of importance wave soldering is also in the assembly of SMD components on the bottom side. In the course of miniaturization of components, the wave soldering has been replaced in recent years in many cases by the reflow soldering, with the SMD components can be economically assemble.

In the area of ​​power electronics, in the often very massive or large components must be soldered, wave soldering is often the only economically usable soldering techniques.

The wave soldering is compared with a larger number of components or solder joints with the selective soldering usually more economical, since the wave soldering in practice usually requires less time.

Protective gas

Today, the wave soldering takes place usually in an inert gas atmosphere. With the use of nitrogen, the adverse influence of oxygen is avoided in the soldering process. In practical use can be achieved with tunnels residual oxygen is of the order of about 100 ppm.

The nitrogen application provides the ability to reduce costs and make the process safer. In particular, rework and repair of solder joints can be avoided.

Further benefits from the use of nitrogen as process gas are:

  • Improved solder joints by higher wetting speeds.
  • Substantially reduced solder consumption by reducing the tin-lead oxides ( scabies).
  • Reduced flux consumption, mild -activated flux.
  • Cleanliness of PCBs
  • Reduced maintenance
  • Eco-friendly soldering
  • Possibility of using lead-free solders

The nitrogen is blown into the solder area and held by the precise adjustment of the suction ( at the beginning and end of the machine ) in this area. As a good residual oxygen content values ​​are from about 25 to 50 ppm. Less than 25 ppm in the formation of Zinnperlen throughout the soldering area, from 100 ppm ( lead-free) slag is formed in and around the solder nozzles, with leaded tin until 200 ppm. Thus, the soldering quality is not compromised, the slag must be removed at regular intervals in cleaning the system. Without the use of nitrogen, there is an extremely strong formation of slag on the solder pot.

Variations

Selective Soldering

An ever more increasingly important variant of the wave soldering provides the selective wave soldering dar. this is not the whole assembly, but only a small part of it soldered by means of a " miniature wave". The effective range can be soldered here, depending on the Lötdüsenform be only a few square millimeters in size. The assembly is placed precisely for this purpose with a positioning on the wave. For this purpose, each component to be soldered must be entered with the exact values ​​of x and y axis in the soldering program (eg a male connector with 10 pins, the starting coordinate of the first pins and the end coordinate of the last pins). The clip frame or the ticking with the / the module (s ) is first driven and heated above the Vorheizungsfeld. The flux application is usually done by one or two very small spray nozzles, where just to be soldered pins / pin rows are sprayed. When soldering the same path is processed as in the fluxing, pin for pin for each component. Individual pins through individual approach, called point soldering. Several pins (plug, pin strips ) by lowering the first pins and drive a car up shortly after the last pin. Fits only one module in the framework is worked with a fluxing and soldering nozzle. Fit two or multiples of two in the frame, you can work with two fluxing and soldering nozzles. In selective soldering it is also easily possible to use next to a pot with leaded tin a second with lead free pewter. When changing a product between the crucibles in the soldering program only the offset or position of the second crucible must be entered. The selective soldering applies if a lot of SMD components have been soldered in a reflow process on a circuit board and a few THT components must be soldered. A second thermal stress on the circuit board and the components thereon can be avoided. Another field of application is the soldering of components on the solder side, after flow soldering.

Selective soldering after Hub-/Tauchverfahren is a variant in which a product-specific multi-nozzle - soldering tool is used, then all the designated parts to be soldered at the same time, by the circuit board is lowered onto the nozzles arranged. Here several miniature waves form a multi-wavelength system.

The selective soldering is often the only possible soldering if both sides wired components must be soldered and a wave soldering process with the classic waves on the second page of the module is no longer possible. Compared with the classical wave soldering Selective soldering takes the usually much less space. The Selektivlöttechnologie is particularly economical when few components or very few pins must be soldered.

Repair soldering

Reparaturlötanlagen have a miniature wave ( depending on the type of wave of about 3 cm × 10 cm to 10 cm × 25 cm). If it is determined after wave soldering, components that do not lie on the board or have been soldered upside down, must be reworked. Typical applications include components not or can only be replaced at considerable expense with many pins (plug, pin headers, ...) or components which have a high heat capacity and other Reparaturlötverfahren. When repair soldering flux is in the affected area of ​​the module applied and, where the assembly into the liquid solder the Reparaturschwallbads. The heat input of the rivers solder melts the solder the components on the circuit board so that the affected component can be either aligned or withdrawn. When replacing a component, a new component is placed in the printed circuit board immediately. The molten solder makes the solder joint between the component and the circuit board.

Shielding gas
530566
de