Fluxing: the critical parameter in wave soldering.
Fluxing is a critical parameter in the wave soldering Applying liquid solder to the underside of printed circuit boards in order to bond the chips and discrete components that are placed on top of the board and whose metal leads (pins) extend through the board. process, and with the introduction of Pb-free soldering, flux can determine whether the process is sucessful. There is more to consider than just the choice of fluxes; success also depends on how the flux is applied, and the accuracy of that application method.
Flux is involved in wave soldering in a number of areas, and quite a few issues arise relative to the qualification, handling, application and processing of flux:
* Before soldering begins, verify that the flux is not past its expiration date Expiration Date
The day on which an options or futures contract is no longer valid and, therefore, ceases to exist.
The expiration date for all listed stock options in the U.S. , and that it has been stored correctly. Respect the storage guidelines on the flux datasheet and be sure that water-based fluxes have not been frozen during shipping.
* For flux applications with a pump system, use the container provided by the flux supplier. In the case of a pressurized pres·sur·ize
tr.v. pres·sur·ized, pres·sur·iz·ing, pres·sur·iz·es
1. To maintain normal air pressure in (an enclosure, as an aircraft or submarine).
2. vessel where the flux must be poured into the vessel, take appropriate safety precautions and handle the flux away from the production environment.
* When applied on the solder side of the assembly, flux should wet to nonmetallic non·me·tal·lic
1. Not metallic.
2. Chemistry Of, relating to, or being a nonmetal.
Adj. 1. surfaces. It should be compatible with the solder resist (Figure 1).
* Flux should be preheated according to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. the specified topside board temperature, which can usually be found in the flux datasheet.
* Flux must remove oxides that have been formed on the copper pads, components and other metallic surfaces.
* During soldering, the flux should support the solder and prevent bridging when the board exits the molten solder.
* Flux residues should be harmless and meet Bellcore and IPC (1) (InterProcess Communication) The exchange of data between one program and another either within the same computer or over a network. It implies a protocol that guarantees a response to a request. SIR requirements, and Bellcore electromi-gration standards.
* For the sake of machine maintenance, it is helpful if the flux can be removed easily.
Application methods. Flux application is a technology in itself. Different techniques are available; e.g., foam, wave, drum, spray fluxing. For today's flux chemistries, spray fluxing using atomizing air nozzles is preferred. Its advantageous characteristics include uniform deposition; ease in controlling the amount of flux; and, because it is a closed system, no drift in flux density flux density
The rate of flow of fluid, particles, or energy per unit area. .
Spray fluxing forces flux in a vertical direction using atomizing air to create small droplets and to form a good interaction with the surface and penetration into the copper barrels.
The flux can be supplied by a pressurized tank system or a pump. For applications in which a gear pump A Gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps however are also widely used in chemical installations to pump fluid with a certain viscosity. is used, compatibility with some milky VOC-free water-based fluxes must be verified.
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In most applications, the nozzle will be mounted on a transferring device. The speed of the nozzle movement should be adjustable as it needs to change when conveyor speed changes. The amount of flux can be varied by pump frequency or tank pressure. In addition, dedicated machines can spray specific areas of the assembly--very useful for boards mounted in pallets.
After spraying, the remaining flux should be removed from the nozzle head, otherwise the solvent will evaporate and crystals that are left behind will accumulate and cause clogging. One method of removal is to use a shot of pressurized air. The flux will be blown out of the nozzle head by venturi venturi
a tube with a decrease in the inside diameter that is used to increase the flow velocity of the fluid and thereby cause a pressure drop; used to measure the flow velocity (a venturimeter) or to draw another fluid into the stream. forces.
Flux characteristics. A good flux is active when the assembly leaves the liquidous solder, and acts to prevent bridging when solder drains away from soldered joints. For a double wave concept, it is important that not all the flux is washed off on the first wave-former.
The flux must provide good solderability. After soldering, it should leave a residue that is cosmetically acceptable and makes pin testing possible. A correctly set up solder wave will adequately adequately flush remaining flux residues. Regarding the process, the flux should leave no solder balls, but it should support through-hole penetration and prevent bridging.
Pb-free conversions, VOC (Vertical Online Community) See vertical portal. legislation and taxes in different areas of the world are driving assemblers This is a list of assemblers. Hundreds of assemblers have been written; some notable examples are:
Not flammable, especially not readily ignited and not rapidly burned. and have a shelf life of approximately 18 months. Freezing should be prevented during storage.
Gerjan Diepstraten is a senior process engineer with Vitronics Soltec BV (vitronics-soltec.com); firstname.lastname@example.org. His column appears monthly.