Preheat zone[ edit ] Preheat is the first stage of the reflow process.
Assembly line with SMT placement equipment Where components are to be placed, the printed circuit board normally has flat, usually tin -lead, silver, or gold plated copper pads without holes, called solder pads. Solder pastea sticky mixture of flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a screen printing process.
It can also be applied by a jet-printing mechanism, similar to an inkjet printer. After pasting, the boards then proceed to the pick-and-place machineswhere they are placed on a conveyor belt. Some large integrated circuits are delivered in static-free trays.
technology (SMT) and focuses on the SMT component-to-board reflow soldering process and rework soldering if you are removing or replacing individual components on already-assembled boards. 1 The information in this application note is for your reference only. Reflow soldering, like wave soldering, is not a new manufacturing process. The hybrid industry has used and refined the art of reflow soldering for many years. However, with the advent of Surface Mount Technology (SMT), reflow soldering has expanded in the number of types and has been studied, refined and explored as never before. Reflow soldering is the most common method of attaching surface mount components to a circuit board, although it can also be used for through-hole components by filling the holes with solder paste and inserting the component leads through the paste.
Numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the Smt reflow soldering. They first enter a pre-heat zone, where the temperature of the board and all the components is gradually, uniformly raised.
The boards then enter a zone where the temperature is high enough to melt the solder particles in the solder paste, bonding the component leads to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed, surface tension automatically aligns the components on their pads.
There are a number of techniques for reflowing solder. One is to use infrared lamps; this is called infrared reflow.
Another is to use a hot gas convection. Another technology which is becoming popular again is special fluorocarbon liquids with high boiling points which use a method called vapor phase reflow.
Due to environmental concerns, this method was falling out of favor until lead-free legislation was introduced which requires tighter controls on soldering.
At the end ofconvection soldering was the most popular reflow technology using either standard air or nitrogen gas. Each method has its advantages and disadvantages.
Component location is less restricted if the designer knows that vapor phase reflow or convection soldering will be used in production. Following reflow soldering, certain irregular or heat-sensitive components may be installed and soldered by hand, or in large-scale automation, by focused infrared beam FIB or localized convection equipment.
If the circuit board is double-sided then this printing, placement, reflow process may be repeated using either solder paste or glue to hold the components in place.
If a wave soldering process is used, then the parts must be glued to the board prior to processing to prevent them from floating off when the solder paste holding them in place is melted.
After soldering, the boards may be washed to remove flux residues and any stray solder balls that could short out closely spaced component leads. Rosin flux is removed with fluorocarbon solvents, high flash point hydrocarbon solvents, or low flash solvents e. Water-soluble fluxes are removed with deionized water and detergent, followed by an air blast to quickly remove residual water.Reflow soldering techniques are used for surface-mount parts.
Whilst most surface-mount boards can be assembled manually using a soldering iron and solder wire, the process is slow and the resultant boards can be unreliable. Nov 16, · Juki Automation Systems is now offering a complete line of lead-free hot-air reflow ovens from JT Automation Equipment, LTD.
Distributed with the . For SMT reflow soldering means: In SMT reflow systems the heat tranfer takes place by full convection. Heated process gas (air, nitrogen) is guided on the products by nozzle plates. The resulting temperature profile has to be conform with guidelines of component and solder paste manufacturer.
Reflow soldering is the most widely used method of attaching surface mount components to printed circuit boards (PCBs). The aim of the process is to form acceptable solder joints by first pre-heating the components/PCB/solder paste and then melting the solder without causing damage by overheating.
Surface-mount technology (SMT) Following reflow soldering, certain irregular or heat-sensitive components may be installed and soldered by hand, or in large-scale automation, by focused infrared beam (FIB) or localized convection equipment.
SMT reflow systems distinguish oneself by long life cycle and high process stability. Innovative developments as process gas cleaning system "ABS" ensure high system standing times.