Amount of copper within the PCB Number of surface mount components Type of surface mount components In order to create a reflow profile thermocouples are connected to a sample assembly usually with high temperature solder in a number of locations to measure the range of temperatures across the PCB. It is recommended to have at least one thermocouple located on a pad towards the edge of the PCB and one thermocouple located on a pad towards the middle of the PCB. Within a typical reflow soldering profile there are usually four stages — Preheat, soak, reflow and cooling. The main aim being to transfer enough heat into the assembly to melt the solder and form the solder joints without causing any damage to components or PCB.
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.
Numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB. 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.
With infrared reflow, the board designer must lay the board out so that short components don't fall into the shadows of tall components. 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.
However, most electronic assemblies are made using a "No-Clean" process where the flux residues are designed to be left on the circuit board, since they are considered harmless.
This saves the cost of cleaning, speeds up the manufacturing process, and reduces waste. Another reason to remove no-clean residues is to improve adhesion of conformal coatings and underfill materials.
Proper cleaning removes all traces of solder flux, as well as dirt and other contaminants that may be invisible to the naked eye. No-Clean or other soldering processes may leave "white residues" that, according to IPC, are acceptable "provided that these residues have been qualified and documented as benign".
Additionally, in some applications, such as low-end electronics, such stringent manufacturing methods are excessive both in expense and time required. Finally, the boards are visually inspected for missing or misaligned components and solder bridging. If needed, they are sent to a rework station where a human operator repairs any errors.
This technology has proven highly efficient for process improvements and quality achievements. As of [update] smallest component is metric measuring 0.SMT Reflow Soldering Technology. Founded in , Heller Industries, pioneered convection reflow soldering in the s.
Over the years, Heller has worked in partnership with our customers to continually refine the systems to satisfy advanced application requirements.
Inline SMT Reflow Soldering Ovens Conveyorized solder reflow ovens for SMT assembly offer space-saving design without skimping on capability.
Each SMT reflow oven uses full-convection reflow soldering for high-quality, reliable results. 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. FM-SMT Electronics Co., Ltd. is best SMT Reflow Soldering, Lead Free Reflow Soldering and Reflow Soldering Machine supplier, we has good quality products & service from China.
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 . 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.