In a hot reflow oven, solder is thermally processed for use in the production of electronic components. For extremely tiny lab-size operations, a led reflow burner can use as a small packet or box-type oven. A conveyor or inline belt reflow furnace is the best option for larger enterprises.
The infrared or IR heating technique is going to use throughout the early stages of electronics production. Subsequently, the market shifted to convection thermal transmission, pioneered by businesses such as BTU International. One of the numerous benefits of convection hot reflow ovens was the significant improvement in thermal uniformity. Closed-loop convection uses in the most recent reflow ovens.
How Does Solder Reflow Oven Configure?
The configuration of inline hot reflow ovens consists of a variety of heating sections and a cooling portion. There must be a few zones—eight or fewer—or many zones—twelve or more—based on the size, throughput, and length of the reflow oven. The areas configure with a heat transfer set point that will use throughout the reflow soldering procedure. The PCB must expose to this very set point’s temperature when it travels through that area.
The software called “the recipe” contains all of the region temperatures and the speed of the belt. “The profile” signifies the temperature that the circuit “sees” as it passes through the reflow oven.
The software recipe is customized to produce the solder paste profile that the maker of the soldering reflow machine has defined for the circuit. The soldering reflow oven’s maximum and lowest peak temperatures, as well as employ other characteristics like Flux Duration (FAT), Time Over Liquids (TAL), and cooling and heating ramp rates.
PCBs process in a reflow oven in air, in a supervised forming gas or nitrogen environment, or both. Forming gas or nitrogen uses to lessen or completely prevent oxidation of PCB assembly while the heating process.
In certain less crucial operations, the oxygen concentration in a nitrogen soldering reflow process may be more than 500ppm or as low as just 10ppm. SMT reflow ovens that can handle nitrogen frequently come with an oxygen monitor and an automated gas sampling device.
Working of a Modern Solder Reflow Oven
It is necessary to apply heat to the solder paste until it reaches a point of molten point which is 217°C for lead-free solder SAC305. To effectively solder surface-mounted electronic components to the PCB. The molten alloy will combine with the pads of copper on the PCB to form a eutectic mixture. Once it starts to cool to a melting point, a firm solder junction will develop.
In three different methods, heat can transfer from a source of heat to heated items.
· Conduction
When there is a temperature differential between adjacent locations, thermal conduction transfers across a substance without the material moving; when two items with very different surface temperatures come in touch with each other, it happens up until they reach the equalized temperature, heat moves from the hotter to the colder item.
· Radiation
Heat transmission by radiation takes to happen in electromagnetic waves form, mostly in the IR or infrared area. The mode of thermal transfer known as radiation doesn’t require any physical connection between the source of heat and the warmer object. Since black bodies absorb greater heat energy than white bodies, radiation has this constraint.
· Convection
Heat transfers from one location to another through a process called convection, which involves the flow of fluids like air or gas vapor. Moreover, it provides a contactless way of transferring heat.
The term “responsible” refers to a person who is responsible for the action. Ceramic heat elements emit heat by infrared radiation, but they do not immediately transport that heat to a Circuit. To ensure uniform heat production, the heat energy will first move to a heat adjuster. The heated air will force into an inner compartment by a convection blower or fan. Any location on the target Circuit board will experience consistent heat.
Working Principle Of the Solder Reflow Oven
By liquefying the solder that has already been spread on the PCBs, reflow soldering achieves the electrical and mechanical connections between the pins or ends of Surface-mounted electrical components and the PCB pads. There are four temperature levels overall in the reflow oven: preheating, heating, melting, soldering, and cooling. Let’s discuss the operation of all these four zones using the Lyra soldering reflow oven just as a reference.
1. Lyra SMT Reflow Oven
The purpose of preheating is really to ignite or activate the soldering paste and prevent the quick, high-temperature overheating that occurs when components are submerged in the tin. The Lyra Soldering Reflow Oven’s objective is to warm the Circuit board to room temperature as quickly as feasible. However, the heating level needs to be kept within a reasonable range. If it moves too quickly, heat shock will happen, potentially damaging the PCB and its components. The solvent won’t evaporate quickly enough if it moves too slowly. Impact the Lyra Soldering Reflow Oven’s soldering performance. The temperature differential in the reflow oven at the rear phase of the Lyra Soldering Reflow Oven heating zone is rather considered a result of the quicker heating rate.
2. The Lyra SMT Reflow Oven Insulation Zone
The main goal of the Lyra Soldering Reflow Oven thermal resistant phase is to minimize heating temperature differences and maintain the heating temperature of every component in the oven. Give sufficient time in the region to guarantee that the fluxes inside the Lyra Soldering Reflow Oven soldering paste are properly volatilized and that the heating temperature of a bigger component catches up to the heating temperature of a smaller component.
The oxides or residue on the circuits, component pin, and solder balls are clean with flux at the outcome of the heat-resistant stage. Also, the entire PCB temperature is now balanced. After this part, it must emphasize that the temperatures of all electronic components also on SMA ought to correspond.
Otherwise, because of the unequal temperature of every part, reaching the reflow phase will result in a variety of poor soldering occurrences.
3. Lyra SMT Reflow Oven Soldering Zone
The temperature increases quickly as the Board moves into the reflow phase, causing the soldering paste to melt. The temperature of the oven is set higher in this section, causing the component’s temperature to increase quickly to its maximum temperature. When the Lyra Soldering Reflow Oven’s peak temperature is too low, it is simple to create cold solder junctions and inadequate wetting. When it is too much high, the epoxy glue material and the polythene part are more likely to experience delamination and coking. While excessive eutectic alloy compounds form and lead to brittleness. The soldering site influences the soldering intensity.
Pay close attention to the time of reflow in the Lyra Soldering Reflow Oven area of soldering to make sure it doesn’t get too long. If it does, the heater in a Lyra Soldering Reflow Oven can damage, the components may well not work as well, the PCB may burn, and other negative things may happen.
4. Lyra SMT Reflow Oven Cooling Zone
To harden the solder junctions at this point, the Lyra Soldering Reflow Oven’s temperature lowers underneath the solid-state temperature. The cooling rate impacts the integrity of solder junctions. An excessive amount of eutectic alloy compounds may be formed if the rate of cooling is too sluggish. The soldering spot is susceptible to creating a big grain structure, which reduces the soldering point’s strength. It just has to cool down to 75°C because the cooling phase typically cools at a rate of 4°C/S.
The Role Of SMT Reflow Oven In The Soldering Process
The most important step in the entire reflow soldering procedure is the reflow oven. The reflow soldering process for Surface-Mounted components typically employs infrared or convection ovens. These ovens provide a variety of zones with adjustable temperatures. In a conveyor-like line, the zones permit different stages of cooling and heating.
The size of the oven must be appropriate for the load factor and production rate. They will decide both the oven’s minimum production line speed and the process’s repeatability. The oven’s size depends on whether the production processing speed limit is higher than the speed of the line. Often, a bigger soldering reflow furnace will be required for a greater-scale operation.
The Parts & Stages of SMT Reflow Oven
Along their manufacturing line, reflow soldering ovens solder employing a variety of steps and procedures. The PCB moves along the conveyor line or belts the entire time. One-sided woven conveyor straps or belts use in certain reflow ovens. A double-sided, edged conveyor line, however, guarantees greater precision and efficiency for bigger tasks. The oven can operate on both surfaces of a PCB thanks to a double-edged strap or belt.
1. Preheating Stage
The slow stepping up of a PCB to a certain temperature where the solder can reflow is a crucial component of soldering reflow.
Careful observation requires throughout the pre-heating. The PCB and electrical components may damage if the process of pre-heating carries out too quickly. The PCB is protected from harm by gradually boosting the temperature during the pre-heating step. Moreover, it guarantees that all components and parts are correctly and uniformly heated.
The temperature in IR ovens should rise by 2-3 degrees each second.
2. The Thermal Soak
During pre-heating, the PCB goes through a process of thermal soak. The Circuit board keeps at a certain temperature it attains, which was before throughout this stage. Before starting the reflow soldering process, a thermal soak raises the temperature of all elements to a comparable level.
Depending on the PCB and its components, the thermal soak takes a different amount of time. A soak period of an oven needs to complete in less time if it is more effective. Yet, it is important to watch out for an excessively high soaking temperature. Otherwise, flux exhaustion may occur.
3. The Reflow Stage
The procedure moves on to the reflow step after a process of thermal soak. The temperature of the oven has now risen over the melting level of a solder paste. The paste melts and turns into a liquid as a result of the temperature. The solder joints on the PCB will form from this liquid. The flux inside the solder is what drives the process. At the joints, it lowers surface tension and promotes metallurgical bonding.
The ideal temperature must maintain during the soldering reflow phase. This will result in soldering that is efficient and of good quality. Also, it is essential to confirm that the soldering reflow duration is accurate. Ineffective joints may result from insufficient heat. The PCB and its electronic components may become damaged as a result of excessive heat.
Typically, the reflow stage lasts between 30 and 60 seconds. Once more, it’s crucial to avoid having an excessively short or extended reflow time. If the length is too short, the solder cannot stay beyond its melting temperature long enough just to create strong connections. Too much time might cause the joints to deteriorate.
4. Cooling Stage
The PCB has to go through a cooling process after the soldering paste has cooled to produce the joints. This will give the molten solder time to solidify and secure the components. Similar to pre-heating, cooling must also be done gradually to protect the PCB from tension and damage. The PCB should typically cool at a melting temperature of 30 to 100 degrees, with a rate of cooling approx 3 degrees each second.
It is impossible to overstate the significance of progressive cooling. Proper execution of this technique will guarantee the production of connections that are safe and sound mechanically.
