subject: E-Knowledge: SMT reflow soldering techniques and introduction-SMT soldering machine, reflow soldering machine - electronics industry [print this page] E-Knowledge: SMT reflow soldering techniques and introduction-SMT soldering machine, reflow soldering machine - electronics industry
Welding technology in the electronics assembly occupies an extremely important position. General Welding divided into two categories: one is mainly applied to through-hole electronic components and PCB welding? Wave, the so-called wave (wavesoldering) that is soft solder melting solder by electric pump or electromagnetic pump jet peak into the design requirements of the solder, so that pre-printed board with electronic components by solder wave crest to achieve components with the PCB solder pad or pin end of the mechanical and electrical connection between the soft soldering welding; the other is mainly applied to surface mount components and PCB welding? reflow (reflowsoldering), also known as re-flow soldering, reflow soldering is through the so-called re-melted pre-assigned to the PCB pad of soft solder solder paste, solder-side components for surface mount or pin and the PCB pad mechanical and electrical connections between the soldering, to achieve a certain reliability of the circuit functions. With surface mount components in electronic products widely used surface mount reflow soldering techniques and technology into a major technology. Its main technology features: The flux of metal to be welded surface cleaning (removal of oxide), to make good on the solder wetting; supply of molten solder to wet the metal surface; in the solder and welding metal intermetallic compounds formed between ; also enables micro-soldering.
Reflow soldering is in advance of PCB Welding parts (pad) cast proper and appropriate forms of solder paste release surface mount components, solder reflow using an external heat source to the welding required by the group or by point welding. Reflow and wave soldering in comparison with the following features:
1, do not like the wave soldering components as needed to direct immersion in molten solder, so parts are subject to the thermal impact;
2, reflow the site only need to solder on the cast, a significant reduction in the use of solder;
3, solder reflow can control who discharge to avoid defects such as bridging the generation;
4, when the components have a certain deviation from posted up here, because the role of molten solder surface tension, cast in the correct position as long as the solder, reflow soldering can automatically correct this minor error, so that components fixed in position on;
5, can use local heating source, which can be used in the same substrate for different reflow soldering process;
6, solders are generally not mixed with impurities, the use of solder paste for reflow solder can be formed to maintain the right.
Reflow soldering techniques are classified according to heating methods are: vapor phase reflow, infrared reflow, infrared hot air reflow, laser reflow, hot air reflow soldering, and tools such as heating.
Reflow temperature curve theory: From the temperature curve (see Figure 1) of reflow principle: When the PCB into the heating zone (dry zone), the solder paste in the solvent, the gas evaporate, while the flux solder paste wetting pad component terminal and pin, solder paste softening, collapse, covering the pad, the pad, component pins and oxygen separation; PCB into the heat zone, so that PCB and components are fully preheated suddenly into the welding zone against PCB excessive heat damage to PCB and components; when PCB into the welding zone, the temperature rose rapidly to reach molten solder paste, liquid solder pad on the PCB, components and pin ends wet , diffusion, overflow or return mixed to form the solder joint; PCB into the cooling zone, so that solder solidification, to complete the soldering.
Temperature curve is critical to ensure welding quality, the actual temperature curve and solder paste temperature profile of the temperature slope and the peak temperature should be consistent. 160 temperature rise before the speed control in 1 / s ~ 2 / s, if the temperature slope too fast, on the one hand and the PCB heating component fast, easy to damage the components, could easily lead to PCB deformation; the other hand, solder paste in the solvent evaporation rate is too fast, easily spilled metal components, resulting solder ball. Peak temperature is set higher than the melting temperature of solder paste 20 ~ 40 or so (for example, the melting point of solder paste Sn63/Pb37 183 , the peak temperature should be set at about 205 ~ 230 ), back (again) flow time for the 10s ~ 60s, the peak temperature is low or back (re) flow time is short, will not fully welded, solder paste does not cause serious melting; peak temperature is too high or back (re-) long stream, resulting in oxidation of metal powder, affect the welding quality, and even damage to components and PCB.
Reflow temperature profile, and back under the principles of the reflow soldering machines currently on the market are generally simple four-zone reflow machine, there are six large, eight-or 12-zone reflow soldering machine, which model QHL320A reflow soldering machine 20 programmable temperature control, the equivalent of 20-zone reflow machine, it will return the temperature curves, and thus more precise temperature control, more fitting ideal reflow profile to achieve optimal welding.
Where good welding quality protection? QHL320A reflow machine in addition to full compliance with reflow in the control of outside temperature curve, but also allows users to truly understand the principle of reflow soldering. QHL320A reflow machine with the functions of large transparent window, users can have transparent windows throughout the entire welding process control, solder paste can be observed simultaneously in the whole state of the welding process changes, easy to find the problems in the welding process, through the parameters adjustments to improve, to ensure good quality of welding. Meanwhile QHL320A reflow soldering machine for small desktop machine, all-static soldering, effectively prevent a large-scale multi-zone reflow machine crawler transfer resulting from small vibrations, the vibration may be in the flow of molten solder paste soldering area state of the small space between IC (Such as distance 0.5mm) and components (such as 0603,0402 and 0201, etc.) affect the welding, leading to the drift component, solder balling, solder bridges welding defects, and all welding is still completely avoid these potential defects.
Set back (again) reflow soldering temperature profile of the authority:
1, according to the temperature curve using the solder paste to set. Different metal content of the solder paste has a different temperature profile, solder paste manufacturers should be provided in accordance with the temperature curve of the specific product set back (again) reflow soldering temperature profile;
2, under the PCB material, thickness, whether the multilayer, size, etc.;
3, under the surface mount board carrying components of the density, size and availability of components of BGA, CSP and other special components set.
4, according to the specific equipment, such as: the length of heated area, plus
