Reflow profiles or processes that are not well optimised can lead to poor or non-wetting, damaged components or cold soldering.Īfter soldering the boards are inspected in detail. The processed board is cooling down in the last zones of the reflow oven, the solder alloy solidifies and makes the solder joints. The component that has the lowest maximum temperature allowance will define the maximum temperature. This maximum temperature must remain under the maximum allowed temperature of the components. Furthermore, the evolution of the IMC layer and microstructure during thermal cycling was very similar for all four alloys 52Sn58Bi, 42Sn57Bi1Ag, LT 47 and LT 51 and all reflow profiles studied. In the third section the solder paste is melted and the process reaches its maximum temperature. Reflow profile did not have a dramatic impact on the IMC thickness or microstructure of the reflowed solder joint. The Temperature gradient is important because too quick changes of temperature can cause damage to components.ĭuring the thermal soak the flux is activated to reduce oxidation of pads and leads of components and improve wetting. The aim of the preheating stage is to accumulate heat smoothly in the board and the components. Reflow solder profiles usually have four stages, preheat, thermal soak, reflow and cooling. Sn/Pb and Pb-free Reflow Soldering Temperature Profiles COMMON INFORMATION TB493Rev.0.00 of 3 OctoTB493 Rev.0.00 OctoTABLE 1. The solder profile is influenced by the number of layers in the PCB, the copper distribution on the board, the number and size of components. Solder profiles need to be optimised for each individual assembly job. Standard Solder Paste Reflow Profile for Kester Paste Containing Alloys: Sn63Pb37 or Sn62Pb36Ag02 0 20 40 60 80 100 120 140 160 180 200 220 240 0 30 60 90 120 150 180 210 240 270 300 Time (sec.) Temperature (o C) Pre-heating Zone (2.0-4.0 min. Multiple segments help to get an optimised heat transfer and minimum temperature differences between different points on the PCBA. These are long convection ovens with many heating zones that together create a soldering cycle.Įach heating zone of the oven has a regulated temperature set to the solder profiles for the assembly process. The solder paste melts during this process and cools down again to create a good solder joint. Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is. Technol.During the Pick & Place operation, components are glued to the board by the solder paste.Ī reliable connection is made during the reflow soldering process. Example of reflow soldering thermal profile. Zhao, Methods for Phase Diagram Determination (Elsevier, Amsterdam, 2011) JinGang Gao, Wu YiPing, Han Ding, Solder. Morgan, Mechanics of Solder Alloy Interconnects (Springer, Berlin, 1994) When two joints are placed on the sample the temperature increase is close to 20 ☌. The maximum temperature increase of the joint is substantial: 25 mg of the solder paste increases the joint temperature by about 15 ☌. Analysis of the temperature profiles obtained during the reflow processes in a real furnace shows that latent heat influences the surrounding temperature not only during the phase transformation, but also during the whole following passage of the sample in the furnace. There are advantages and disadvantages to each. I have used both a 50 reflow oven AKA a toaster oven and more sophisticated and expensive reflow ovens. The released latent heat from one joint increased the temperature of the surroundings and delayed the solidification process of the second joint. Depending on your budget, you can buy a reflow oven for 50, 50,000 or anywhere in between. While one peak was present during melting in DSC, two peaks were present during solidification of two joints connected by a resistor. Melting and solidification processes of two solder joints were investigated by both methods to determine the influence of latent heat on the surrounding temperature. The reflow process of SAC305 solder paste was investigated by differential scanning calorimetry (DSC) and measurement of the temperature profiles in a real continual convection reflow furnace.
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