What is actually meant by through-hole reflow?

As the term suggests, wired components continue to be used. Through-hole reflow, is the new soldering process and the term describes the facts, i.e. reflow is soldering with a reflow action. The wired components are mounted to the printed circuit board like SMT components. THR components can be incorporated relatively easily into an existing reflow production line. How they are mounted on the circuit board is left to the station operator to decide. They can either be installed by suction or with grippers. In either case, however, they are supplied in a form of packaging suitable for automated production, preferably Tape on Reel. This method of installing components can save time and, in turn, costs, and contributes to safeguarding production in high costs countries. Needless to say, THR components can also be designed as wave-solder components. Thus, care must be taken to ensure that e.g. the plastic can withstand high soldering temperatures and that the flow of heat can reach the requisite soldering point unhindered. Just as THR components are subject to a special design, the printed circuit boards must also be specially configured for the purpose. Thus, only plated holes with soldering rings on both sides may be used for THR components. The diameter of the holes should be 0.10 to 0.25 mm greater than the pin diagonals or diameter. The diameter of the locking ring should be approximately 0.6 mm greater than the hole. The solder paste is applied by way of a template or dispenser, care being taken to ensure that the holes are sufficiently filled with paste. The last phase is the reflow soldering process. The circuit board is passed through the furnace and is thereby brought slowly to the desired soldering temperature which is normally between 240° and 290°C. It is then cooled again to room temperature. At this temperature, the soldering paste becomes fluid and fills the holes by capillary action, soldering the THR components to the circuit board. A clean, effective solder has taken place if a solder meniscus is present on both the soldered side and the component side.

RIA CONNECT prefers protruding pins, given that the inspection of solder meniscus is always feasible on the solder side, whereas the component side is difficult or even impossible to inspect, due to the density of the components.

Surface mount technology - what is it?

This is a process whereby the pins of the components are soldered to the surface of the circuit board, rather than through it. As a result, the design and requirements of components of this type differ from wired components and usually occupy more space on the circuit board than their wired counterparts. The circuit board itself is subject to the usual SMT design specifications. The respective pad geometry suggested by the manufacturer should be followed. Large copper areas should not be directly soldered. The reflow process is similar to that used for THR components. SMT/THR soldering methods differ primarily in the diminished mechanical load capacity following soldering. For this reason, SMT components should always feature mechanical anchorage points. SMT components actually require more space on the component side, but only enough for a minimum of two anchorage points on the solder side. RIA CONNECT is of the opinion that the THR- and SMT-compatible connecting components, which are available today, can be integrated into modern reflow processes without any great difficulty. Properly used, they can make an important contribution to optimising the manufacturing costs of electrical subassemblies.

Process comparison