Forming, installation, soldering and cleaning of DIP components.

In this article, I will explain the nuances of industrial soldering of DIP lead components—the ones with long pins - and how they are soldered in different industries. I will divide the article into several sections, and I will try to explain each of them as much as possible:
 1) Methods of preparation for installing DIP components.
 2) Methods of mounting DIP components to through-hole.
 3) Methods for soldering DIP components and materials for soldering electronics.
 4) Cleaning of printed circuit boards with DIP components.
 5) Drying printed circuit boards in a closet.
 6) Control of soldering and cleanliness of printed circuit boards.

 Let me clarify right away that the installation of output DIP components most often occurs after soldering SMD components—that is, after the surface mount line. This is the most common technical process. There are continuous soldering lines in PCB assembly services where DIP components are installed immediately after surface components, but in any case, the DIP soldering stage is always after SMD components.

Before installing DIP components with long pins to through-hole, they must be molded - the pins must be given the desired shape and length. This can be done by hand, but it is time-consuming, expensive, and ineffective. No assembly hands can save you when you need to mold several tens of thousands of components.
 You can purchase molding machines that will cut off the excess length and shape the terminals you need. There are quite a number of molding machines for different tasks. If you have a unique component shape, you can create the molding (equipment) yourself. Draw, order, and work.

Hand soldering comes first. It's nothing you can do. Most companies soldering PCBs with hand soldering stations and soldering flux. In fact, the reasons are typical: lack of desire to invest in production equipment, lack of desire to delve into new solutions and think, lack of faith in the future, expensive loans, low margins, and fear of worsening margins by purchasing new equipment.
 In the second place - wave soldering. Many techniques exist, from hand assemblying to full-fledged conveyor lines for wave soldering. The principle is simple - liquid flux is sprayed onto the printed surface from below. Next, the printed circuit board is heated according to the profile principle in a conveyor oven above the heating elements. So that all significant and heat-intensive components do not absorb all the heat during soldering and are easily soldered, they must be preheated. The next stage is immersion in molten solder.
 In third place is selective soldering or mini-wave. The selection principle is selective soldering. A mini-wave with the same molten solder approaches the component terminal from below and melts 1 terminal. This way, there is a significant saving in flux, but in terms of speed, it is not always a winning option. The nozzle with molten solder must be passed individually over all the pins in the holes on the printed circuit board to melt them. This is the principle of selectivity.
 The fourth method is a soldering robot. This solution is not suitable for everyone and not always, but it is quite a good solution for some jobs.
 It must be remembered that after the DIP component is soldered, there should be no open, untinned metal areas at the pin-cut site. This is because the exposed metal at the cut site quickly darkens and corrodes, especially after subsequent cleaning. The terminals of modern pin components are made of alloys that quickly oxidize and rust. Keep this in mind and remember to tin the fully trimmed lead. There is no need to deliberately tin the leads if the leads are cut before the soldering process by any method.
 The next problem that often occurs is leaking components, such as relay housings, transformers, and so on. Before shipping a PCB with leaking components, they must be sealed using tape or a spot mask. Of course, this is all manual labor, which greatly increases the cost of production and the product itself.

Many enterprises find this area rather problematic. Due to the difficulties in organizing and the cost of consumables, the cleaning area is one of their least favorite. To use it effectively, many parameters must be taken into account. Let's look at them.
 Is it possible not to clean printed circuit boards after soldering at all? Of course, it is possible, but appropriate materials are necessary for the product to remain presentable. To avoid cleaning after soldering, it is required to use ROL0 No Clean fluxes, solder paste, and soldering wires exclusively. Remember that many customers care about the printed circuit boards aesthetics, which must be agreed upon with the customer in advance.
 Manual cleaning of printed circuit boards. It makes sense to use manual cleaning in very visible places. In this case, the printed circuit board must be soldered like in point 1 - with no-clean fluxes for soldering electronics. If you use a Diamond Flux FN231 – No-Clean ROL0 Gel Flux for Electronics, cleaning may not be necessary.
 Cleaning printed circuit boards with water. Water cleaning is one of the cheapest, but its use is associated with the preliminary preparation of technical processes. An effective cleaning method can be distilled water with reagents. Ready-made cleaning solutions are often sold.
 The principles of cleaning can be different - manual, bubbling, jet clean, but not ultrasound. Ultrasonic cleaning is not suitable for electronics since many components can be damaged and become unusable, and there will be many defects. Ultrasonic cleaning is ideal for metals - for cleaning stencils after soldering printed circuit boards and tools, but not for printed circuit boards.

After cleaning, the printed circuit boards must be dried in an oven at about 70 degrees Celsius within 1 hour. Any remaining liquids must completely evaporate after cleaning them from the printed circuit board and under the components.

Because the DIP components are pretty large, the soldering joints are visible. You can check it with an optical inspection standart or with your eyes using Vision microscopes. All inspection need to use IPC-A-610 standart.
Monitoring the cleanliness of printed circuit boards visually or using periodic laboratory measurements after cleaning occurs.
With other cleaning methods, monitoring the cleanliness of the surface is a periodic procedure. There is no point in testing every printed circuit board in a batch if they are all assembled using the same technology.
Control is carried out using reagents. A special dark-colored reagent is applied to the soldering areas of the dry printed circuit board, which is kept on the printed circuit board for about a minute and then cleaned off with distilled water. After drying, those soldering areas where we applied the dark reagent are checked. If there are flux residues at the soldering points, they will be painted. This is especially important in cases where the printed circuit board is soldered with water-cleaning fluxes, wires and pastes. Residues may begin to rust, and if you doubt the correctness of the washing technology, it is better to check.

Thank you for reading!