THT - Insertion THT - Insertion 04/02/2020
The technology of through holes
The technology of through holes , better known by the acronym THT of the English Through-Hole Technology is a technology that uses the holes practiced in the plates of printed circuit boards for mounting various electronic elements to create, electric bridges between one of the faces of the mounting plate to the other, by means of a conductive tube, which is usually an alloy of zinc, copper and silver, to prevent oxidation and allow welding. In these holes ( holes) components can be welded although the operation is not advised, because these THTs are usually inserted by a machine automatically, and their appearance once placed is similar to that of a tiny rivet. THTs are usually quite delicate and sensitive to heat. And if they get too hot, the contact between the tracks of one of the faces of the circuit and the other can be compromised, resulting in inoperative and rendering the plate useless.
THT circuit design process
- First, the circuit that has to work was designed. The components are calculated and data are collected on what these will be in shape, size, number and measure, energy and radio emission and consumption.
- After designing the circuit and after electrically designed. Knowing how the components are going to be connected, and their consumption, if the circuit is going to be very complex and you will need a large number of tracks, you may need a two-sided board.
- If a two-sided plate with many tracks is needed, to avoid the accumulation of many bridges, the use of THT technology is advised.
- Once this is decided, the circuit is designed and the plates begin to be created, which can be created in copper based on bakelite or fiberglass .
- The plates are a base plate with one or two sheets of conductive material on one or both sides. When its design is done, the unwanted driver areas are corroded, leaving the base free, creating electric paths or tracks that interconnect the different components with each other. Once the plate is created (this is what it is usually called), we proceed to give it a layer of varnish so that the tracks are not oxidized. Leaving the terminals free. The terminals are the points where the different components will be welded, and if varnished, the welding material would not grip.
- Once this is done, these terminals will be scheduled to allow the subsequent implementation of the components. The machinery that pierces the plates is usually robotic. And it is a machine with multiple bits that drills the plates, making several holes at the same time. The plates must be fixed and in the proper position so that the machine does not miss the hole.
- THT also receive a hole at this point, which is also generally between 1.7 and 3 mm, a thickness similar to the pinout of a high-power rectifier diode. In these holes the conductive tube that will join both sides of the circuit will be implanted.
- The next step logically is the implantation of the THT packages. The implantation is totally robotic, since the conductive rivet that joins the faces must be placed very carefully, because an excess of force can break the printed circuit. And a lack of it in the application of the rivet would mean a connection failure. The machine that places the through tubers works with three-dimensional numerical control technology, auto-CAD and has laser sensors to locate the position of the plate, which rotates depending on the position appropriate to the rivet you want to place. This is one of the questions why the use of this technology is so expensive.
- Once the tests are done and in the production phase the plates pass a quality control phase that measures their conductivity. That is, all of its tracks are continuous and there are no connection failures for when the components are soldered.
- In some cases, the conductive terminals of the plates are pre-tinned by passing them over a hot tin source whose temperature is so high that the tin vapor ends up adhering to the copper of the terminals.
- If the circuit is not viable it is discarded, if it has a slight fault it can be recycled.
- Once the insertion is complete, the plate passes slightly over a tin pool with a mixture of anticorrosive (resin) and silver (to prevent corrosion and weld shine) at the appropriate temperature and it adheres to the areas exposed to Welding at the ideal temperature, avoiding overheating. In the pool the tin waves, logically the components are only placed on one side, the upper one.
- Finally the plate is ready to be tested, if it does not pass the quality control, it goes to welding reviews or it is disregarded