Soldering Techniques Explained in Electronics Fabrication
Soldering technology is a basic skill in electronic production. It is stipulated in the syllabus of labor skills in middle schools that students should: learn to use electric soldering irons, and master general welding methods. Welding technology mainly includes: scraping, enamelling, welding and other processes.
1. Preparation for welding
First of all, it is necessary to check whether the insulation performance of electrical equipment and electric soldering iron is good, so as to prevent problems before they happen; at the same time, emergency measures must be formulated, and students must be strictly required to observe discipline, because students' failure to obey discipline is the biggest hidden danger of accidents. Solder (generally use solder wire), soldering iron stand, solder box, flux (generally use rosin), wire strippers, peach pliers, tweezers, etc. The selection of electric chromium iron should be equipped with soldering irons of different powers depending on the size of the weldment. 20w internal heating electric soldering iron is usually used in electronic production.
2. Specific operation method
(1) There are usually two ways to hold the soldering iron: "pen holding style" and "knife holding style". Using an internal heat soldering iron usually uses the "hold the pencil" method (shown in Figure 1).
(2) When welding, the distance between the ferrochrome head and the tip of the operator's nose should be about 20cm.
3. Soldering steps
(1) tinning of electric soldering irons and weldments. General weldments include component leads, wires and printed circuits. The tinning process of wires and component leads can be decomposed into processes such as stripping, scraping, and enamelling. These processes can be demonstrated with the help of slides, pictures, and videos.
The enamel of the soldering iron tip. Both the new soldering iron tip and the oxidized soldering iron tip need to be tinned before using the soldering iron tip. Before tinning, first polish it with sandpaper or a fine file to expose the copper luster. The new soldering iron tip can be rubbed back and forth along the blade surface on fine sandpaper. In this operation, students should be reminded to use light force and not to smooth the blade surface. After grinding and cleaning, it can be turned on and heated for 2 to 3 minutes. The tip of the soldering iron will start to "eat" the tin, and then it will be repeatedly ground on the fine sandpaper with rosin particles until a thin layer of tin is hung on the blade surface. This operation is essential. Otherwise, during the heating process of the soldering iron, uneven tinning will occur due to rapid oxidation. For a soldering iron that has been used for a long time, if there are pits on the blade, you should use a file to smooth the pits before tinning.
2) tinning of wires and component leads. Wires generally have an insulating sheath, and stripping the insulation sheath of the wire end can be done with wire strippers, scissors and other tools, and the method of grilling with matches is not recommended. The peeling length of the end skin is generally about 1cm.
The wire ends and component leads must be "scraped" to remove the surface oxide layer before soldering, so that they can be soldered with tin. When cleaning, you can refer to Figure 2 and use the broken surface of the scrap steel saw blade or sandpaper to scrape the lead wire lightly to remove dirt and oxides. A short section of the root of the lead wire should be left unscratched to prevent the root of the lead wire from being scraped off and causing damage to the components. After scraping the multi-strand wires one by one, twist the multi-strand core wires into a rope as shown in Figure 3.
First learn to judge the proper working temperature of the electric soldering iron. When the soldering iron is energized for 2 to 3 minutes, touch the tip of the soldering iron to the rosin. If the rosin makes a sound and emits white smoke, it means that the temperature of the soldering iron is appropriate and can be used for soldering. Put the scraped wire or component lead on the rosin, press the lead lightly with the tip of the soldering iron, move along the lead while turning the lead, so that the lead is evenly coated with a layer of tin.
(2) welding
1) Welding essentials. Use scrap components and wires as weldments for practice. Lap the lead wire of the component with the solder joint, dip the soldering iron into an appropriate amount of solder, and keep the tip of the soldering iron close to the solder joint; when the solder at the solder joint is completely melted, gently turn the soldering iron tip to remove the excess solder, and then tilt it 45 degrees from above. Remove the solder joint quickly in the angular direction. Before the solder at the solder joint is completely solidified, the clamp or needle-nose pliers holding the lead wire should not shake at all, otherwise it is very easy to cause false soldering. This is the key to ensuring the quality of solder joints.
2) False welding. Welding is the formation of solder joints on the surface between components, printed boards, and solder joints, but the internal circuit of the solder joints is not connected, and the lead wires of the components are in poor contact with the solder joints, causing the circuit to be on and off at times. It is advisable to use visual teaching aids for virtual welding in teaching, so that students can deeply understand the harm of virtual welding to the normal operation of the whole machine circuit, and explain the main reasons for virtual welding.
There are many reasons for false welding. The tin quality of the lead wire and the printed board before welding is not high; during welding, the weldment is not clamped stably; the temperature of the soldering iron is too low or too high; the flux does not meet the requirements, etc.
3) Desoldering. When desoldering, the temperature of the soldering iron should not be too low; the tip of the soldering iron generally does not need sulfur tin. When the soldering iron touches the weldment for a moment, the component should be pulled out quickly. When pulling out the components, do not use too much force to avoid damaging the components. The desoldering part should be cleaned in time, and it is necessary to carefully check whether the adjacent circuit is short-circuited or opened due to desoldering.
