미국에서 유학을 하기 전에는 납땜이라는 단어를 들어보고 대충 무엇인지는 알고 있었지만, 자세히는 잘 몰랐다. 하지만, 박사과정 중 실험 물리를 선택하게 되므로써, 실험실에서 사용하는 Soldering(한국어론 인두 혹은 납땜)에 대해서 공부 및 정리를 해야할 필요가 생겼다. 아래는 대략적으로 필요한 납땜에 대해서 필요한 내용 혹은 기초적인 내용들을 정리한 것들이다.
1. What is soldering?
A process of making electrical bonds between two metals using the solder with a lower melting point than the base metals. Usually, for an electric contract between two different metals, a common soldering material is so-called solder, which is the alloy of lead. The key idea of soldering is mostly to get rid of oxidation layers on the surface of metals with a very light acid called flux, which prevent metal-metal bonding.
NOTE: Terminologies related to soldering
1) Base metal (or parent metal): The metals that we want to attach
2) Solder: The metal whose melting point is lower than that of the base metal.
- The solder is used as a bond to attach the base metals
NOTE: Difference between Soldering and Welding
1) Soldering: By melting the solder, two metals are bonded
2) Welding: By melting the base metal itself, it leads to that two separate metals are bonded
2. Types of solder
| types | Description |
| Lead soldering | - Ration: Sn:Pb = 60:40 - Melting point: 183~190 C - Low work difficulty and low prices - used for hobbies or educational purpose |
| Lead-free soldering | • Ration: Sn > 95% • Melting point: >200 C • Due to high melting point, soldering iron with high power is needed • Rather expensive than lead soldering • Replaced with lead soldering to satisfy ROHS • NOTE: The lead-free solder usually has flux in the solder, which helps to bond the solder to the base metal. However, because the flux contains harmful elements such as halogen, rosin, solvent, and etc, it is important not to inhale the vapor even during lead-free soldering |
3. The items for the soldering
| Item | Descriptions |
| The soldering iron | • Appropriate temperature of the tip for soldering: 350 Degree • If the temperature of the soldering iron tip is too hot, it causes the iron's lifespan to be shortened and the device to be damaged. |
| Soldering leads | • Lead soldering or lead-free soldering |
| Paste (solid) Flux (Liquid) |
a. The role of the soldering paste/flux • Cleaning the soldering iron • Playing a role in adhesion between the lead and the part • prevent the base metal from being oxidated during soldering • removal of the oxidation on the base metal • help the solder spread evenly on the base metal (e.g., helpful for wetting) • improve the electric conductivity b. Types of flux: Rosin flux, No-clean flux, and Aqueous flux • Rosin flux: made up from pine tree sap - The flux for general purposes such as electric devices. - Able to be removed from isopropyl alcohol. - slightly acidic, helping dissolve built-up gunk and oxidization - the activated rosin flux can leave behind chloride ions and other corrosive residues. • No clean flux - Essentially the same as rosin flux, but usually contains natural gum rosin with much lower concentration than rosin flux - designed to help circuit board manufacturers skip the time and expense of cleaning the board after soldering - leave much less residue behind than the typical Rosin flux • Water-soluble flux (or organic acid flux) - made from the organic materials such as citric, lactic, and stearic acid - more effective in removing metal oxides - should never left on a soldering surface, especially a circuit board - easy to clean it with water |
| Soldering stand | |
| Desoldering pump | a. How to use it? After melting the solder, suck it using the desoldering pump. |
| Soldering wick | |
| Soldering tip cleaner |
4. How to solder?
1) Using the soldering iron heated around 350 degrees, apply the heat on the PCB part or joints where the soldering will be applied.
2) Apply solders to the tip of the soldering iron and the PCB part
3) If the melted solder is spread well around where you want, then stop applying the solder and remove the soldering iron from the place.
Tip for soldering 1: After finishing soldering, thin the tip of the soldering tool to protect it from oxidation. In order to do that, put a small amount of solder on the tip and cover it on the surface of the tip with flux.
Tip for soldering 2: Do soldering as quickly as you can.
5. Possible problems during soldering
| Possible Problems | Description |
| Lack of an enough amount of solder |
|
| Short | |
| Applying too many solder | |
| cold-solder joint (냉납) | • Note that the lead should not be directly touched with the soldering iron. This leads to so-called cold-solder joint. It should be touched with the circuit or PCB part. |
| heating | • If the heated soldering iron is touching the device too much, it can cause the damage in the device. |
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