PCB Assembly Introduction

There are two process for manufacturer to do PCB assembly.
Below picture show controle base plate(PCBA) exist everywhere in our house appliances.
Process of PCB assembly fabrication
(1) . Traditional DIP process
(2) . SMT process

Here first is the introduction of the process of DIP today.
1 . Traditional DIP process to PCB assembly means inserting the parts which with leg into the PTH hole of PCB.
2 . And then pass the PCB through tin soldering machine, to reach the purpose of soldering tin.                              

The structure of tin soldering machine

The structure of flux tank


The function of foamed pipe in flux tank
1. To air through the tiny holes on the foam tube body, causing numerous of air bubbles, with the number of air bubbles to cleave with flux, by metal accumulation, contact from the bottom of the base board and achieve the function of the flux coating, and then extra flux be strike off by air knife, and make flux distributed uniformly at the bottom of the base plate.

Method of flux coating
1. Bubble type flux coating
2. Wave type flux coating
3. Spray type flux coating

Hello I also would like to make simple introduction on flux which is used for assembly

A. The function of Flux
1. Remove the oxide on the surface of part and substrate
2.Reduce the surface tension of the solder and promote the flow of the solder
3.To protect the surface of the metal, avoid it to be oxidized under the environment of high temperature.

B. The main ingredients of flux
1.Rosin: it is refined from the grease of pine tree.
2.surfactant : Because of the gentle characteristics of rosin, it is not easy to remove the oxide, thus must add surfactant in order to enhance its effect.
3. Solvent: Dissolve and blend solid state material like rosin and surfactant, general multi-purpose isopropyl alcohol or ethylene glycol.
4. In addition, there are interface active agent, foaming agent and other ingredients

C. Variety of flux.
(1) Rosin flux :
1. R grade : Inactive rosin flux
2 . RMA : Weak activity rosin flux
3 . RA : Strong activity of rosin flux
4 . RSA : Super Strong activity of rosin flux

(2) Synthesis of active flux : This kind of flux is developed by DUPONT company, it’s advantage is can make the residue which caused after soldering can become liquid state, easily for cleaning.
Based on activity, it can be divided into:
SR–No active synthetic flux
SMAR – Weak active synthetic flux
SSAR – Strong active synthetic flux
SAR – Super strong active synthetic flux

(3). Water-soluble flux: The flux of organic acids, performs best help on welding, but must pay attention to the cleaning situation of the base board of welding after washing. If there’s residues, it will cause corrosion of substrate material, military and aerospace industry are banning the use of water-soluble flux process of substrate

(4). Disposable flux
Rosin kind improved flux: solid content 5-20%, residues will not cause corrosion to the base plate.