Sunday, October 1, 2023

SMT soldering method and SMT Process

What is SMT process & SMT manufacturing?

SMT stand for Surface Mount Technology. SMT is replacement of “Through Hole Technology-THT”. 

Through hole technology is mounting scheme used for electronic components that involves the use of leads on the component that are inserted into holes drilled in PCB, solder to other side manually.

Through Hole technology is reserve for heavy & sulkier components. While SMT is advance,  increases manufacturing automation. SMT components have no leads. Actually there is no need of components leads to pass through the hole. It is adequate for components to be soldered directly to the
board. For this SMT was born.

SMT and Through Hole technology Difference

Before going further in details of PCB we have to understand some “Basic of Electronics here.

Electronics= study of the behavior of an electron under different conditions of externally applied fields. 

Electronic Components:-

There are 5 components- 3 Passive & 2 active

  • Active– Diode, Transistors & ICs
  • Passive– Resistor, Capacitor & Inductor

Active component:- Active components are those that deliver or produce energy or power in the form of a voltage or current.

Passive component:- Passive components are those that utilize or store energy in the form of voltage or current.

 In Simple PCB we found components like- Resistor, Capacitor, diode, LED, etc.

What resistor does in PCB?

Resistors receive a voltage and restrict the amount of current that flows through it. 

What Diode does in PCB?

Diode is an electronic component, which allows the flow of current in one direction. Diode serves as a gate keeper, allow current to flow at a certain minimum or break-over voltage, in one direction.  Most common type of diode is p-n junction diode.

What Capacitor does in PCB?

Capacitor is an electronic device that stores electric energy. The function of capacitors is to temporarily hold electric charge, and release it whenever more power is needed elsewhere in the circuit.

PCB Components details

What are leads in PCB?

Lead in electronic is an electrical connection from electric pole of an electronic part/Electronic components.

Through Hole technology is reserved for heavier & bulkier components (Electrolytic capacitor / semiconductor). SMT is advance technology, increase manufacturing automation. In SMT components have no leads, there is actually no need for component lead to pass through the board. It is
easy or adequate for component to be soldered directly though the board. For this SMT was born.

Leads in PCB board

What are Vias in any PCB?

It is an electrical connection between copper layers in PCB. The holes are plated hole (Gold plating). Copper layer are conductive rest material is non conductive.

What are vias in PCB

What are SMT components?

SMT components are design to set down on board. All SMT components are called SMC (Surface Mount comp). SMC are classified in Passive
SMD (Here resistor & Capacitor), Transistor Diode and Integrated circuit.  In PCB assembly process most of the components on board are placed automatically. SMC are smaller in size.

SMT components

What is SMT soldering?

SMT soldering is stand for surface mount soldering, and it is process of connecting SMD components which are mounted directly on to the
surface of PCB. The SMD connection by SMT is done using  solder paste.

The soldering processes required for SMDs during the PCB assembly needs to ensure the components are held in place during the soldering, the components are not damaged, and the final soldered quality is exceedingly high.

There are two main methods for SMT soldering:-

  1. Wave Soldering
  2. Reflow Soldering

What is solder paste?

Solder paste is a mixture of minute solder spheres and specialized form of solder flux. And solder flux is nothing but chemical substance used to clean the surface of PCB board. Since mixture of these two make paste like texture, so we call solder paste.

Solder flux is cleaning agent that helps in removing oxides and impurities from the surfaces. It helps in effectively soldering the joints by cleaning the surface.

Solder Grade:- Grade of solder depend upon size of solder ball. There are around 8 grade. Type1 to type 8- As the size reduce grade size increases.  Example- Type 8 solder paste grade- Solder ball size is 2~8 mm.

What is solder flux

What is Solder Flux?

It is chemical substance used in PCB assembly. It is cleaning agent that helps in removing oxides and impurities from the surfaces. It helps in effectively soldering the joints by cleaning the surface. 

Type of Solder Flux:-

  1. Rosin Based solder paste
  2. Water soluble flux paste
  3. No clean solder paste

Article on SMT process and PCB manufacturing is covered in next article. Visit for related article.

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