What is Solder Paste? - National Products
CONTENTS
1. What is solder paste?
2. How many types of solder paste are there?
>Based on the particle size as per IPCJ – STD 005 Standard
>Based on flux type
>Based on material
3. Solder paste application key considerations
>Stencil thickness
>Aperture design
What is solder paste?
Solder paste is a material used in the electronics manufacturing process to create electrical connections between electronic components and printed circuit boards (PCBs). It consists of finely powdered solder alloy suspended in a flux medium.
Solder paste is applied to a stencil using a process called “solder paste printing.” This process is a critical step in surface-mount technology (SMT) assembly and ensures accurate deposition of solder paste onto the printed circuit board (PCB) before components are placed.
Paste applied in stencil in a solder paste printing machine
Solder paste applied on a PCB surface
How many types of solder paste are there?
They are classified into three main types as given below:
Based on Particle Size as per IPC standard J-STD-005
Based on flux type
Solder paste can be classified into three categories on the basis of flux type.
1. Halide Free (0% Halide) – ROLO
2. Low Halide (0.03% Halide) – ROL1
3. Halide Type (0.2%) – ROM1
Though it is commonly known that halide containing solder paste can effectively improve wetting, but due to some concern (or tradition) for electrical and chemical reliability, halide free productsare widely used.
Based on flux type
Leaded Solder Paste: Leaded solder paste refers to solder paste that contains lead as one of its primary alloying elements.
Lead Free Solder Paste: Lead-free solder paste is a type of solder paste formulated without lead as one of its primary alloying elements.
Solder paste application key considerations
Stencil Thickness
Stencil thickness ensures that the correct volume of solder paste is properly released from the apertures to achieve the required solder joint.
If the stencil is too thick, the paste may be held to the inner walls of the aperture by surface tension.
The following formula can be used to select the proper stencil thickness:
Stencil thickness
Aspect Ratio = Aperture width/stencil thickness
Area Ratio = Area of the pad (L*W)/ Area of aperture walls (2* (L+W) * T)
Aperture Design
Aperture design is to important to prevent the formation of solder defects. Mostly, apertures are designed to be a bit smaller then the pads to provide a good gasket seal between the stencil and the circuit board.
Aperture design