SMT patch processing tin beads cause
The tin bead phenomenon during SMT processing is one of the main defects in production. Because it has many reasons and is difficult to control, it often plagues SMT patches and engineering technicians.
First, tin beads are mainly concentrated on one side of the chip-shaped RC components, and sometimes appear near the chip IC pins. Tin beads not only affect the appearance of board-level products, but more importantly, due to the dense components on the printed board, there is a danger of short-circuiting the line during use, which affects the quality of electronic products. There are many reasons for the generation of tin beads, often caused by one or more factors, so it is necessary to prevent and improve them one by one in order to better control them.
Patch tin beads
2. Tin bead refers to some large solder balls. Before the solder paste is soldered, the solder paste may exceed the printed pad due to various reasons such as collapse and being squeezed. When soldering, these are beyond the pad. The solder paste is not melted together with the solder paste on the pad during the soldering process, and is formed near the device body or the pad.
3. However, most of the tin beads occur on the chip components on both sides of the chip component. For example, after the solder paste is printed, if the solder paste is exceeded, the solder balls are likely to be generated. The solder paste is melted together with the pad portion to form no solder balls.
However, when the amount of solder is large, the component placement pressure will squeeze the solder paste under the component body (insulator), and it will be melted during reflow soldering. Due to the surface energy, the molten solder pastes into a sphere, which has a tendency to raise the component. However, this force is extremely small, and the component is gravity-squeezed toward both sides of the element, separated from the pad, and forms a tin bead upon cooling. If the component has a large gravity and is squeezed out of the solder paste, a plurality of solder balls may be formed.
According to the formation of tin beads, the main factors affecting the production of tin beads in the SMT patch production process are:
(1) Stencil opening and land pattern design.
(2) Steel mesh cleaning.
(3) Repeatability of SMT placement machine.
(4) Reflow oven temperature curve.
(5) Patch pressure.
(6) The amount of solder paste outside the pad.
The above is the industry consultation provided by smt patch processing factory Shenzhen Pengzexiang Technology Co., Ltd., I hope to help you! Please contact us if necessary: http://www.oem-pcb.com email@example.com