What is Tomstoning?

One end of the chip element is off the ground, as shown in below Figure .

Tomstoning pictures

How Tomstoning happen?

(1) The solder paste melting time at both ends of the component is not synchronous or the surface tension is different, such as poor printing of the solder paste (one end is defective), deviation, and different sizes of the component solder ends. Generally, the melted end of the solder paste is pulled up.

(2) Pad design - The pad extension length has an appropriate range (For exg.0201:0.1-0.2mm), and if it is too short or too long, it is easy to stand a monument, as shown in below Figure.

(4) Temperature curve setting - Tomstoning generally occurs at the time when the solder joint begins to melt, and the heating rate near the melting time is very important. The slower, the better to prevent Tomstoning.

(5) One welding end of the component is oxidized or contaminated and cannot be wetted. Special attention should be paid to components with single-layer silver solder ends.

(6) The pad is contaminated (screen, solder resist ink, foreign matter adhesion and oxidation).

How to prevent Tomstoning?

Design:

The pad shall be designed reasonably, that is, the extension size must be reasonable, and the wetting angle of the pad's outer edge (straight line) formed by the extension length shall be avoided as much as possible.

Production site:

(1) Wipe the screen frequently to ensure that the solder paste deposition pattern is complete.

(2) The placement of the patch is accurate.

(3) Use non eutectic solder paste and reduce the heating rate during reflow welding (controlled at 2.2 ℃/s).

(4) Reduce the thickness of solder paste.

Incoming materials:

The quality of incoming materials shall be strictly controlled to ensure that the effective area of two welding ends of the device used is the same (the basis for generating surface tension).