Solder ball
In a solder ball ( English solder ball ), it may also comprises a small sphere from which soldering material , the reflow or vapor phase soldering of solder paste , in the tinning of printed circuit boards with HAL surface or in a wave soldering formed. Furthermore, it can be the test specimen when soldering paste is melted in the context of the solder ball test.
Solder ball test
In the solder ball test , a defined amount of solder paste is applied in a predefined geometric distribution to a substrate with good thermal conductivity and then melted. After melting, the merging of the molten solder to form a solder ball and the remaining amount of solder paste on the printing surface are observed and evaluated.
Solder balls for electrical connection in the ball grid array
Ball grid array components (BGA) are electrically connected to the circuit board by soldering. Here, spherical structures made of the solder material (= solder balls ) are formed between the contact point in the BGA and the copper surface of the assembly . These solder balls are somewhat flattened in the contact area of the BGA and the copper surface of the circuit board. Depending on the grid of the BGAs, the solder balls can have a diameter of 1.0 mm to 0.3 mm.
Solder balls as a component of solder pastes
For reflow soldering is solder paste needed. These pastes consist of solder balls of different sizes, depending on the type of paste. Depending on the manufacturing process, these spheres can sometimes have a teardrop-shaped appearance. Another main component of the solder paste is the flux. Flux and solder balls are mixed into a paste and can be applied to the printed circuit board to be assembled using a printing template and squeegee , for example .
Solder balls as a defect image
Reflow soldering
The solder balls adhere to the circuit board due to the flux contained in the solder paste . The solder balls usually have a very small diameter, typically smaller than 0.1 mm. The solder balls are always in non-wettable places on the circuit board (e.g. areas covered with solder mask ). In the case of wettable surfaces (copper surfaces without solder mask), the solder balls would immediately melt during the reflow soldering process and flow onto the copper surface.
The solder balls occur more frequently with solder pastes with very small paste components. The solder balls also occur more intensely if the circuit boards with the printed solder paste have been standing for a long time after the paste has been printed and liquid components have evaporated during this time.
Furthermore, the soldering profile used also has an influence on reflow soldering. A very fast soldering profile, in which the assembled assembly is heated up very quickly in the reflow oven, tends to lead to an increased number of solder balls.
Vapor phase soldering
With vapor phase soldering, the probability of the occurrence of solder balls is significantly lower than with the reflow soldering process.
Wave soldering
Solder balls can also be produced during wave soldering. This occurs more intensely when soldering in a protective gas atmosphere (e.g. nitrogen ) with a small amount of flux. When passing through the wave, small amounts of liquid solder splash away, which can stick to the circuit board as small solder balls.
Printed circuit boards with HAL surface
In the case of circuit boards with a HAL surface (HAL = hot air leveling ), liquid solder is applied to the copper tracks and metallized vias . To do this, the circuit board is immersed in liquid solder after the copper surfaces have been cleaned and treated with flux. The liquid solder is then blown off with hot air. This can also lead to the formation of small solder balls and the solder balls sticking to the circuit board.
Possible risks
If the adhering solder ball loosens during later operation of the assembly, it can possibly cause a conductive connection, for example a short circuit. In addition, there is the risk that the distance between two adjacent conductor tracks on the circuit board is reduced in an impermissible manner.
Rework of the assemblies
The solder balls usually only stick slightly to the circuit board. They can be removed by brushing the assemblies. The brush loosens the solder balls from the flux residue. The remaining flux residue itself usually only detaches from the circuit board after intensive brushing.
literature
- Reinard J. Klein Wassink: Soft soldering in electronics . 2nd Edition. Eugen G. Leuze, Saulgau 1991, ISBN 3-87480-066-0 .
- Wolfgang Scheel (Hrsg.): Assembly technology of electronics . Verlag Technik et al., Berlin et al. 1997, ISBN 3-341-01100-5 .
Individual evidence
- ↑ Reinard J. Klein Wassink: Soft soldering in electronics. 1991, p. 564 f
- ↑ Wolfgang Scheel: Module technology of electronics. 1997, p. 12 f
- ↑ a b c d e f g h Reinard J. Klein Wassink: Soft soldering in electronics. 1991, p. 618 f
- ↑ a b Reinard J. Klein Wassink: Soft soldering in electronics. 1991, p. 508 f