Wetting and solderability testing
The wettability and solderability of PCB and component metallization can be tested using standard tests (e.g. IPC-J-STD 002, IEC 68-2-20, IEC 68-2-54, IEC 68-2-58).
The following tests for evaluating the wettability and solderability of substrate metallizations and component connections can be performed at Fraunhofer ISIT:
- Wetting force measurement with the wetting balance test with video observation and documentation.
- In situ observation of the melting behavior
- Melting of solder pastes and preforms on a wettable substrate using a solder crucible (e.g. at temperatures of 235°C/245°C) - Wetting efficiency test
- Measurement of solder spreading behavior (spreading)
- Edge angle measurement in cross-section or by means of laser scanning microscope
- Solder balling test on a non-wettable substrate
Wetting force measurement with the so-called wetting balance (Fig. 1) is the preferred method for evaluating the solderability of components and printed circuit boards.
In wetting testing, the test specimen is immersed in a solder deposit (solder bath or solder ball) (Fig. 2).
The sensor in the wetting scale is a load cell that measures the forces during the immersion process on the test specimen. The surface tension and buoyancy of the solder deposit initially pushes the specimen upward, and as soon as the specimen wets, a force is generated that pulls the sample being measured into the solder.
This produces a force-time signal called the wetting force curve. Figure 3 shows the wetting force curves of various solder alloys.
Due to the different melting points of the solder alloys, the wetting results for the individual solder materials turn out very differently. Criteria for evaluating the wetting ability in the measurement curves are the wetting force, the delay time and the dynamics (gradient) of the wetting. These criteria are reflected both in the wetting force curves and in the wetting progress display in a video recorded in parallel.
A good wetting ability of surfaces is also expressed by a sharp contact angle (Fig. 4).
The wetting and solderability tests often become necessary when abnormalities occur in the soldering process and the desired joint quality is not achieved. The service offering for wettability evaluation addresses both component manufacturers to evaluate their products and assembly manufacturers to support the right product and material selection and application. ISIT offers technology consulting and support for process evaluation and optimization. We will be happy to answer your individual questions.