A surprising fact about Solder Paste is that many failures can occur before the solder paste jar is even opened. Many of the issues that arise during production are actually related to how the paste is transported, received, stored, and handled.
By monitoring and controlling the solder paste throughout transportation and storage at the facility, many production-related issues can be prevented. This is why proper control of the transportation, receiving, and storage processes is essential to maintaining solder paste quality.
Solder Paste consists of two materials with different densities: metal powder and flux. As a result, some solder pastes may experience flux separation, where the flux rises to the surface of the paste. Excessive heating further accelerates this phenomenon. It can also negatively affect the paste's properties, preventing it from flowing and spreading as intended. Therefore, every effort should be made to avoid exposing the paste to elevated temperatures.
Humidity –
Humidity is considered a contaminant that can negatively affect solder paste performance. All solder pastes tend to absorb moisture, making it important to prevent exposure to environments with high humidity levels.
Moisture can cause oxidation of the solder powder. As a result, the active chemicals in the paste will be consumed in removing oxidation from the solder particles rather than performing their intended function of cleaning components and PCBs. This can lead to poor wetting or even complete lack of wetting.
Humidity can also cause solder paste slumping after printing, which may result in shorts. In addition, moisture can lead to solder ball formation after reflow and significantly reduce the working life of the paste between printing and component placement. The ideal printing environment for solder paste is 40%-50% relative humidity and a controlled temperature of approximately 22-26°C.
Airflow directly over the stencil area should be avoided, as it can dry the paste too quickly.
Preparing Solder Paste for Use – Proper preparation is essential to ensure optimal performance. Never use solder paste while it is still cold. Opening the container before the paste reaches room temperature can cause moisture condensation on the surface of the paste, leading to issues such as slumping, solder balls, flux spattering, and wetting problems.
The paste must reach room temperature before opening and use. Typically, it requires approximately six hours after removal from refrigeration to reach room temperature.
The container and its inner seal must not be opened until the solder paste has fully reached room temperature.
Under no circumstances should the paste be heated artificially, such as on a hot plate or near any heat source. Once the paste has reached room temperature, open the container and gently stir it in a single direction for one to three minutes using a dedicated solder paste spatula. This ensures homogeneity and uniform distribution of all materials within the paste.
Overmixing may make the paste too soft, potentially resulting in slumping and short circuits.
Used Solder Paste – Solder paste that has already been used and removed from the stencil should be placed in a separate container and never returned to a container holding unused fresh paste.
When collecting paste from the stencil, care should be taken not to collect dried paste into the separate container. The collected paste can later be reused by mixing approximately 50% fresh paste with 50% previously used paste until the used paste has been fully consumed.
Storing used and fresh solder paste together in the same container may introduce moisture and other contaminants into the fresh paste.
For consultation and orders, please contact us or leave your details using the contact form, and our team will get back to you.