General information on the storage and processing of printed circuit boards
All PCB circuit boards with FR4 base materials or similar materials can absorb moisture during production, transportation and subsequent storage due to the hygroscopic properties of the base material. This can lead to considerable problems during further processing, especially in thermal processes, and in particular to delamination. Please observe the applicable IPC recommendation according to IPC-1601 (latest version).
Notes:
- Printed circuit boards should remain in the closed transport packaging until they are assembled
- The soldering surfaces of the PCBs should not be touched directly with the hands in order to avoid contamination by grease or the like
- PCBs from opened transport packaging should be processed after a maximum of one week
Recommended parameters for tempering
Our PCBs are already dried during the production process, but neither the transport conditions nor the storage conditions are always optimal after shipping. For further processing, we therefore recommend drying (tempering) the PCBs beforehand, especially after long periods of storage. This measure significantly increases production reliability.
Depending on the type and surface of the PCB -> see also Table 3-1 from IPC-1601
Detailed explanation on the subject of moisture
Printed circuit boards are made from a wide variety of materials and combine a corresponding number of properties. In most cases, printed circuit boards consist of several layers. These are Copper foils, prepregs and the core. Prepreg and core consist of resin with glass fabric, often referred to as FR4 or base material. One of the properties of printed circuit boards is that they can absorb and store moisture from the environment, as they are water-absorbent (hygroscopic).
Our PCBs are always dried during the production process and shipped in closed, protective transport packaging. We also recommend leaving the PCBs in the closed transport packaging until they are processed.
However, it cannot be ruled out that moisture will be reabsorbed during transportation and subsequent storage. Neither the transport conditions (sea freight, summer, winter, rainy day) nor the storage conditions are always ideal. The duration of storage can also have a negative impact here, especially in the case of larger prefabricated quantities that are stored for a long period of time until processing and unprocessed PCBs remain in the opened packaging. During further processing in thermal processes such as soldering, considerable physical reactions and thus deviations in the soldering process can occur. These then manifest themselves, for example, as delamination of the PCB or outgassing.
For the reasons mentioned above and based on industry-wide experience, the IPC-1601 regulations list drying as a necessary preparatory step for the assembly production process, which must therefore be carried out before the thermal processes for further processing. At this point, it must be emphasized that rigid-flex PCBs and multilayers should always be dried. The PCB design, the structure of the PCB and the base material used also have an influence. For flex layers or large copper surfaces, drying takes longer due to the structure. For all PCB types, further processing should take place immediately after the drying process has been completed. This is to prevent moisture from being trapped again.
The IPC-1601 recommendation in Table 3-1 differentiates here between the various end surfaces (HAL, electroless gold, etc.) and provides temperature and time recommendations for this preparatory drying process step. As described above, compliance with the IPC-1601 regulations reduces the risk in production and thus significantly increases production reliability.