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, transport, and subsequent storage due to the hygroscopic properties of the base material. This can lead to significant problems during further processing, especially during thermal processes, and in particular to delamination. Please note the applicable recommendation of the IPC according to IPC-1601 (latest version).
Storage conditions and storage periods
To prevent additional moisture absorption by the printed circuit boards during storage and to maintain optimum solderability, we recommend the following parameters for storing our printed circuit boards:
Notes:
- Printed circuit boards should remain in their closed transport packaging until assembly.
- The solder surfaces of the printed circuit boards should not be touched directly with your hands to avoid contamination from grease or similar substances
- Printed circuit boards from opened transport packaging should be processed within a maximum of one week
Recommended parameters for tempering
Our printed circuit boards are already dried during the manufacturing process, but after shipping, neither the transport conditions nor the storage conditions are always optimal. For further processing, we therefore recommend drying (tempering) the printed circuit boards beforehand, especially after prolonged storage. This measure significantly increases manufacturing reliability.
Depending on the type and surface of the printed circuit board -> see also Table 3-1 from IPC-1601
Detailed explanation of the topic of moisture
Printed circuit boards are made of a wide variety of materials and combine many different properties. Most printed circuit boards consist of several layers. These are: copper foil, prepregs, and the core. Prepreg and core consist of resin with glass fabric; the term FR4 or base material is often used. One of the properties of printed circuit boards is that they can absorb and store moisture from the environment because they are hygroscopic (attract water).
Our printed circuit boards are always dried during the manufacturing process and shipped in closed, protective transport packaging. We also recommend leaving the printed circuit boards in the closed transport packaging until they are processed.
However, it cannot be ruled out that moisture will be absorbed again during transport and subsequent storage. Neither the transport conditions (sea freight, summer, winter, rainy days) nor the storage conditions are always optimal. The storage period can also have a negative effect, especially in the case of larger prefabricated quantities that are stored for a long period of time before processing and unprocessed circuit boards remain in the opened packaging. During further processing in thermal processes such as soldering, this can lead to significant physical reactions and thus deviations in the soldering process. These then manifest themselves, for example, as delamination of the printed circuit board or through 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 manufacturing process, which must therefore precede the thermal processes of further processing. At this point, it must be emphasized that rigid-flex printed circuit boards and multilayers should always be dried. The PCB design, the structure of the PCB, and the base material used also have an influence. In the case of flex layers or large copper areas, drying takes longer due to the structure. For all types of PCBs, further processing should take place immediately after the drying process has been completed. This is to prevent moisture from being reabsorbed.
The recommendation of IPC-1601 in Table 3-1 distinguishes between the different final surfaces (HAL, chemical gold, etc.) and provides temperature and time recommendations for this preparatory process step of drying. As described above, compliance with the IPC-1601 regulations reduces the risk in production and thus significantly increases production reliability.