Tips to avoid PCB blistering
There are many factors involved in PCB delamination and blistering. Please refer to my last post. Cesgate gives some simple suggestions based on our own experience to help reduce PCB blistering.
1) Whether the stacking design and pattern distribution of the PCB are reasonable. It is necessary to consider the uniformity of heat distribution under thermal stress to avoid local overheating and expansion stress that exceeds the bonding force.
2) Board selection. Under lead-free, it is necessary to select boards that can meet the lead-free process, and pay special attention to the following thermal properties of the material, such as Tg (glass transition temperature), Td (thermal decomposition temperature), Z-CTE (thermal expansion coefficient), TMA T260\288\300 delamination resistance time, and water absorption of the board. For specific technical indicators, please refer to IPC-4101 (Specification for base materials for rigid and multilayer printed boards) standard.
2. PCB process
There are many aspects that need to be controlled in PCB processing, but Cesgate believes that the following points need special attention.
1) PP and core board storage. Moisture-proof measures should be taken, and temperature and humidity should be strictly controlled to ensure that the control conditions meet the datasheet requirements of the material supplier. At the same time, the board must be used within the validity period and cannot be used after the expiration date.
2) Browning process control. For the control of organic metal deposition, select high-quality browning solution and strictly monitor the contamination of the browning layer.
3) Lamination process control. Strictly follow the lamination curve provided by the board supplier to ensure that the material is fully cured, and regularly perform Tg and △Tg tests on the laminated boards.
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3. Inspection of incoming board materials
The typical process evaluation method for PCB is thermal stress + slicing method, which is the simplest and most practical method in PCB evaluation and the most economical method to detect abnormal incoming materials in advance.
4. Storage and use of boards
1) Storage conditions. Use vacuum packaging and the air permeability of the packaging material meets the requirements of EIA 583 (standard for packaging materials for moisture-sensitive items). The air permeability of the material is less than 0.02g/100in2/24hrs, and it has electrostatic protection and mechanical strength. In addition, the warehouse and production environment meet the temperature <=30℃ and relative humidity <=75%.
2) Unpacking and use of boards. In an environment with controlled temperature and humidity (temperature <=30℃, relative humidity <=75%) and no acid or sulfur, the unpacked PCB needs to complete the SMT process within 24hrs, and the Dip process within 48hrs after the SMT process is completed.
5. Assembly process
1) Reflow curve. It is recommended to set the temperature curve to meet the specifications and the solder joint quality to meet the quality standards in the early stage, and try to shorten the welding time and temperature to reduce the heating of the board.
2) Component maintenance. It is recommended to use automatic equipment to replace the components that need to be repaired, so that the heat input of the components and boards can be controlled and the consistency is better, which can avoid the phenomenon of local overheating causing PCB delamination and blistering.
Finally, it is particularly emphasized that unless it is certain that the PCB is damp, it is not recommended to perform unnecessary baking on the PCB. Baking itself is a "double-edged sword". On the one hand, it can indeed dehumidify, but it also has many negative effects. If the baking temperature and time are not set properly, the risk of stratification and blistering will be accelerated. At the same time, the PCB coating is also a test, which will accelerate the oxidation of the coating and affect its weldability. In particular, OSP surface treatment needs to be handled with caution.