PCB microelectronics is increasingly in demand for highly advanced and sophisticated small form factor products like IoT devices, wearables, and similar portable devices. In this regard, PCB fabrication is also advancing — technology speaking — simply due to the fact microelectronics assembly demands precisely fabricated circuit boards.
Keep in mind that PCBs going through microelectronics assembly are considerably more special due to the intricacies involved. That includes utmost precision required for placing bare die on the circuit board and the critical cleanliness of the board before and after a bare die is attached.
In effect, fabrication is vital because it serves as the base on which the total and successful microelectronic assembly process depends on.
There are special aspects associated with PCB fabrication for microelectronics assembly. Read our recent column in SMT007 Magazine to get a good handle on this subject. Meanwhile, here are some tips and hints to bring you up to date.
• Fabrication shops working on PCBs for microelectronics assembly should have ISO9001 certification at the minimum, but even better, ISO13485 and AS9100 and other certifications.
• PCB fabrication for microelectronics assembly demands excellence in board and substrate co-planarity, process flow and control, and verification.
• Fab notes for specifying pad definitions the PCB layout engineer provides must include precise tolerances. Otherwise, pad inconsistencies result, as shown in Fig. 1. Pad #3 is only 0.060 millimeter (mm), while Pad #2 is 0.069 mm, a difference of over 12 percent in pad dimensions.
• Fiducial marks are important for microelectronics assembly. A bare die should have fiducial marks because they allow a programmer or process engineer to perform die attach programming.
• Precision in the pick and place operation is key to defining process control in microelectronics assembly.
• An EMS provider with a PCB microelectronics assembly line must have in place an incoming fabrication quality control check.
The verification process is the critical step to assure assembly was properly performed. Highly advanced and sophisticated tools, like a Keyence digital microscope, are ideal for their very precise measuring capabilities, inspection, and verification for die attach and wire bond applications. These verification features are necessary to detect virtually any defect in the whole manufacturing process that is not visible using regular inspection tools.