Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON (small-outline no leads), is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes.
A QFP or Quad Flat Package is a surface-mounted integrated circuit package with “gull wing” leads extending from each of the four sides. Socketing such packages are rare and through-hole mounting is not possible. Versions ranging from 32 to 304 pins with a pitch ranging from 0.4 to 1.0 mm are common.
There are three main types of defects in QFP and QFN:
1. The pins or solder joints connected to the PCB are poorly soldered.
There are multiple pins on the right side of the QFP above.
Pin solder voids
2. Internal gold wires of QFP and QFN chips are disconnected.
The gold wire above is good.
This kind of problem is relatively rare because the chip will be inspected before leaving the factory, but the gold wire may still disconnect during transportation.
3. Poor soldering between chip body and PCB.
This problem is relatively common, but most manufacturers have no requirements for this defect, as long as the chip can be fixed on the PCB.
The X-ray image of the excellent soldering QFP chip is as follows. There are almost no voids in the pin, the gold wires inside the chip are not disconnected, and there are almost no voids in the chip body.