Whether the QFN package chip is well welded can be determined by the following ways:
Appearance inspection: Observe the welding area to ensure that the solder joint is uniform and smooth, and there are no obvious welding defects such as cracks, bubbles, or uneven solder distribution.
Use a magnifying glass: Use a magnifying glass or microscope to examine solder joint details, paying special attention to whether the solder is tightly attached to the pad.
Connectivity test: Use a multipurpose tester or multimeter to check whether there is electrical connectivity between solder joints to ensure that there is no short circuit.
Temperature test: Test the chip within the normal operating temperature range to see if there is an abnormal temperature increase, which may be a sign of welding problems.
Functional testing: Run the device or system to check that the chip is working properly and ensure that welding does not affect performance.
X-ray inspection: Sometimes it is necessary to use X-ray inspection to look at the internal structure of the solder joint to ensure that there are no hidden problems.
In short, the quality inspection of the welded QFN package chip needs to consider the appearance, electrical connectivity, functional performance and other aspects. If you are unsure or doubt the quality of the welding, it is best to ask a professional technician or equipment manufacturer to check and test.