PCBA Tech - Structural Features of PCBA Testing

PCBA board need to be tested beforehand before they are used. They can only be used if they pass the test. If they do not pass the test, they cannot be used. However, there are many problems to consider when testing PCBA boards. First of all, you should know the main content of PCBA Testing, then what are the basic contents of PCBA board when testing.

1. Aging test is mainly to keep PCBA board and electronic products powered on for a long time, keep them working and observe if any failure occurs. After aging test, electronic products can be sold in batch.

PCBA plates are often heated to produce a larger temperature difference than PCBA plates. Once the temperature difference exceeds the standard, it will cause poor welding, so we must control the temperature difference during operation. The thermal design of PCBA plates is constructed from many parts, each of which has different characteristics of action.

If the temperature difference is large, it will also cause poor welding, such as QFP pin opening, rope suction, pillar of chip element, displacement, shrink and fracture of BGA solder joint, we can solve some problems by changing the heat capacity.

(1) Thermal design of heat sink pads. In the welding of heat sink elements, there will be less tin in heat sink pads, which is a typical application that can be improved by heat sink design.

PCB circuit board can be designed by increasing the thermal capacity of the cooling holes. Connect the cooling holes to the inner grounding layer, if the grounding layer is less than 6 layers. Partial cooling layers can be isolated from the signal layer, and the aperture can be reduced to the minimum available aperture size.

(2) Thermal design of high-power grounding sockets. In some special product designs, sockets sometimes need to be connected with multiple ground/level layers. Because the contact time between pin and tin wave during peak welding is very short, it is usually 2~3s. If the thermal capacity of sockets is large, the temperature of lead may not meet the requirements of welding, forming cold solder joints.

To avoid this, a design called the Star Crescent is used, which separates the chip factory's weld hole from the electrical layer by passing a large current through the power hole.

(3) In the thermal design of BGA solder joints, there will be a special phenomenon of "shrinkage fracture" due to unidirectional solidification of the solder joints under the mixing process. The basic reason for this defect is the characteristics of the mixing process itself, but it can be improved by optimizing the BGA corner wiring to make it cool down slowly.

Based on the experience provided by the case, generally the welds with shrinkage fracture are located at the corners of BGA. By increasing the heat capacity of the BGA corner welds or decreasing the heat conduction speed, they can be synchronized with other welds or cooled afterwards to avoid the phenomenon that the welds are pulled off under BGA warping stress due to cooling first.

2. ICT test mainly includes circuit on-off, voltage and current values and fluctuation curves, amplitude, noise and so on.

3. FCT test requires IC program burning, simulates the function of the whole PCBA board, finds problems in hardware and software, and equips necessary production tools and test stand.

4. Fatigue test is mainly to sample PCBA board from PCBA factories and perform high-frequency and long-term operation of functions to observe whether failure occurs and to judge the probability of failure in the test so as to feedback the working performance of PCBA board in electronic products.

5. Testing under harsh environment mainly exposes PCBA board to extreme temperature, humidity, dropping, splashing and vibration to obtain the test results of random samples, so as to infer the reliability of the whole PCBA board batch products.