General PCBA finished products process: warehouse → production line → production line upgrade software → assembly into a complete machine → QC test → write IMEI number → QA full inspection → restore factory settings → storage

Due to the shape of the IC, the line width is getting thinner and thinner, which makes the IC vulnerable to damage by EOS and ESD, causing permanent failure. Through analysis, it is found that the failure caused by EOS and ESD accounts for the top three. Although necessary measures are taken in the design to ensure the reliability of the IC, the damage to the IC by EOS and ESD cannot be effectively eliminated, and the devastating damage to the IC by EOS and ESD needs to be avoided through the control of the production process. At the same time, because the storage and use of ICs do not meet the requirements, it often results in "POP CORN" and "delamination" phenomena during SMT processing, which is also an important reason for IC damage. Here we explore how to avoid damage to the IC during the PCBA manufacturing process and promote the improvement of production quality.

1. IC packaging and storage

The surface of the plastic large-scale integrated circuit is hygroscopic. If the IC is exposed to the air for a long time, it will cause the so-called "POP CORN" phenomenon in the SMT process due to its absorption of moisture in the air. Bake before packaging or before use. The IC is baked for 7 hours at 125 degrees Celsius before it leaves the factory, and then vacuum-packed to ensure that it can be stored for 12 months at 40 degrees Celsius and a relative humidity of 90% or less. Within 72 hours (environmental requirement: 30 degrees Celsius relative humidity below 60%), the SMT soldering process is performed, otherwise the IC must be baked again. If the IC is not used within 72 hours, it must be baked to remove the IC moisture absorption problem. Baking conditions: Bake at 125 ± 5 degrees Celsius for at least 12 hours. After baking, an appropriate amount of desiccant should be added for vacuum packaging within 4 hours or SMT welding production should be arranged in time.

Inventory control principle: FIFO. The label on the vacuum bag describes the moisture sensitive device.

2. POP CORN phenomenon

When the molded package or the IC is exposed to a hot and humid environment, when the wafer and the resin, the wiring and the resin contain moisture, or the resin contains hydroxyl groups, it is hygroscopic and the water absorption rate increases. When soldering, the water vaporizes immediately. Expansion, as the resin also expands, causing the IC body to crack or break the wiring inside the IC. Therefore, pay attention to environmental requirements when packaging and storing the IC to avoid damage to the IC due to environmental factors.

2.1. EOS protection measures
Types of IC failure due to EOS (Electrical over stress): STP, LIGHTNING, ESD, EMP. These may cause metal compounds or bonding wires to melt and cause IC failure. EOS prevention:
1. Establish appropriate operating procedures
2. Ensure proper testing of the IC
3. Use a good power supply
4. Maintain a strict maintenance system for equipment / fixtures / transfer cards

2.2. ESD protection measures
Prevention of ESD (Electro-static discharge):
1. Reduce the source of electrostatic voltage
2. Staff wear anti-static wrist straps, conductive clothes and shoes
3. Wide use of antistatic or conductive direct or indirect materials
4. Establish a safe static work station, area
5. Make sure that the equipment does not generate static electricity above 200V
6. The factory environment maintains relative humidity at 40-60%
7. Use air dissipator to reduce the static voltage below 35V

3. Precautions for SMT assembly process

1.The pin size and tolerance setting of each IC component are input correctly.
2.Inspection and management of solder paste characteristics
3.SOLDER ALLOY CHART
4.PCB Management
5.REFLOW over-welding temperature control: Preheat and Soak, COOLING
6.REFLOW temperature curve and control
7.Stencil requirements and controls
Requirements: Generally, the opening of the IC stencil is 10 micrometers smaller than the IC PAD, which can prevent the solder paste from deviating from the PAD by 0.2 mm to form a solder ball. Without Undercut, it will prevent the solder paste from advancing during printing; the hole wall is smooth, and the front, middle and rear dimensions are the same.

4. PCB Inspection and Test

1.Use AOI: Automated Optical Inspection
2.AOI applied to SMT inspection
Missing parts: not affected by the style of the substrate
Offset: not affected by substrate pattern
Polarity Reverse: Components with polarity symbols
Tombstone effect, wrong parts, less tin, tin bridge, empty soldering, too much soldering

3.PCBA test uses ICT (IN CIRCUIT TEST) equipment. In the ICT test, pay attention to the FLUX residue caused by the test failure.