The packaging types that are prone to problems in SMT surface mount processing mainly include micro components such as QFN, BGA, 01005/0201, as well as pin QFP and LGA. These problems are mainly caused by small size, thermal stress sensitivity, or solder invisibility.

1. QFN package (pinless square flat package)
Common problems: Bridge connection, virtual welding, voids, warping.

Main reasons:
The solder pads are located at the bottom, making visual inspection difficult. During reflow soldering, uneven solder paste printing can easily lead to bridging or virtual soldering.
If the bottom heat dissipation pad is not designed properly, gas cannot be discharged during welding, forming voids that affect heat dissipation and reliability.
Uneven heating during the reflow process can lead to warping and cracking of solder joints.

2. BGA packaging (ball grid array packaging)
Common problems: solder joint voids, virtual soldering, stress fracture, bridging.

Main reasons:
The solder balls are hidden under the chip, and the soldering quality depends on the reflow curve and the amount of solder paste control. If the void rate exceeds the standard, it will reduce the thermal cycle life.
Large BGA is prone to stress fracture of solder joints during cooling due to mismatched CTE (coefficient of thermal expansion).
Small pitch BGA requires extremely high precision for steel mesh opening, and even slight deviations can cause bridging or insufficient welding.
3. 01005/0201 ultra small chip components

Common problems: misalignment during installation, standing monument, missing parts, poor welding.

Main reasons:
The size is extremely small (01005 is only 0.4mm × 0.2mm), and the precision requirements for the placement machine are strict (it needs to be ≤± 0.03mm). Ordinary equipment is prone to cause placement deviation.
Uneven heating of the two end pads or asymmetric amount of solder paste can easily cause tombstoning phenomenon.
The reflow soldering heats up too quickly, causing the component body to crack due to thermal shock, which is an implicit defect.
4. Close pin QFP/SOP (pin spacing ≤ 0.65mm)

Common problems: Pin bridging, virtual soldering, pin deformation.

Main reasons:
Pin density, slightly larger openings in the steel mesh, or offset solder paste printing can cause bridge short circuits.
Excessive surface mount pressure or inaccurate Z-axis control can cause pin collapse or deformation.
The Wicking effect during reflow soldering causes the solder to climb up the pins, resulting in insufficient wetting of the solder pads.
5. LGA packaging (pinless grid array)
Common problems: poor contact, voids, poor coplanarity.

Main reasons:
Relying on direct contact between solder pads and LGA pads, if the PCB has poor coplanarity or uneven distribution of solder paste, it is prone to local poor contact.
Uneven heating during the welding process can easily form micro voids at the connection interface, affecting signal integrity.
6. Fine pitch connectors and micro switches

Common problems: Bridge connection, open welding, internal resin ingress.

Main reasons:
Long connectors may crack solder joints due to PCB deformation and inconsistent layout direction during reflow.
The micro switch structure has capillary channels, which allow flux or rosin to penetrate into the interior during soldering, affecting electrical performance and lifespan.