Flex pcb welding

Flexible circuit board welding operation steps

Before soldering, apply flux on the pad and treat it with a soldering iron to avoid poor tinning or oxidation of the pad, resulting in poor soldering, and chips generally do not need to be processed.

Carefully place the PQFP chip on the PCB with tweezers, taking care not to damage the pins. Align it with the pad, and make sure the chip is placed in the correct orientation. Adjust the temperature of the soldering iron to more than 300 degrees Celsius, dip the tip of the soldering iron with a small amount of solder, press down on the aligned chip with a tool, add a small amount of solder to the pins at the two diagonal positions, and still Hold down the chip and solder the pins on the two diagonal positions so that the chip is fixed and cannot be moved. After soldering the opposite corners, re-check whether the position of the chip is aligned. If necessary, it can be adjusted or removed and re-aligned on the PCB.
When you start soldering all the pins, you should put solder on the tip of your soldering iron and coat all the pins with flux to keep the pins wet. Touch the tip of the soldering iron to the end of each pin on the chip until you see solder flow into the pin. When soldering, keep the tip of the soldering iron parallel to the pin to be soldered to prevent lapping due to excessive solder.
After all the pins are soldered, wet all the pins with flux to clean the solder. Blot off excess solder where needed to eliminate any shorts and laps. Finally, use tweezers to check whether there is any false soldering. After the inspection is completed, remove the flux from the circuit board, dip a hard-bristled brush in alcohol and wipe carefully along the direction of the pins until the flux disappears.
SMD resistance-capacitance components are relatively easy to solder. You can first put tin on a solder point, then put one end of the component, and use tweezers to clamp the component. After soldering one end, check whether it is placed correctly; Put it right, and then solder the other end.

Precautions for soldering flexible circuit boards

In terms of layout, when the size of the circuit board is too large, although the welding is easier to control, the printed lines are long, the impedance increases, the anti-noise ability decreases, and the cost increases; if it is too small, the heat dissipation decreases, the welding is not easy to control, and adjacent lines are prone to appear Mutual interference, such as electromagnetic interference of circuit boards, etc. Therefore, the PCB board design must be optimized:
Shorten the connection between high-frequency components and reduce EMI interference.

Components with heavy weight (such as more than 20g) should be fixed with brackets and then welded.

Heat dissipation issues should be considered for heating elements to prevent defects and rework due to large ΔT on the surface of elements, and heat sensitive elements should be kept away from heat sources.

The arrangement of components is as parallel as possible, which is not only beautiful but also easy to weld, and is suitable for mass production. The circuit board is designed as a 4:3 rectangle (good). Do not change the width of the wire to avoid discontinuity in the wiring. When the circuit board is heated for a long time, the copper foil is prone to expand and fall off. Therefore, the use of large-area copper foil should be avoided.

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