Conformal coating also seen as PCB coating is a PCB assembly process which aims to protect the final PCBA products from nature damage and become more durable. Typically , the conformal coating material is thin polymeric film. The PCB assembly products which are processed by conformal coating can resistant some environmental factors, such as moisture, dust, salt, chemicals, temperature changes, etc.
- Requirements for conformal coating:
- A) Conformal coating thickness: coating film thickness control in 0.05mm-0.15mm.Dry film thickness 25um-40um
B)Secondary coating: In order to ensure the thickness of products with high protection requirements, secondary coating can be carried out after the film is fixed (whether to carry out secondary coating according to the demand shall be determined)
C)Check and repair: visually check whether the coated circuit board meets the quality requirements, and repair the problems. For example: DIP parts needle and other protection area touch coating, usable forceps clip depilate cotton ball or clean cotton ball dips in to wash board water to scrub its clean, pay attention to cannot wash off normal coating when swabbing.
- D) Replacement of components: After the curing of the coating, if you want to replace components, you can follow the following operation
a, Directly solder the components with ferrochrome.
b, Soldering alternative components
c, Use a brush dipped in conformal coating and brush coating on alternative components, and make the coating film side dry curing
- Operation requirements:
- A) Conformal coating workplace requirements clean, no dust flying, must have good ventilation measures, and prohibit the entry of irrelevant personnel
- B) Wear a mask or gas mask, rubber gloves, chemical protective glasses and other protective equipment during operation to avoid injury to the body
- C) After the completion of the work, the used tools should be cleaned in a timely, and the container with conformal coating should be closed and sealed tightly
- D) The circuit board should be done anti-static measures, not the circuit board overlap placed, coated process, the circuit board should be placed horizontally
- Quality Requirements:
- A) The surface of the circuit board cannot be flow coating, drip leakage phenomenon, brush coating pay attention to not drip to the local isolation part
B)The conformal coating side shall be flat, bright, thin and uniform, Need the solder pads, SMT component or conductor shall be well protected
C) The surface and components of the coating can not have bubbles, pinholes, ripples, shrinkage, dust and other defects and foreign substances, no powder, no peeling phenomenon, Note: the coating film have not dry before do not touch the coating film
D) local isolation of the components or areas can not be coated with conformal coating
E) Areas and components that cannot be coated with conformal coating:
a, routine not coated components: High-power radiator, heat sink, power resistors, high power diode, cement resistors, dialing switch, potentiometer (adjustable resistor), buzzer, battery holder, fuse holder, IC socket, light touch switch, relay, such as the type of socket, pin header, terminals and the DB9, DIP or SMD type light emitting diode (Non-indicating effect), digital tube, grounding screw holes
b, Areas and components that are not allowed to use the coating as specified in the drawing
c, According to the provisions in the details of “Non-coating components( Areas) catalog”, the components with conformal coating cannot be used
- F) If the conventional non-coated components need to be coated, the R&D department may specify requirements or the drawings may be marked for anti-coating to be coated.