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The Air Quality Sensor Board

This PCBA was made for one of our American customers. This customer is in the smart home industry. The products produced by our company include circuit boards in modern household appliances such as bathroom heating, coffee machines, and air purifiers. This board is an intelligent monitoring board for this year's new generation of air purifiers. The customer first placed a sample order to us.

Air purifiers, also known as "air cleaners", refer to the ability to absorb, decompose or transform various air pollutants, generally including decoration pollution such as PM2.5, dust, pollen, peculiar smell, and formaldehyde , Bacteria, allergens, etc., products that effectively improve air cleanliness are mainly divided into household, commercial, and industrial. We produce household purifiers. This circuit board is a supervisor of air quality. Through the sensor, the air quality can be judged as good or bad in real time, and then the indicator light of the corresponding color will be lit, and instructions will be sent to another control board to control the on, pause and intensity of the purification function. And the supporting control board is also provided by our company.

This PCB is meet requirements and acceptance criteria per the latest revision of IPC-A-600 CLASS 2, IPC-6012, IPC-6011 CLASS 2. The material is FR-4, board thickness is 1.6 mm. The copper clad both sides. All copper thickness for the layers is 2.0 ounce (finished copper thickness). The surface finished technology is immersion gold 3U’’. The solder mask color is green, and silkscreen is white.

This PCB has the golden finger design. Before PCB production, our engineer asked the customer if the bevel should be made to facilitate the insertion and extraction of the golden finger. The customer replied that we did not need the miter cutting, so we produced according to Gerber design.

In order to facilitate SMT and improve production efficiency, we made 2 PCB in one panel. Due to the golden fingers, we have left some space between the two boards. The two long sides are each added with a width of 7MM to maintain stability. There are 4 positioning holes and asymmetric mark recognition points on the edge of the board. The mark’s center is 3.5mm away from the edge of the board, which is our company’s regular requirement. All the PCB are 100% electrically tested.

All components of this project will be purchased by our company. All components’ P/N and manufactures must be as same as the customer's original BOM. These components are well-known component brands. For example, the resistors are mostly Panasonic. The chips include Texas, Murata etc. The switch USES e-switch.

The senor is use for the air reaction, on this account, these sensors are very sensitive to what's in the air. Improper storage can affect its performance, and some chemical fumes can cause irreversible damage. These sensors must be stored in a controlled environment.  Humidity levels must be below 65%.  Exposure to chemicals vapors must be avoided at all costs. This includes conformal coating processes, silicone adhesives, silicone rubber, etc.  

When the purchase of these sensors arrives at our company, our warehouse technician firstly checked the quantity, and then give it to the IQC department to check the quality and compare with the soldering pads. We then put them in a special storage cabinet with the right temperature and humidity to avoid affecting the quality of the sensor.

This PCBA is one-sided SMD and DIP board. Before assembly, our IQC department checked all the components with PCB’s pads and DIP holes. After confirming that each component matches the PCB’s solder pads and holes exactly and passes the quality standard, they can be passed to the next progress--SMT. The package of the resistors and capacitors of this board are 0805. We made tin proof bead treatment on the stencil, so that the amount of solder paste can be well controlled and the soldering defects caused by too much solder paste can be avoided. We mount the resistors, capacitors, chips and other components of the SMT with high-speed automatic mounting machine, and then carry out reflow welding, The first panel must be checked to confirm that the SMT assembly has the correct parts at the required locations as defined in the assembly drawing. The positioning and alignment of the components will also be verified before the remaining panels are assembled. After SMT was completed, our DIP department manually welded the switches, connectors, but not assembled sensors at this period.

After this step, our QA department conducts full inspection on all PCBAs. Inspection of solder joints, solder shorts, proper solder wetting to components’ pins, proper solder fill of all vias and through hole pads. These PCBAs are in good welding condition and do not need to be repaired.

Next, we arrange to clean the surface of the board. We use dust-free cloth, brush and special cleaning agent to clean the circuit board surface of impurities, flux, etc. Generally speaking, it is necessary to assemble all the components before cleaning the board. But as mentioned above, the sensor hasn't been welded yet. Why? The acids and outgassing from soldering and cleaning could result in sensor contamination.  It is to use rosin flux with minimal chlorine content.  In mass production, wave soldering of the sensors is not availiable as the flux vapors may affect the sensors. So we will still manual solder the sensors after cleaning.

The previous generation of air sensor boards required to be programmed and tested before they left our factory. The installer is provided by the customer. According to the customer's instructions, we placed the four PCBAs in turn in the slot of the programmer, and then ran the programming software to install them. This time is the sample order of the new generation of products. We first updated the program for the programmer, and then operated the same steps to install the PROGRAM for PCBAs. When the green indicator light on the programmer stops blinking and keep light-on, it means the program is installed successfully.

The customer wanted to test the sample board by themselves, so after the program was installed successfully, we wrapped the circuit board with anti-static bubble film and carton, and deliver to the customer.

The customer tested it soon after they received it. All the sample boards we produced passed the test, and the customer was very satisfied. After a week later, the customer placed an order for thousands units of this sensor board to us.

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