The Carbon Resistance PCBA/PCB
With the development of PCBA/PCB and component assembly towards short, light and thin, more and more manufacturers are participating in the development wave of integrated production of components(PCBA)and PCB.The production and application of conductive carbon oil plate are very extensive under the condition of PCB working environment and low requirement of resistance precision.JY Electronics — a rigorous and responsible manufacturer of PCBA.
This PCBA is made for one of our American clients. We had produced many PCBAs for this client. Those boards are used in flexible Rope CT, split-core transformers, toroidal current sensors and precision potential transformers.
This PCBA is the control board that we recently produced for them.
The single PCBA/PCB size
The single PCB size is 1.4 x 0.9 inches. Fabricate PCB in accordance with IPC-6012, Class 2; per IPC-6011. Material is FR-4 Tg140, the finished board thickness is 1.6mm ±10%. It has 2 copper layers, the finished copper thickness is 1 OZ of each layer. All holes are be located within 0.008” (0.2mm) diameter of true position.
Layer to layer registration be within 0.005” (0.125mm). All holes sizes are finished sizes using ±0.003” tolerance. Green color Solder mask on both sides. The surface finished technology is Lead-Free HASL RoHS compliant. Silkscreen is white, permanent, organic, non-conductive ink.
We designed as 3*4=12 single PCBs in one panel. All panels be stamp holes with 7mm edges on each long side of the panel Dimensions and tolerances are per ASME Y14.5-2009.
We have produced similar boards for this PCB in the same series of this customer.
In previous production, we found that the design of some 0402 capacitor and resistor PCB pads was not very reasonable.
It is found that poor welding is common in several parts after reflow soldering. After inspection and analysis, our engineer doubled that the reason is that the distance between the pads is too large,
so the contact range between the pins and the pads is very small; and the area of the pads is too large, so the tin cannot be well solder to the pins. Last time, we manual added tin to repair those poor soldering.
When the customer sent us the design this time, we focused on checking the capacitor and resistance pads of the 0402 packaged. After our checking, we found the same problem as last time.
In order to ensure the production speed and product quality, we represented our idea to the customer. After the customer modified the size and distance of the pads, he sent us the design of version 2.
In this version, the pads were so close together that engineers were worried about a short circuit.
After we told the customer the suggestion, the customer also understood and hoped that we could help adjust it. After our engineer made the adjustment
The customer checked and thought it was reasonable, so the final GERBER began production.
PCBA/PCB carbon oil resistive area
This PCB contains a carbon oil resistive area. Resistive values across this area must be held between 200 and 450Ω.
Among them, synthetic resin is equivalent to a carrier, play a bonding role; the hardener acts as a curing agent; the toner acts as a conductor of electricity.
How to control the resistance of carbon oil?
The resistance of carbon oil is related to the composition and thickness of carbon oil. Therefore, in order to achieve satisfactory resistance control, the following three requirements must be met:
- Reasonable in line with the process of square resistance value of carbon oil.
- Printing should reach a reasonable thickness.
- Torrefied thoroughly——temperature and duration must reach (oven: 150℃-170℃, 30-60 minutes; infrared furnace: 150℃, 15 minutes).
We tested the quality of the carbon oil.
Meet the following standards:
- Hardness: not less than 3H.
- Adhesion: Apply 3M tape to the same position for 3 times, and the carbon oil will not fall off.
- Heat resistance: 260±5℃for 5 seconds, carbon oil and PCB are not separated.
Before assembly, we also 100% inspected the resistance value of those PCB.
Firstly, we put the probes of the multimeter to the 2 solder pads of the carbon oil area. 95% of our PCB were meet the requirement of 200~450Ω. We gave the results to the customer, then the engineer asked to measure between these two points.
Our technician had measured all PCB with multimeter again according to customer’s requirement.
All components of this project will be purchased by our company. All components’ P/N and manufactures are as same as the customer’s original BOM. We purchased them from the China agent of manufactures and authorized suppliers.
The thickness of stencil is 0.12mm. All of the holes of the ≥0603 packaged are made solder bead protected.
This board is single-side SMD process. The carbon oil side do not need to assemble components. Before assembly, our IQC department checked all the components with PCB’s pads.
After the adjustment by the customer and our engineer, 0402’s solder pads match the components well.
After completing SMT, our QA inspector also inspected all the PCBA, especially the capacitor and resistor of these 0402 packages, and there was no poor soldering this time.
The customer is very grateful for our improvement for this project, which not only guarantees the delivery speed, but also guarantees the product quality.
After production of each project, we will record the problems and analysis our suggestions for improvement to the customer. JY Electronics — a rigorous and responsible manufacturer of PCBA.
We always insist that, as the core part of electronic products, good PCBA is produced, not repaired.
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