Small Batch PCB Assembly Manufacturing

2022-11-29 15:30:43 Small Batch PCB Assembly 269 Viewed

SummaryTo understand where the cost of small batch PCB assembly is high, we need to decompose the entire link of contracting labor and materials. PCBA is a PCB assembly, including circuit board light board, component welding, SMT and DIP plug-in post-soldering. For the most part, the price of light b...

To understand where the cost of small batch PCB assembly is high, we need to decompose the entire link of contracting labor and materials. PCBA is a PCB assembly, including circuit board light board, component welding, SMT and DIP plug-in post-soldering. For the most part, the price of light boards on the market is more favorable for small batches, and the prices of components are basically open and transparent in major shopping malls, which can be compared for reference.

Small Batch PCB Assembly Cost

Since there is no possibility of price increase for the main PCB circuit boards and components, the cost of small batch PCB assembly is reflected in the assembly process. The main costs of small batch PCB assembly are as follows:

1. Prototype fee for smt chip processing

Small batch PCB assembly and SMT processing will vary in price depending on the number of points and packages. Large quantity and high price are the industry consensus. The larger the component package size, the easier it is to mount, and the corresponding poor quality will be reduced. Therefore, there is more room for communication in terms of price.

2. Welder hours after DIP plug-in

The plug-in material link involves special-shaped parts and material molding, and this link requires a lot of manual participation. Because there is no production capacity reference of machinery and equipment, this link is the most difficult link to control the cost of small batch PCB assembly. At the same time, the current labor cost remains high, and the cost of this process is generally high.

3. Small batch PCB assembly testing fee

The test fee for small batch PCB assembly includes test fixtures, test equipment, test man-hours, etc., and the test of communication equipment also needs the assistance of optical fiber, ICT and other test equipment, and the corresponding labor and equipment loss need to be taken into account, but will not very high, some low-volume PCB assembly companies even test for free.

4. Small batch PCB assembly auxiliary materials fee

Solder paste, solder bar, flux, UV glue, oven fixture, the quality of solder paste and solder bar are the most important auxiliary materials in the entire small batch PCB assembly and processing link. In the same soldering area, the price of imported solder paste will be much higher, but the difference in the quality of welding is very obvious.

Selection of Small Batch PCB Assembly Components

In small batch PCB assembly, on the premise of meeting the functional requirements of the circuit, components with high sensitive voltage threshold should be used as much as possible. Because the electrostatic and discharge sensitivity of a circuit board depends on the components with the lowest sensitive voltage threshold in the circuit board. Reasonable selection of components can effectively improve the success rate of small batch PCB assembly. The following points should be noted for the selection of small batch PCB assembly components:

1. Limit the output current, which can avoid the lock-in effect of CMOS circuit.

The lock-in effect means that there are parasitic PNP transistors and NPN transistors on the internal structure of the CMOS circuit during small batch PCB assembly, and a parasitic PNPN thyristor structure is formed between them. This interlocked positive feedback structure may be triggered by external factors (such as electrostatic discharge), and current will flow through the PNP tube (or NPN tube), and then pass through another parasitic NPN tube (or PNP tube) to make the current Amplified, and due to the positive feedback effect, the current is getting larger and larger and eventually burned. It can be seen that limiting the current so that it cannot reach the level of maintaining the locked state is one of the issues to be considered for CMOS devices when small batches of PCB are assembled.

A common solution is to use a resistor to isolate each output from its cable, and use two high-speed switching diodes to clamp to VDD (sink supply) and VSS (source supply) with cables.

2. Use a filter network

When assembling a small batch of PCB, a long input cable is sometimes required between the CMOS circuit system and the mechanical contact. At this time, the possibility of electromagnetic interference is increased, and the use of a filter network should be considered. At the same time, long input lines are bound to be accompanied by large distributed capacitance and distributed inductance, which is easy to form LC self-excited oscillation, resulting in the burning of diodes in the protection network. The solution is to connect a resistor in series at the input end, and its resistance value can be selected according to the formula R=VDD/1mA.

3. RC network

Where it is feasible, small batch PCB assembly can reduce the impact of electrostatic discharge by using an RC network composed of a resistor with a large resistance value and a capacitor of at least 100pF for the sensitive input of bipolar devices.

4. Avoid floating the input pins of CMOS devices

In small batch PCB assembly, it is necessary to prevent the input terminals of the CMOS devices that have been soldered to the circuit board from being suspended. At the same time, it should be noted that all unused redundant input leads on the CMOS device are not allowed to be suspended. This is because once the input terminal is suspended, the input potential will be in an unstable state, which will not only destroy the normal logic relationship of the circuit, but also easily cause electrostatic breakdown, external noise interference and other phenomena. The redundant input ends should be dealt with separately according to the function of the circuit.

Small Batch PCB Assembly Test Frame

PCBA test stand is widely used in the whole process of small batch PCB assembly and manufacturing. It is mainly used to test small batch PCB assembly boards after SMT patch and DIP plug-in. Among them, the ICT test is the main one, that is, through test points to test the electrical continuity of the circuit board to determine whether the entire PCB board is successfully welded. The PCBA test stand is the main tool used to assist in completing this test.

The quality of the PCBA test stand is related to the efficiency and pass-through rate of ICT testing. Due to its long-term frequent operation, there are high requirements for its production quality, which requires sufficient attention from small batch PCB assembly manufacturers.

Small Batch PCB Assembly Processing

1. In the process of small batch PCB assembly and processing, solder paste is required. For the newly purchased solder paste, if it is not used immediately, it must be stored in an environment of 5-10 degrees. In order not to affect the use of solder paste, it must not be placed in a sub-zero environment.

2. During the small batch PCB assembly process, the placement machine equipment must be checked frequently. If the device ages or some parts are damaged, the device must be repaired or replaced with a new one in order to ensure that the patch does not bend. Only in this way can the production cost be reduced and the production efficiency be improved.

3. During the small batch PCB assembly process, if you want to ensure the quality of PCB board welding, you must always pay attention to whether the setting of the reflow soldering process parameters is very reasonable. If there is a problem with the parameter setting, the quality of PCB board welding cannot be guaranteed. So usually, the furnace temperature must be tested twice a day, at least once. Only by continuously improving the temperature curve and setting the temperature curve of soldered products can the quality of small batch PCB assembly and processing products be guaranteed.

Environmental Requirements for Small Batch PCB Assembly

The processing technology of small batch PCB assembly has certain requirements on the workshop's power supply, ventilation capacity, temperature, humidity, air cleanliness, anti-static, and production personnel's wearing accessories. And the workshop environment tends to be more clean and tidy, with the purpose of reducing the health hazards to workers such as oil and dust. At the same time, environmental protection and greening are the pursuit and goal of modern development, because the environment of environmental protection and greening can reduce or control the generation of pollution sources. It can be seen that the material particles are relatively large, which mainly affects the visibility in the workshop, which affects the operation of workers in the workshop and the supervision of managers. At the same time, visible particles often greatly reduce the service life of air conditioning systems and equipment in the workshop.

1. Temperature and humidity requirements

For the normal operation of the equipment and the high standard requirements for the production process, it is best to control the ambient temperature of the small batch PCB assembly workshop at 23 ± 3 degrees Celsius, and the best relative humidity is 45%-70%R.

2. Ventilation capacity

Reflow soldering and wave soldering equipment have exhaust and fume emission requirements, and small batch PCB assembly manufacturers should configure exhaust fans according to equipment requirements. For all hot blast stoves, the minimum flow rate of the exhaust duct is generally required to be 14-15m/min.

3. Power requirements

The power supply voltage and power meet the requirements of small batch PCB assembly and processing equipment. Stable voltage generally requires single-phase AC220V (220±10%, 50/60Hz), three-phase AC380V (380±10%, 50/60Hz). If the requirements cannot be met, a regulated power supply is required, and the power of the power supply is greater than the power consumption of the device. The power supply of the placement machine requires independent grounding, and generally a three-phase five-wire wiring method should be used. Because of the high operating speed of the placement machine, it is easy to generate electromagnetic interference when connected with other equipment, which affects the normal operation and placement accuracy of the placement machine.

4. Static protection requirements

IC and other precision electronic components involved in small batch PCB assembly production are often easily damaged by static electricity, so electrostatic protection is also very important. Usually, personnel entering the workshop must wear anti-static work clothes, work caps, and shoes. gloves and wear anti-static wrist straps.

The workshop is the core of the small batch PCB assembly factory, and regular training on the environment and personnel requirements of the small batch PCB assembly workshop is an indispensable and important link.


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