PCB Technical - PCB and PCBA are different and COB vs PCB design

PCB (Printed Circuit Board) is a basic assembly used to support and connect electronic components,providing electrical connections and mechanical support. 

PCBA (Printed Circuit Board Assembly), on the other hand,is the process of assembling electronic components onto a PCB to form a complete electronic circuit or device.1. Components and 

Functions

The PCB itself is an empty board,consisting mainly of an insulating substrate and a conductive copper layer attached to it.It provides only electrical conduction and structural support functions and has no real electrical function.

In contrast, a PCBA is the final product that contains the PCB and all the electronic components mounted on it, such as resistors, capacitors,integrated circuits,and other assemblies.PCBAs have full electrical functionality and can perform specific electronic operations such as signal processing and power management.

2. Manufacturing Process

The manufacturing process of PCB mainly includes several technical steps such as designing, laminating, etching, drilling, plating and surface treatment in order to form a stable circuit pattern.

The manufacturing process of PCBA, on the other hand, is carried out after the PCB production is completed, and mainly includes steps such as component preparation, assembly (e.g., surface mount technology SMT and plug-in insertion DIP), soldering, inspection, and testing to ensure that all components can work properly.

3. Application areas

PCBs are widely used in the electronics industry in a variety of devices, including consumer electronics, industrial control and automotive electronics and other areas, as the infrastructure to connect different components.

PCBAs are often used in more complex devices such as cell phone motherboards, computers and industrial equipment. The functionality of these devices depends on the quality and reliability of PCBA.

4. Cost and Value

PCBs are relatively inexpensive to manufacture and are often an essential part of mass production. PCBA, on the other hand, is more expensive because it involves advanced assembly, testing and quality control of components, but it directly affects the functional value and market selling price of the final product.

COB requirements for PCB design

Since COB does not have a lead frame for IC packaging, it is replaced by PCB. Therefore, the design of the PCB pad is very important, and Finish can only use electroplated gold or ENIG, otherwise gold wire or aluminum wire, or even The latest copper wire will have the problem of not being able to reach it.

1.The surface treatment of the finished PCB board must be electroplated gold or ENIG, and it must be a little thicker than the general PCB gold plating layer to provide the energy required for Die Bonding to form a gold-aluminum or gold-gold co-gold.

2.In the wiring position of the solder pads outside the COB Die Pad, try to make sure that the length of each solder wire has a fixed length, which means that the distance between the solder joints from the wafer to the PCB solder pads should be as consistent as possible, so The position of each welding wire can be controlled, and the problem of short-circuiting of the welding wires can be reduced. Therefore, the diagonal pad design does not meet the requirements. It is suggested that the PCB pad spacing can be shortened to eliminate the appearance of diagonal pads. It is also possible to design elliptical pad positions to evenly disperse the relative positions between the welding wires.

3.It is recommended that a COB wafer should have at least two positioning points. It is best not to use traditional SMT circular positioning points for positioning points, but use cross-shaped positioning points, because the Wire Bonding machine is doing automatic Basically, the positioning will be done by grasping a straight line. I think this is because there is no circular positioning point on the traditional lead frame, but only a straight outer frame. Some Wire Bonding machines may be different. It is recommended to design with reference to the performance of the machine first

4.The Die Pad size of the PCB should be slightly larger than the actual wafer. One can limit the deviation when placing the wafer, and it can also prevent the wafer from rotating too severely in the die pad. It is recommended that the wafer pads on each side are 0.25~0.3mm larger than the actual wafer.

5.It is best not to have via holes in the area where COB needs to be filled with glue. If it cannot be avoided, then the PCB factory is required to completely plug these via holes 100%, in order to avoid the penetration of the via holes into the PCB during Epoxy dispensing. On the other side, causing unnecessary problems.