PCBA Tech - PCBA assembly for various tests

PCBA assembly for various tests
In assembly, the bare board is filled with electronic components to form a functional printed circuit assembly (PCA), sometimes called a "printed circuit board assembly" (PCBA). In the through-hole technology, the pin of the component is inserted into the hole surrounded by the pad, so that the component can be firmly fixed in one position. In SMT surface mount technology, the components are placed on the CBA to align the pins with the pads on the surface of the PCB; the solder paste applied to the pads in the previous process can keep the components in place; if the surface is Mounted components are mounted on both sides of the circuit board, and the bottom components need to be glued to the circuit board with red glue. In both through-hole and surface mounting, the components are soldered.

1. SMT surface mount technology

There are a variety of soldering techniques used to connect components to the PCB. Mass production usually uses "pick and place machine" or SMT placement machine and bulk wave soldering or reflow oven, but skilled technicians can solder very tiny parts (such as 0201 package, of which 0.02 inches * 0.01 inches)) under a manual microscope, Use tweezers and a small soldering iron for small volume prototypes. Some parts cannot be soldered by hand, such as BGA packages.

Second, the difference between SMT technology and through-hole technology

Generally, through-hole and surface-mount must be combined in a single component, because some required components can only be used for surface-mounting, and other components can only be used for through-hole packaging. Another reason for using these two methods is that through-hole mounting can provide the required strength for components that may be subjected to physical stress, while the same component using surface mount technology can take up less space.

Three, PCBA assembly test

After the PCB is assembled, it can be tested in a variety of ways:

When the power is turned off, visual inspection, automatic optical inspection. The JEDEC guidelines for PCB component placement, soldering and inspection are usually used to maintain quality control during the PCB manufacturing stage.

1. When the power is turned off, simulate characteristic analysis and power-off test.

2. When the power is turned on, the physical measurement (such as voltage) can be performed in the online test.

3. When the power is turned on, the function test is only to check whether the PCB conforms to the design parameters.

In order to facilitate the test, the PCB can be specially designed with some test points. Sometimes these test points must be isolated by resistance. Online testing can also perform boundary scan test functions for certain components. The online test system can also be used to program non-volatile memory components on the board.

In the boundary scan test, the test circuits integrated into the various ICs on the board form temporary connection points between the PCB traces to test the correct installation of the IC. Boundary scan testing requires that all ICs to be tested use standard test configuration procedures, the most common being the Joint Test Action Group (JTAG) standard. The JTAG test framework provides a way to test the interconnections between integrated circuits on the board without using physical test probes. JTAG tool vendors provide various types of stimuli and complex algorithms that can not only detect faulty networks, but also isolate faults to specific networks, devices, and pins.

When the test PCB fails, the technician disassembles the faulty component and replaces or repairs it, which is called rework.