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China Pcb Assembly Service Provider-Topscom
Jul 05, 2016

Pcb assembly service that are provided by companies In assembly the bare board is populated with electronic components to form a functionalprinted circuit assembly(PCA), sometimes called a "printed circuit board assembly" (PCBA).

Inthrough-hole technologycomponent leads are inserted in holes.Insurface-mount technology(SMT) the 

components are glued onpadsorlandson the surfaces of the PCB. 

In both component leads are then mechanically fixed and electrically connected to the board bysoldering.

suggest china supplier: China Topscom

There are a variety ofsolderingtechniques used to attach components to a PCB.High volume production 

is usually done withSMT placement machineand bulk wave soldering orreflow ovens, but skilled 

technicians are able to solder very tiny parts (for instance 0201 packages which are 0.02 in.by0.01in.)

by hand under amicroscope, using tweezers and a fine tipsoldering ironfor small volume prototypes. 

Some parts cannot be soldered by hand, such asBGApackages.

Often,through-hole and surface-mount construction must be combined in a single assembly because some 

required components are available only in surface-mount packages, while others are available only in 

through-hole packages. Another reason to use both methods is that through-hole mounting can provide 

needed strength for components likely to endure physical stress, while components that are expected 

to go untouched will take up less space using surface-mount techniques.For further comparison, 

see theSMT page.

After the board has been populated it may be tested in a variety of ways:

While the power is off,visual inspection,automated optical inspection.JEDECguidelines for 

PCB component placement,soldering,and inspection are commonly used to maintainquality control

in this stage of PCB manufacturing.

While the power is off,analog signature analysis,power-off testing.

While the power is on,in-circuit test, where physical measurements (for example, voltage) can 

be done.

While the power is on,functional test, just checking if the PCB does what it had been designed 

to do.

To facilitate these tests,PCBs may be designed with extra pads to make temporary connections.Sometimes 

these pads must be isolated with resistors. The in-circuit test may also exerciseboundary scantest 

features of some components. In-circuit test systems may also be used to program nonvolatile memory 

components on the board.

In boundary scan testing, test circuits integrated into various ICs on the board form temporary 

connections between the PCB traces to test that the ICs are mounted correctly.Boundary scan testing 

requires that all the ICs to be tested use a standard test configuration procedure, the most common 

one being the Joint Test Action Group (JTAG) standard.TheJTAGtest architecture provides a means 

to test interconnects between integrated circuits on a board without using physical test probes.

JTAGtool vendors provide various types of stimulus and sophisticated algorithms, not only to 

detect the failing nets, but also to isolate the faults to specific nets, devices, and pins.

When boards fail the test, technicians maydesolderand replace failed components, a task 

known asrework