The need to chase the market very often forces the manufacturers of electronic systems to neglect some fundamental aspects of the quality of supply, paying attention mostly to the low price. Unfortunately, this type of approach has hidden costs which will be revealed to be significant in the mass production phase.
Furthermore, the rapid advancement of technology also makes it difficult to keep up with the times, so very often a supplier does not have time to standardize a process that already becomes obsolete, forcing it to new investments or to succumb to more financially gifted competitors.
In fact, if we look at the PCB assembly technique it has gone from the PTH of the ‘80s where a wave soldering machine and a bit of space in the garage was enough to be able to present itself as an assembler to the latest SMT technology of the 2000s and today it is increasingly difficult to be able to experiment with assembly techniques without having sophisticated assembly machinery and in-line analysis systems of the production process.
Based on our production experience, we can affirm that many of the problems related to assembly defects depend on two essential reasons:
- a) correct design of the printed circuit
- b) the efficiency of the production process
| Item | Cause | Percentage |
| 1 | Bad welding | 45% |
| 2 | Missing components | 10% |
| 3 | Wrong components | 15% |
| 4 | Broken components | 15% |
| 5 | Defective printed circuit | 5% |
1)Bad welding
First of all, the PCB designer must use standard foot prints suitable for the component that has been chosen to use and providing the right opening masks in the solder and avoiding the placing of tiny components in the shadow of the larger ones.
Avoiding holes in the solder pads is an essential condition to ensure successful soldering
Provide a Burn-Inphase for printed circuits and components from long storage in the warehouse
Use alloy solder pastes according to required surface finishing process for which the PCB was thought ,
Use alloy solder pastes recently produced and / or in any case well preserved in the warehouse.
Use printed circuit boards produced by first class suppliers, free from warping, variations in substrate
thickness and / or with defects in process contamination.
Keep work areas clean, using of Clean Area is strongly recommended
Keep under control the temperature and welting times in the welding process
Use the correct thicknesses of stencil sheets when applying the solder pastes.
2) Missing components
The more automated the process, the less this type of assembly error occurs
Usually the modern Pick & Place machines are precise and reliable and are able to inform in time when the carousel has emptied or if a component is blown away, usually it is human errors that affect the final yield of a production process, even an inadequate fastening of the PCB conveyor plays an important role in the production yield if the fingers do not fix the plate well it can vibrate during transport and go into oscillation losing blows during positioning.
If a component feeder is not well fixed in its housing ,machine fails to pick components accurately.
In any case, having an automatic optical inspection AOI system is the best remedy to identify problems of this type.
Mobile probe circuit testing techniques are very useful in identifying these types of defects.
3) Wrong components
The prevention of this type of errors passes through the establishment of an adequate and well-studied quality system which will have to provide simple and effective controls over of the whole production process phases ,where everyone can check the correctness of the previous phases and interact with each other in order to correct the error detected in the document. The control procedures must be simple and upgradable with daily experience rather than entrusted to an expert external consultant who does not live the reality of the factory.
Obviously in the case of manual assembly, any type of error among those listed above can occur randomly or systematically, visual inspection and functional testing are essential in this case.
4) Broken components
Rarely can a top quality electronic component come out of its original packaging broken. Nowadays, the major electronics brands are able to produce with zero defects at the end of the construction process. Instead, we must be aware of imitation attempts and beware of the risks of buying non-genuine parts that also exist in circulation and come from the refurbishing market because in this case there is no guarantee of operation.
Typically, during the assembly process, an electronic component is destroyed due to mechanical damage or electrostatic discharges occurring during handling operations.
Here the establishment of protected areas against ESD risks is essential although it is not enough.
In fact, most of the damage caused by ESD occurs outside the protected areas, as it is impossible to imagine a world made entirely of “fresh cheese”, when the product ends up, for example, in the reworking phase or in the hands of the warehouse worker or final transporter.
The separation of PCBs from the multiple panel also represents a very frequent cause of component breakage, it would be better to use a special equipment for the final cut of the PCBs rather than relying on
the manual snap of the board or using cutters and shears that end up breaking the electronic components arranged on the border of the pcb.
5) Defective PCB
Here, too, once again, the main recommendation for preventing assembly defects is to use first-class suppliers. Modern electronics does not admit partial results ,those manufacturers who are not adequately equipped to meet the new frontiers of this market would do better not to apply in this fascinating sector, the craftsmanship of electronics now concerns the past years.
Today’s PCB manufacturer must guarantee inside equipment such as Flying Probe ,IR test, Xray Microscope, Thermography Camera ,Visual System Inspector , AOI and so on .
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