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www.us-tech.com Automatic Profiling
Complements AOI & X-ray Inspection P
By Bjorn Dahle, President, KIC
ackage on packages (PoPs), µBGAs, 01005 and smaller de- vices are becoming more com-
monplace, and this can significantly impact SMT assembly. This technol- ogy trend makes all assembly processes more difficult, especially printing and reflow, and it makes in- spection a real challenge. AOI ma- chines are not designed to inspect leads that are hidden below compo- nent bodies such as BGAs and PoP. In addition, even for the leads
that are visible to the AOI camera, there is no way for the machine to look at the solder joint microstructure to determine whether there are quality issues related to a poor soldering process. A solder joint or component could be defective or weak as a result of a multitude of process issues that include overheating, too fast or too slow ramp rates, excessive time above liquiduous, and oxidization. Unfortunately, X-ray inspection
is not capable of handling these situa- tions. While this type of inspection
cannot look inside the solder to deter- mine whether it is “healthy”. Another limitation with X-ray is that most fac- tories use batch X-ray systems rather
mined whether they had been processed in accordance within both the component as well as the solder paste’s thermal tolerances. The com-
But is not profiling suffering
from the same issue as batch X-ray in that the batch x-ray does not pro- vide 100 percent inspection? Manual profiling is a spot-check operation. Many companies will profile only once a day or once a week. There are, however, numerous automatic profil- ing systems on the market that pro- file each and every PCB on the fly without interrupting the production flow. Automatic profiling systems can work together with AOI and X- ray systems for a total inspection so- lution that plugs the loopholes that currently exist, in which defects or latent defects can slip through and end up failing later on, after it is in the end user’s hands.
Tiny Leads Miniaturization of components Profiling system is essential to consistent production.
than inline inspection systems. In this case, the vast majority of the PCBs do not get X-rayed and, there-
Ultra-miniaturization of electronic components raises problems of consistency in manufacturing, greatly helped by ongoing profiling.
has the advantage of seeing through the BGA and PoP component bodies to the solder joints below, it has a sim- ilar limitation to the AOI; although it can verify things like the presence of solder balls and other solder joints, it
fore, can slip by unnoticed. However, a solution exists.
Profiling Aids Inspection When profiling these BGA and
PoP components, it can be deter-
bination of thermal profiling and AOI/X-ray inspection provides a very complete inspection process, even for the very tiny devices. In addition, the suspect PCBs that have been processed outside of the thermal process window can be rerouted to the batch X-ray station. This can pro- vide for a more effective sampling of PCBs to be inspected compared to the random sampling that is so often used today. Thermal profiling simply makes the existing inspection sys- tems in the factory work far better than in the past.
means that there are now a growing number of components that have such tiny leads that the stencil print- er deposits a very small amount of solder paste on the pads. These de- posits have a much larger ratio of surface to volume than what we have been accustomed to. This creates challenges for both the printing and reflow process. During the reflow process, one
of several challenges is that the flux may burn off prematurely and, hence, problems with oxidization will occur. The soak phase may need to be reduced or eliminated to avoid this. Continued on next page
February, 2013
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