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VOLUME -23 NUMBER 9
Publication Date: 09/1/2008
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September 2008 Issue
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Improving Inspection of Lead-Free Solder
Magnified side view showing well formed balls.
By Christian Munoz, Hirox USA
Lead-free solders are said to cause various problems, such as: lack of self-alignment, bridges, solder balls, insufficient wetting, dendrites, pits, voids and peeling of soldering land. Also, on miniaturized lands, there may occur insufficient melting of solder paste. Even though these problems have not yet been resolved, lead-free soldering technologies have already been introduced at mass production sites.
Lead-free soldering technologies have reached a level where concern regarding the quality of mass-manufactured products as well as rising costs of materials call for vast improvement in inspection capabilities.
Trying to run a mass production line when inherent problems still exist has been a root cause for many issues for manufacturers, particularly for those industrial equipment makers who have been late in adopting the lead-free solder technologies. Most of these problems basically arise from heightened packaging temperature requirements in line with higher melting points of soldering materials.
Soldering is completed when these conditions are met: solder paste is melted, temperatures of the soldering land and the parts surface are higher than the melting point of the solder paste and flux is active. At this point, three items decide the temperature profile: the apparatus (functions of reflow system); the substrates including the material quality, designs and parts; and solder characteristics (including the flux).
Inspection Determines Quality
Inspection of manufactured products to determine quality of the temperature profile and proper solder connection needs to be done with a high performance inspection system. The Hirox Digital Microscope System offers several lenses that can be used for high quality inspection. Using the Hirox MX-BGAZ lens it is possible to view the top and bottom of the BGA to determine correct solder flow and view up to the third row, to determine if there are any bridges. With the Hirox MXG-5040RZ lens it is possible to determine the flow of the flux as well as back foot inspection.
When inspecting a BGA it is important to determine that the BGA is making contact at both the top and the bottom and that the BGA itself has a circular shape. With Hirox's BGA lens there is a rotational ring that allows the angle of view to change so that it is possible to have close inspection of the top contact point of the BGA, and close inspection of the bottom contact point as well. If the connection on the top or bottom is not made, the BGA will not function properly. Whenever this contact is not made, it is clearly visible when doing a visual inspection with this BGA lens. Upon completion of visual inspection of the first row of the BGA, it is safe to assume that the other rows of the BGAs also have the proper connection. Since the first row receives the most heat during the heating process, it is the most difficult row to prevent an overly high temperature profile and therefore is the row most likely to have poor connections. If the first row has a good connection and well rounded BGAs, it is safe to assume that the other rows may also be in good condition since they would have received as much heat as the first row.
By having fiber optics attached to the lens unit, it is possible to direct your lighting from many angles, in order to view BGAs clearly. This way you can clearly see the edges of these solder balls to determine if there is a good temperature profile.
Excellent Side Views
For those areas that have solder joints in which good flux flow is important, the MXG-5040RZ allows the user to get a clear idea of the flux activation. The MXG-5040RZ has a rotational adapter, which allows excellent side inspection and an angle in which the flux is clearly shown. By having the view angle different from the direction of the light source, a reflection appears across the flux. By rotating the lens back and forth, this reflection moves across the flux, making it very clear where between the leads of a package the flux has flowed. The fact that the lens allows a side view also makes it easy to view the back foot of the solder joint to make sure that it is connected properly and inspect for any whiskers or other defects.
The high quality of the lenses and brightness of the light source result in an excellent inspection image. High resolution imaging is most important for quality control in manufacturing especially for lead-free solder-based technologies, which can be extremely fickle. The Hirox Digital Microscope System provides the most complete inspection system to improve the quality control process above and beyond current standards.
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