Page 58 Continued from previous page
except in the QFN area inside the solder mask where it is 0.01mm thick. In this case the mask opening was of the order of 0.125mm per side except on the ends of the pad rows where it was less. There are several limitations to this approach. First, the spacing between the step and the solder mask is extremely small allowing for little misregistration. Also, the stencil is thinner for all other components except the QFNs, which may yield insufficient paste. The first limitation could be addressed at the PCB design level by making the mask-to-pad clearance much larger, of the order of 0.25mm
www.us-tech.com Stencil Printing Challenges
per side, as well as leaving the ground plane without any solder mask surrounding.
Stencil without a Step Another possible solution is a
single level stencil without step, but with nanocoating on the aperture walls as well as on the bottom (PCB) side of the stencil. Nano coatings have a property called fluxophobici- ty. Quite simply, it is the stencil’s ability to resist the spread of flux on its surface. It is measured in the form of the “flux contact angle”. This is the angle that the flux will form when a drop is placed on the surface of the stencil. Nanocoating not only increases the paste’s ability to
release from the apertures, but also to resist spreading on the bottom side of the stencil when the paste is
May/June, 2012
Step electroform stencil on PCB side, 0.1mm thick around QFN apertures and 0.08mm elsewhere for all other apertures.
extruded into a cavity created by the NSMD-Window. This property not only eliminates the need for frequent under-board wiping, but also reduces the occurrences of pad-to-pad bridg- ing. Stencil design for micro BGAs depends on the solder mask design on the PCB. For non-solder mask pads overprinting is recommended. For example, for a 0.3mm pitch µBGA with a 0.2mm pad and a 0.25mm mask, overprinting with a 0.175 aperture is recommended. For a 0.100mm stencil thickness, the area ratio for this configuration is 0.43. For a 0.075mm stencil thick- ness the area ratio is 0.58. A 0.100mm thick stencil would require an electroformed stencil with nanocoat, whereas a 0.075mm thick stencil would require an electroform or a NicAlloy with nanocoat. Although QFN and µBGA
We’ve forged the path …
for your product’s success.
devices present a challenge to the SMT assembly process, with proper stencil design, proper stencil technol- ogy selection, and proper PCB solder mask layout these challenges can be overcome.
Contact: Photo Stencil, 4725
Centennial Blvd., Colorado Springs, CO 80919 % 719-599-4305 fax: 719-599-4334 Web:
www.photostencil.com r
Testing for Counterfeit Components
Continued from page 52
for testing electronic components. There are five industrial cate-
gories for testing components: com- mercial, industrial, automotive, mil- itary/aerospace and space.
Commercial. Perform DC, AC func- tional and parametric testing over the temperature range of 0 to +70°C.
Industrial. Perform DC, AC func- tional and parametric testing over the temperature range of -40 to +85°C.
Automotive. Perform DC, AC func- tional and parametric testing over the temperature range of -45 to +110°C.
Boundary-scan defined
Algorithm innovations for test and ISP
Integrated production test solutions
Testing of advanced digital networks
Technology fuels our passion Boundary-scan at its best.
Technology fuels our passion for innovation. Turn to us for advanced solutions in test and programming.
www.jtag.com 4:01:55 PM
Automated, rapid test development
Visualization to “see” boundary-scan
Military and aerospace. Subgroups 1, 2, 3, 4, 5, 6, 7, 8A, 8B, 9, 10, 11 over the temperature range of -55 to +125°C.
Space. Subgroups 1, 2, 3, 4, 5, 6, 7, 8A, 8B, 9, 10, 11 over the tempera- ture range of -65 to +150°C.
After testing electronics compo-
nents for over 30 years, we have found that by exercising the proper testing methodologies, the electronics indus- try can have more confidence in the performance and distribution of these products. When performed correctly, proper electrical testing provides a more thorough exercise in analyzing performance accuracy thereby ensur- ing risk mitigation. Counterfeit electronic compo-
nents continue to become more sophisticated and therefore harder to detect. Some of the more recent component testing instruments can be fooled by sophisticated cloned or counterfeit components. It often takes sophisticated and thorough testing to spot a fake. Contact: NJ Micro Electronic
Testing, 1240 Main Avenue, Clifton, NJ 07011 % 973-546-5393 Web:
www.njmetmtl.com r
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