CircuiTree - December 2008 - (Page 20) Is Your Solder Mask Process Ready for the Fine Pitches? Anders Ekman Component Technology and Miniaturization Component technology and assembly have historically been driving new material developments to meet requirements for solder mask materials and application processes. The requirements for smaller component pitches with advanced functionalities have rapidly increased in the past few years. There is a continuous request for miniaturization Figure 1 Possible 0.4/0.3 mm BGA Designs Reduce Solder Mask Clearances Down to 20 μm Depending on Pad Sizes 20 December 2008 • circuitree.com of electronic designs, especially in consumer handheld electronics, where the component pitches are reduced to the minimum. The solder mask material has to be able to form smaller features on the surface combined with high registration and imaging accuracy on large production panels. Fine pitch designs from 0.4 mm are in volume production while 0.3 mm has been tested and will be introduced in the next few years. The PCB producer needs to be able to process large production panels with fine pitch designs in both outer layer and solder mask HDI production processes. So far this has been possible with standard contact printing equipment using optical registration technology. For the nextgeneration components this will be extremely challenging and it will be difficult to achieve acceptable production yields. Depending on pad size designs, solder mask clearances are down to 20 µm, with small features of 50 µm between pads (see Figure 1). LDI Imaging Technology LDI imaging technology was introduced in PCB manufacturing some years ago. PCB producers started to introduce the LDI imaging process to improve the registration accuracy in the production of inner and outer layers. There are a number of compatible resists available for LDI primary imaging where dry films are the most Figure 2 LDI Solder Mask Processes Emerging in Global PCB Market 22 http://www.circuitree.com
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