Hi John- First, I do not have first hand experience so my input is pure theory. This type of package (in Some Cases) has a center grounding bonds and leadless legs ups the difficulty tremendously. With no stand-off from the Balls(or Legs) when the solder paste collapses during reflow the chances of shorting increases. My feel is they resist doing this type of package as 1) it is difficult and 2) it adds extra steps into the process i.e. Xray. You have to have awesome process control with this component.
I am sure some of the gurus can provide more insight.
Cal Driscoll Communications Test Design, Inc www.ctdi.com
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