It’s Worth Revisiting Co-Planarity
Maybe you haven’t been paying too much attention to co-planarity. But the fact of the matter is it is a moving target. And it’s not moving at the usual rate as before. Now, with the advanced technologies OEMs are adopting on their PCBs, co-planarity is definitely and rapidly escalating to new levels and like the old saying goes, ‘it’s taking on new meaning.’
Consider that BGA and micro BGAs, CSPs and micro CSPs and the ultra-fine pitch they’re introducing demand that you make a careful evaluation of board surface finishes. Also, among the other major issues associated with the newer co-planarity there is BGA placement, stencil design, and last, but not least, thereís the PCB design itself. The bottom line is you’ve got to have an amazingly perfect board surface to assemble BGA and micro BGA devices on a PCB.
Check out our SMT Article on co-planarity by clicking on http://www.smtonline.com/pages/zone.cgi?a=83394&artpg=1&topic=0 to get more detail on this critical subject.
In the meantime, here are some tips and hints to help you move to the next level of co-planarity.
- Make sure your PCB assembler has the most accurate pick and place system on their SMT line.
- Find out if BGA balls on your PCB require more solder paste compared to other components, as shown in the figure. This creates a cold solder at that joint, leading to a BGA intermittent connection and subsequent field defect or failure.
- Don’t get overly complacent with HASL; it may not be suitable for you now.
- Get acquainted with ENIG/electroless-nickel immersion gold and OSP/organic solder preservative. They may be better surface finishes for your boards.
- If your PCB assembler canít figure out why your PCB has incurred warpage, tell them to check on the design of the ground and power plane stack up and copper distribution on the boardís surface.
- Find out how much experience your PCB assembler has as far as designing perfect stencils.
These tips and hints as well as our SMT article barely cover the tip of this iceberg. There’s considerably more to learn to take precautions against encountering issues dealing with co-planarity. It’s always a good idea to closely work with an experienced contract manufacturer or EMS provider and heed their advice. These are the skilled engineers and technicians who daily work with advanced PCB technologies and may have already resolved many of the issues you haven’t considered.