Updates in IPC-6018B help engineers design high-reliability boards specification addresses growing field of microwave technology
Written by dburford
Thursday, 03 May 2012 20:36
As printed boards evolve and chip speeds increase, the use of microwave technology in commercial applications, such as cell phone towers and in military products, is expanding. Printed boards that incorporate high speed chips and microwave circuitry have many parameters that are quite different from more mainstream rigid and flexible printed boards. These differences are covered in the “B” revision of IPC-6018, Qualification and Performance Specification for High Frequency (Microwave) Printed Boards, and the changes to the specification are extensive.
According to Michael Luke, chair of the IPC-D22 High Speed/High Frequency Board Performance Subcommittee that developed IPC-6018B, microwave boards are often made with polytetrafluoroethylene (PTFE) materials. These laminates have distinctive properties when layered together. For example, drilling microwave boards made with PTFE can often leave behind resin debris or “resin smear.” This is a big issue that Luke says is addressed in the revised document by providing specific criteria for the allowance of resin smear.
In addition, references to embedded passive resistors and capacitors have been included within the specification. “This version also better defines hole breakout requirements that occur when holes aren’t drilled in the center of a pad.” “Thermal stress” criteria have also been revised to address advances in the convection reflow process for thermal stressing of microsections or production printed board samples. “Now we have three techniques for subjecting product to thermal stress for evaluation and acceptance. In the past, there was only one. We’ve also added two new reflow profiles,” explains Luke.
The specification also expands the types of finishes that can be used. Electroless nickel/electroless palladium/immersion gold (ENEPIG), immersion silver and immersion tin are just a few examples.
The B revision includes new requirements for procurement selection, copper wrap/cap plating of filled holes, laminate cracks and voids and etchback. In addition, at the end of the document, a table for inspection criterion has been updated and an appendix for the space and avionics industries which have tighter requirements has been added.
IPC-6018B is available for purchase by IPC members for $46. The standard industry price is $93. www.ipc.org/6018