Fusion or Direct bonding is a unique lamination process for multilayer PCBs that bonds the layers together without the aid of any pre-preg or bond ply. This is accomplished through the exclusive use of Teflon/PTFE material that has self-bonding properties when subjected to pressure and very high-temperatures in a very lengthily and tightly controlled lamination cycle.
High Performance Materials like PTFE/Teflon are gaining popularity due to the ever-increasing demands of RF/Microwave related products to have a consistent DK, Low DF, tight thickness tolerances and greater needs for thermal control. While Hybrid and FEP construction offer heightened performance, Fusion Bonding offers the highest performing solution in all areas and is the only option that offers a homogenous DK.
“Understandably, many manufactures don’t want to take on the challenge!”, says Transline Technology VP of Engineering, Larry Padmani. “First of all, you need a lamination press that far exceeds the available temperatures of a standard lamination press. Secondly, the cycle for fusion bonding is very long and can tie up your presses for large portions of your manufacturing day.”
Mr. Padmani acknowledged that “recipes” for fusion bonding are widely available (in the form of lamination profile charts) from major material suppliers, like Rogers, Corp. When asked why, then, aren’t more PCB fabricators attempting fusion bonding, he stated that even with the profiles, the process requires a bit of finesse to fine-tune the process. “So”, stated Mr. Padmani, “the profiles, while very helpful, are merely a jumping-off point to create a facility-specific ‘working’ profile. PTFE/Teflon material is very expensive to experiment with!”, he said grimacing, “Then, once the process is sound, we must thoroughly train our press operators in such a way that the desired result is both sound and repeatable.”
While developing this process, at TTI’s 20,000 Square Foot Facility near Disneyland, the Rogers Corp. Application Development Team and Lab worked closely with Transline to aid in their success. Afterwards, Rogers took the fusion bonded samples into their lab to perform cross sections that affirmed Transline’s success. In the photographs of the cross sections a, barely detectable, secure bond line can be seen along with fully encapsulated inner layer copper features.
Customers like Lockheed Martin Aeronautics were the motivating force for Transline to develop the capability to do fusion bonding. LM’s Advanced Product Development Division (ADP), otherwise known as “Skunk Works,” is consistently pushing the envelope of current technology limits. Transline credits Skunk Works engineers and their driving innovation with their success with Fusion Bonding along with many other processes that have set Transline apart from other US fabricators. Fusion bonding is not yet widely used due to increased material and labor costs, but the request for it seems to be growing. More often, Transline sees Hybrid construction and some FEP construction to increase perfomance. While Transline builds many digital, low layer count boards, approximately 60% of their total current business in the higher performing RF/Microwave markets.
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TTI is a world class manufacturer of rigid, high mix, printed circuit boards. We specialize in RF and high performance PCBs which accounts for about 60% of our business. TTI is ISO 9001 certified, ITAR Reg, IPC, ROHS compliant and SDB 8(a) certified.