Flex circuits can run 10+Gb/s signals, but many factors need to be met.

Can flex circuit boards run 10+Gb/s signals? Answer: Multiple factors must be juggled to successfully run signals that are 1Gb/s and above on flexible circuitry. I will address each of them individually.

Controlled impedance. Just like any high-speed rigid PCB, a successful high-speed flex design will have to incorporate a target characteristic impedance. To do so, match the characteristic impedance of the flex to the rest of the system to ensure minimal reflections and crosstalk. This can have negative consequences for mechanical performance, however. Elevated impedance requirements typically equate to thicker dielectrics, thereby making the circuit much less flexible.

The impedance value of a circuit is driven primarily by the signal trace width, the layer-to-layer spacing between signal trace and reference plane, and the dielectric constant (Dk) of the insulating material between the signal and plane. For most flexible-circuit manufacturers, yields start to drop when trace widths fall much below 0.003" (0.0762mm), so any significant trace width reduction beyond that can have a hefty cost impact. Also, traces under 0.005" are fragile and may develop cracks in tight bend-radius applications.

Is it the mask, or is it the gold-plating underneath?

Peelable masking has been used in the past to protect gold key pads during soldering or from solder spitting during reflow, which leads to solder wetting spots on some terminals. This, in turn, may be a cosmetic issue, but also may affect the operation of the contacts.

In FIGURE 1, the peelable coating reflects poor adhesion of the gold to the surface of the pads. This problem is related to the preparation of the contact pads prior to gold or nickel plating and was not related to the assembly process or mask. Testing for gold adhesion using IPC methods showed a total lack of adhesion of the plating.

Whether round or rectangle, HDI will be required to meet the needs of next-generation semiconductor nodes.

Can the electronics industry influence global trade pacts with China? And should it? The word from many major trade groups appears to be “yes” and “maybe not.”

IPC, SEMI, the Semiconductor Industry Association and National Association of Manufacturers have each commented of late on the proposed tax hikes to be levied by the US on Chinese imports in response to concerns over China’s technology transfer policies and the massive trade imbalance between the world’s two largest economies.