Are otherwise global companies putting all their R&D eggs in one basket?

Buying cars is not what it used to be. I was recently kicking the proverbial tires in search of a new automobile. This was the 18th time I underwent this process, one I approached with mixed emotions. It’s always interesting to see what new technology, appearance and driving experience has been packed around an engine riding on four tires. Yet it’s also concerning, as the cost always triggers a rethink of my priorities and change in my expectations.

This time around, the two biggest areas of technological interest also provided the greatest areas of concern. One was the lack of familiar knobs, dials and gauges. For the seasoned driver, this can cause initial, if not ongoing, confusion while navigating heat, air conditioning, music, and all the other things cars can do. The second was the lack of a spare tire. Many cars (or their manufacturers) are being touted as so reliable, spare tires are no longer necessary. Just deploy the tire repair/inflator (if you can find it on the knob-less dashboard) and away you go.

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.