Design had to be fan-less
In an ordinary computer, the heat generated by the CPU is not a design challenge. If the specifications include palmtop operation, however, as with the handy CF-U1, ingenuity is required to make sure that the bottom of the casing, where the device comes into contact with the hand, stays less hot.
The usual means of cooling using a fan brings more size and weight.. Clearly, the CF-U1 had to be fan-less.
Even so, rejecting the use of a fan could be allowed to compromise performance. While securing the highest possible performance, we had to make sure that the heat generated by the CPU is hard to be transferred to the user. Here, Panasonic came up with innovative solutions. As a result, it was possible to ensure that the external surface of the fan-less CF-U1 remains cooler than the casings of comparable fan-cooled models made by other companies.
Heat-efficient CPU selected, then ingenuity applied in two different ways
First of all, in the Intel® Atom™, we selected an energy-efficient, high-performance CPU that was specially developed for handy devices. The Atom™ very well balances modest power needs and performance.
For the ultra mobile CF-U1, however, Panasonic came up with two innovations to ensure it could perform to the max and become the handheld computer that everyone would want to use.
One innovation involved getting heat away from the CPU with a special heat sink design and, in the small body of the CF-U1, the other was to provide an internal air space as insulation from the heat generated by the CPU.
Magnesium alloy frame also doubles as heat sink
In a sealed unit, the heat generated by the CPU has to pass from the PCB to the body and be released to the outside of the unit. To do this, while efficient heat transmission is necessary, it is also important to prevent the heat from concentrating in hot spots on the surface of the unit. In particular, as far as possible, heat should be kept away from any part that the user has to remain in contact with during operation.
In the CF-U1, the main PCB is sandwiched in a magnesium alloy frame (Magnesium Holder), which both efficiently conducts heat away from the CPU and chipset, and allows the heat to be evenly radiated from the upper frame. If the only consideration were thermal conductivity, because copper transmits heat better than magnesium alloy, it would be better to use a copper heat sink. But, in addition to the original purpose of bracing the PCB, the entire inner frame of the CF-U1 is designed to function as a heat sink. To keep down weight and resolve the thermal dissipation issue, a rational design decision was made to use it in this double role.
Air space dissipates heat and insulates the lower surface of the case
Now, let’s look at the lower casing, where your hand actually comes into contact with the CF-U1.
The working heart of the CF-U1 is the main PCB, sandwiched in a magnesium alloy frame (Magnesium Holder). Between this and the bottom part of the unit, the lower case, there is a gap on 00 mm. This creates a layer of air. Because heat does not travel easily through air, this air space effectively provides a layer of insulation. Thus, heat that has been conducted away from the CPU by the magnesium alloy frame is not directly transmitted to the body of the unit. Moreover, in the air space, thermal convection evenly distributes the heat and no hot spots form on the bottom casing. As a result, when the CF-U1 is operated as a palmtop, even on a bare hand, it does not feel hot partially to the touch.
In addition, the thickness of the plastic in the lower case is optimized to ensure that the surface temperature remains low.
Heat protector for long periods of comfortable hand-held operation
The CF-U1 is available with a built-in wireless WAN option. Use of high-frequency communications, however, uses a lot of power, and more power means more heat. To protect users from uncomfortable heat buildup, the back of the WAN module is covered by a heat protector.
The heat protector is not simply a single layer of plastic applied to the WAN module.
If you look at the surface of the heat protector you will notice two parallel ridges. These two ridges are on the side facing the CF-U1 PCB and ensure a small gap of about 1 mm. Even such a small space provides the same kind of air insulation that is already incorporated in the CF-U1 design, and acts as a barrier to the heat generated by the WAN module.
It would also be possible to use a layer of insulating material, but such materials in a 1 mm thickness do not provide much of a thermal barrier. In fact, because air is so effective at preventing the direct transmission of heat, it is better not to fill the space.
The challenge was to achieve a compact design while at the same time ensuring heat could be dispersed without a fan. By incorporating an internal air space and making maximum use of structural parts, it proved possible to come up with a handy product that does not feel hot to the touch.