The Incredible Shrinking Resistor: The Advantages and Drawbacks of Ever-Smaller Components
The advantages and disadvantages of ever-shrinking components.
The advantages and disadvantages of ever-shrinking components.
In 1957’s The Incredible Shrinking Man, our hero Scott starts shrinking after passing through a mysterious fog. He continues to inevitably shrink, dealing with new and worsening challenges as the film progresses. He can’t get up the stairs, he has to avoid the cat, and he has to fight off a spider with a pin as his only weapon.
Circuit designers today are in much the same situation, forced to deal with inevitably shrinking electrical components. They’re shrinking and presenting new challenges every year, whether designers want them to or not. The best we can do is endeavor to understand and mitigate the risks while taking best advantage of the benefits.
With that in mind, here's an overview of some of the major benefits and risks associated with using smaller components.
Benefit: Smaller Overall Circuit Boards
One obvious benefit of smaller electrical components is that they permit smaller circuit boards. Whether this permits packing unbelievable functionality into your smartwatch or wireless earbuds, or enables life-saving devices like implantable pacemakers or defibrillators, smaller circuit boards are driving innovation. Some even say swallowable circuits are the future of medicine. Amazing circuit designs can fit anywhere these days.
Risk: Harder to Assemble
As components get smaller, they get harder to assemble reliably. The amount of solder paste required to mount an 01005 package resistor is literally microscopic, and controlling that can be difficult. Smaller components are more likely to be misplaced by the pick-and-place machine, knocked off the board in the oven, or come out of the reflow oven tombstoned. Advancements in technologies are constantly struggling to keep pace with shrinking components.
Benefit: Higher Density Circuit Boards
Another big benefit of smaller components is circuit density. More circuitry can fit in a square inch of PCB space than ever before. Cell phones, for example, haven’t actually gotten smaller over the last couple of decades, but the amount of circuitry and functionality packed into them has grown exponentially. Ergonomics often dictate the shape and size of a product, and higher component density on the PCB just powers more functionality in the same old space.
Risk: Testing, Reworking, and Fixing
It can be extremely difficult to rework components when they are not visible to the human eye. If you’ve ever attempted to find an 0201 resistor you misplaced on your bench or attempted to measure its resistance when you found what might be the one you lost, you know what I mean.
These days, no electronics laboratory is complete without a 3D microscope or two. At the rate components are shrinking, those won’t be luxuries for long—they’ll be necessities.
Screenshot from Androkavo's video, SMD Soldering - Smallest Package
Benefit: Lower Power Circuits Possible
With the massive increase in battery powered electronics over the last decade or two, lower power circuits are increasingly desired. Tiny components on tiny circuit boards in products like wireless earbuds or remote sensors can operate on microamps, giving some products multiple days of battery life. There is a very strong correlation between the physical size of components and circuit boards and the amount of power they require to operate.
Risk: Lower Power Circuits Required
The flip side of being able to operate on lower power is that smaller components cannot dissipate higher power. If you need to design a circuit that draws higher power, tiny components probably can’t be used. Smaller components are rated for lower power, so when tiny components are inadvertently introduced to more power than they can handle, electrical surges, or even ESD (electrostatic discharge) they can be easily destroyed.
|Package (imperial)||Power Rating (W)||Maximum Overload Voltage (V)||Mass (g/1000pieces)|
Data sourced from Panasonic
Benefit: Lower Impact from Parasitic Effects
Parasitic inductance, resistance, and capacitance effects are often a function of physical geometries. Parasitic elements are circuit elements that are not desired but are inherent in the materials that make up all electrical conductors. Smaller components have much lower parasitic effects. Because the impact of parasitic effects are much worse at high frequencies, smaller components offer significant benefits to very high-speed applications.
Risk: Tin Whiskers, etc.
Unfortunately, when parts are miniaturized, spacings between them and between their leads also tend to be shrunk. This has introduced new concerns about metallurgical problems. Metals behave in strange ways on microscopic levels. Some metals, like the tin used in many lead-free solder compounds, experience whisker growth which can cause electrical shorting.
And it’s not just theoretical. In 2005, a nuclear plant in Connecticut was shut down due to a false alarm that was caused by circuit board tin whiskers. As spacings shrink, these issues have much larger impacts.
An example of a tin whisker. Image used courtesy of NASA
Benefit: Long-Term Worldwide Material Availability
The materials that make up electronic circuit boards and components are in short supply around the world. The earth has a finite supply of them, but the amount of electronics humanity produces continues to grow each year. So one big benefit of smaller components is that they consume less of those materials. One 0402 resistor has the same mass as twenty 01005 resistors. And smaller components will become more available as they become more popular, and as assembly processes become more capable.
Components have been shrinking for 60+ years, though adoption of the next smaller size at each step has been gradual. The benefits don’t outweigh the risks until they do, you might say. For engineers, understanding both the benefits and the risks is what is important.
For more in-depth discussion of tiny components and the assembly challenges they present, see this SMTA presentation.
The Tin Whisker issue is not so much lead spacing as it is a RoHS issue. Prior to RoHS, there was very little mentioned about Tin Whiskers. It was the removal of the lead from the solder that we first saw this issue. RoHS is about getting lead and other hazardous materials out of products to protect the environment. Unfortunately, lead is a very good material for electronics manufacturing. So much so, that the majority of exceptions to the RoHS directive involve lead.