Growing numbers of OEM products are becoming smaller to the point of micro miniaturization. Those include medical and commercial products. This emerging breed of OEM product demands PCB microelectronics assembly and especially sub-micron device placement.
The current industry standard for accuracy for placement of MEMS devices, sensors, bio sensors or other kinds of pressure sensors is five-micron placement accuracy on a very small rigid or rigid-flex board. If you place a die on a tiny circuit board, it will be placed with plus or minus five-micron accuracy based on many die bonding machines on today’s assembly and manufacturing floors.
However, miniature devices are continually shrinking in size to the point where five-micron accuracy may not be sufficient for state-of-the-art products such as small medical insertable, implantable, or wearable products. Or, for that matter, any other miniature OEM product.
That means you have to use extremely high-end placement devices, which have less than a micron, or in other words, sub-micron placement capabilities because these devices are so sensitive. Pad sizes are so small. The wire bond attach angles are so tight that you need the wire bonds to be placed on adjacent bond pads with next to nothing tolerances available to play around with when doing these placements.
Check out our recent SMT column on sub-micron placement for a more comprehensive understand. In the meantime, here are some tips and hints to get you started.
- Check to see if your EMS provider offers device placement with sub-micron accuracy.
- If so, they should be able to quantitatively verify sub-micron accuracy.
- Also, they should be able to quantitatively prove that accuracy. A highly sophisticated digital microscope accurately measures what is being placed and verifies placement accuracy in microns. See inconsistent pad accuracy view, Fig. 1.
- They should have a backup technique to be able to verify placement accuracy such as x-ray as a secondary source.
- Tiny dies and other devices can only be accurately placed on a board with a sophisticated sub-micron die bonding system. But these same tiny dies and devices cannot be effectively assembled with standard five-micron placement machines.
- Die placement will not be optimal when the brute force method is used with five-micron placement when accuracy requirements are one to two microns or sub-micron.
As our industry moves more into micro-miniature PCBs and microelectronics assembly and manufacturing, the prudent OEM will take a closer look at the key elements of sub-micron die bonding. It’s highly important to gain a better understanding of the consequences incurred by naively taking the five-micron placement route instead of the sub-micron die bonding one.