9 Reasons to Consider a Solder-Down SoM

The scale of hardware and firmware tasks required to integrate the latest 64-bit ARM-processor SoCs is growing ever larger. So the majority of projects are turning to system-on-modules to boost project timescales, reduce complexity, and enable project teams to focus on their core competencies.

Traditionally, SODIMM, or push-connector modules have been a standard, but solder-down SoMs are quickly taking hold. What are the advantages (and pitfalls), and when should you consider moving to a solder-down module?

Solder-down SoM Advantages

  1. Smaller. As pressures on miniaturization grow, even at 7cm (2.8”) x 4cm (1.6”) ( (including the connector), a SODIMM module costs space, and this can matter. The smallest solder-down modules are as little as 27mm (1.1”) square. A much lower profile too – can be under 2.5mm (0.1”). That’s a smaller space that you would manage to fit the basic components on your own board.
  2. No connector. Obvious, but what really matters is the cost associated with the connector. Even a SODIMM200 connector can cost a couple of bucks, which eats into the BOM cost, and push-fit connectors can be much more, plus any mating connector on the module is also being paid for.
  3. More rugged. Soldered-down components are less vulnerable to shock and vibration

    27mm square i.MX8 QFN Module

  4. Easier routing. Most solder-down modules incorporate a ground-plane back. As long as the I/O is presented at the edge, on paired contacts, high-speed differential signals can be easily routed out on a single layer. 2-layer baseboards can be possible.
  5. Better for EMC. The ground plane provides a defined return path, avoiding ground loops and permitting crossing-free routing. In tandem with assisting differential pair routing this makes it easier to produce a low EMI baseboard PCB.
  6. Thermally efficient. The ground-plane aids transmission of heat to the baseboard, reducing the need for heatsinks.
  7. Easy Soldering. Some solder-down modules are specifically designed to use surface-tension effects to self-position during reflow.
  8. High-speed Assembly. Supplied on tape-and-reel ready to install on the pick-and-place machine feeder, solder-down modules can be used like any other component, and don’t have to be manually handled and inserted like a SODIMM.

    Rear with segmented ground plane

  9. Lower price. Solder-down modules are often less expensive than their SODIMM counterpart, because they are easier to handle and test in manufacture, and allow better economy of scale.

And here are 5 pitfalls and potential disadvantages to think about and avoid!

  1. Larger packages can warp. Ask any SMT production manager how they feel about large (>30mm) packages and sub-boards. Microscopic warping during reflow can cause poor connections, so solder-down modules should not get too large.
  2. BGA designs can be problematic. BGAs are great for density, but they need to sit, very precisely, on their bumps. Any issues and X-Ray is the only way to see what is going on under the package. Edge-contact SoMs are better as you can actually see the connections.
  3. 2-sided designs may store up problems. All SMT components are designed to pass through reflow twice. If a module has components on the back, they will pass through reflow 3 times, causing potential failures and warranty invalidation. Stick to single sided modules.
  4. Think programming! Unlike a SODIMM, you can’t program the module at a station before soldering it onto the board, it’s not practical to do that. So make sure you have a strategy from the start to allow programming in situ. Most modules will ship with a bootloader pre-programmed.
  5. Plan for field updating. Remember you no longer have the fallback option of swapping modules in the field. You need to have a cast iron strategy for remote updating, perhaps via OTA updates.

SODIMM modules are certainly here to stay, especially for smaller volume projects. But for larger volume manufacture, it looks like solder-down modules are the future! Direct Insight is here to help  – you can see our range of solder-down modules here.