原创 Do all EEs need to know how to solder?

I just read Max the Magnificent's blog: What? EEs who do not know how to solder?

Sadly, unlike Max, I was not "shocked" or "flabbergasted" to learn that some engineers can't or don't solder. Like so many things in the modern world, hand-soldering is no longer a required skill. It's useful, and I personally think that everyone in the industry should have the skill, but it's not a requirement anymore.

Years ago, I would draw a schematic on paper, acquire the requisite parts, and test the design using solderless breadboards. Once I was confident enough to create a more durable prototype, I would get out my wire-wrap tools or soldering iron. Even when wire-wrapping, I would often need to solder a few parts down.

Soldering was inevitable and it wasn't really possible to be involved in electronics without the skill. Today, however, the situation is a quite a bit different. It is very possible, perhaps even common, for an engineer to go from idea to finished product without ever putting iron to solder.

This is not to say that problems don't crop up in the process. Some of these problems could be fixed with a hot iron, but not always. The only choice may be to re-spin the PC board and have it built by someone else. Sometimes the problems simply can't be resolved by hand and—in those cases—soldering skills will help about as much as sewing skills.

Take a common problem in the prototyping domain: an incorrect footprint on the PCB. This is probably the most frequent design issue to pop up in my world. It can have a couple of different causes:

1. Metric vs. SAE measurements: It's not just Mars Probes that have this problem.
Connectors see this one a lot. If you have only four positions on a 0.1" (2.54mm) pitch header strip and you try to use a metric 2.50mm pitch header strip... no one will care. However, if you try that with 25 positions, even good soldering skills likely won't help make it fit. You'll need a new PCB.

2. QFN vs. QFP footprints: Many newer chips, especially in these form factors, don't have pre-made land patterns in CAD software. Either a footprint has to be custom made or a similar one has to be borrowed from a pattern that's close enough. QFP (quad flatpack) land patterns look very similar to QFN (quad flatpack, no lead) land patterns, but are typically larger. Swap the two and, again, hand soldering skills may not get you anywhere.

Not long ago, I was designing in a Microchip MCP72833-AMI/MF. It's a compact LiPoly charger, requiring no more than a few resistors and capacitors. It comes in two form-factors: a 3 mm x 3 mm DFN (dual inline flatpack no leads) and a slightly larger MSOP. I picked the DFN to save PCB real estate. It wasn't until after I had PC boards in hand that I discovered the DFN isn't available in the small quantities I need. This was a bad time to discover such an issue.

Had I checked and discovered that information early in the design cycle, I would have designed in the MSOP. The land patterns are close, but not close enough that I could place the MSOP on the DFN land.

Some people might turn the chip upside down and run individual 24 gage wire from the chip legs to the PCB footprint, but with 0.5mm pitch leads, I just can't do that—despite 30 years of hand soldering experience.

3. Form factors not available: You may have designed in a BGA only to find that particular package unavailable and purchase time. Part availability in a different package won't help, nor will hand soldering skills.

Take the NXP LPC11U14 ARM processor. It comes in a 4.5mm x 4.5mm BGA, a 7mm x 7mm QFP, and a 5mm x 5mm QFN. There are two other parts in the family: LPC11U13 and LPC11U12. All three are virtually identical except for the amount of Flash memory.

The BGA would be idea for keeping things small. After completing the firmware, however, I might decide that I don't need all 32K of the Flash. The LPC11U12 only has 16K and costs less. That's fine, except the LPC11U12 doesn't come in the BGA form factor.

Hand soldering won't help in any of the three scenarios described above. Of course, there are always a few exceptions to everything. I once met a guy who has hand-soldered 01005 passive components. He's a wizard though, so that doesn't really count.

So, in summary, my personal opinion is that electronics engineers should know how to solder, but I do know that not all need to. What do you think?

Duane Benson
Marketing Manager
Screaming Circuits