Molex PicoBlade, yes, one of my favorite connectors thus far. Can you reflow solder the header versions of these connectors directly onto a printed circuit board? Most of these connectors are made of Nylon, which is deemed unsuitable for reflow soldering due to its high moisture absorption rate. I searched around on Digi-Key for PicoBlade headers using a different insulation material, but I’ve found nothing. So, is there other information out on the wider Internet about reflow soldering with Molex PicoBlade connectors? Yes…
20200406/DuckDuckGo molex picoblade reflow soldering
According to this Wikipedia article, many JST connectors are made of Nylon and are unsuitable for reflow soldering, though there are a few versions made of a different insulation material that will work with reflow soldering. Ah, that’s not very helpful, other than hinting that maybe it’s not possible.
20200406/https://en.wikipedia.org/wiki/JST_connector
But seriously… I’ve seen commercial electronics with Molex PicoBlade connectors positioned such that they could be coming straight out of a circuit board. And indeed, there is quite the trick here. This is a great article listing lots of information about reflow soldering, along with lots of great tips on parts selections to best prepare your designs for automated mass production manufacturing. For example, parts should have a flat surface so that they can be picked up using a standard vacuum suction pipette, thereby not requiring more specialized grippers or pipettes.
20200406/https://www.phoenixcontact.com/assets/downloads_ed/global/web_dwl_promotion/52004352_EN_HQ_Connectors_for_SMT_Production_LoRes.pdf
But, of course, the best thing that this article says is in relation to using Nylon in reflow soldering. You can, in fact, use Nylon in reflow soldering environments, it’s just that you have to pay attention to the specifics of the moisture sensitivity level. This is a quantitative specification about how much time a part can spend outside of the bag within the general factory floor space at room temperature before it has absorbed too much moisture and has to be rebaked to eliminate the moisture. Specifically, baking at 125 degrees Celsius for 4 hours.
So, here’s the key. What if you don’t know what the specific moisture sensitivity level of a component is? Apparently, moisture sensitivity level is specified clearly for many surface-mount IC packages, but connector headers tend to be devoid of such specifications. In this case, the ability to rebake components to eliminate moisture will save you. You simply assume that the component is the most sensitive moisture sensitivity level and you must rebake it before performing reflow soldering. This will eliminate all the moisture inside the component, so then you can safely subject it to the full reflow soldering temperature without risk of delamination.
In essence, this is simply like an extended pre-heat section of the reflow soldering curve. Now you really know why pre-heat is recommended during reflow soldering. Yes, it is to introduce components to a more gentle rise in temperature to avoid fractures and other breakage. However, it’s not just for temperature, it’s also to allow for a more gentle elimination of humidity in case the outer casings of components may have absorbed some moisture.
20200406/https://en.wikipedia.org/wiki/Moisture_sensitivity_level
20200406/https://en.wikipedia.org/wiki/Polyamide
20200406/https://en.wikipedia.org/wiki/Nylon_6
Also, that great resource on reflow soldering specified another great subject: reflow soldering wtih through-hole components. You can use solder paste for through-hole components. How? Push the solder paste into the through-holes so that it fills them completely and pokes out a little bit on the other side. Then, push your through-hole components into the board. There will be a little bit of excess solder paste on the bottom of the through-hole component legs. That’s okay, leave that there and try not to disturb it. Then place the board in the oven. The solder reflow will spread all the solder around the component nicely and create a meniscus of solder at the top of the board.
So, what’s the problem with using a soldering iron with solder paste and through-hole components? It’s the whole “top of board” thing. Usually, when working with a soldering iron, you work on the bottom of the board, so if you used this technique, the solder wouldn’t spread around so nicely like it does when you do the full reflow soldering technique in the oven.
By the way, through-hole components typically only make sense to place on a board single-sided because, well, when the legs must extend all the way through the board, that’s surface area that is consumed on board sides of the board to support the legs, so there isn’t much of an advantage to put such components on both sides of the board.