Special esay-to-solder footprint for SON5x6mm FETs? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: July 20, 2024, 05:55:37 pm
content: Hi,We are doing a prototype board with a 24v to 15v, 3A Synch Buck on it (220kHz).The FETs are CSD18531Q5A and they are SON5x6mm footprints.CSD18531Q5Ahttps://www.ti.com/lit/ds/symlink/csd18531q5a.pdf?ts=1721491946902&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FCSD18531Q5A%253Fbm-verify%253DAAQAAAAJ_____39BV-IElTwWi7lMamknLfHczRztZfteKv7y-UiahjMgWuXR8c8Xna5pLwdl5RSq0vapDeCn1DGBnt7DWqgMYE9EQ1fTFuVp94tSQR2XIRMNJ6eQK0usDnn_Y-r1UXoRNbZtjsr8uTKdvahXFVAG8wxnn661nG5dbyXJu5wQ35zvFi0pItAScRvWXyBpyA5k64Si-6b9Pu9g34xtSNH2JBssAdHG3WH9MvN4uKl61ib3dGcfiUWOzU8P1mkpZhGdWi8FL85xhKyYw3wjwZXoJ_AtxaniOS1jHCjH_3k0eJSAVQJ9Vxawgwwx3G8zc_JuDrYOVpW4PNVN7HJFaMc3IlRmS1KpvQNqIn order that we can hand solder these proto boards easily, we have done theFET footprints asattached.The FET courtyard is the inner purple rectangle, centred on the shown centre point.So we can wet the underpad (drain) by just pressing two soldertips on each side on the bit of the underpadthat extends outside the perimeter of the FET case. This will ensure a wellsoldered underpad, without needing to use hot airor hot plate.Also, we simply extend the small source and gate pads beyond the componentperimeter so thatwe can easily solder those too.What do you think?....isn't this a great way to do the actual pads on the productionboards aswell?

author: jc101
author_rank: Frequent Contributor
timestamp: July 20, 2024, 08:57:34 pm
content: What is wrong with hot air, a hot plate, or even a small reflow oven?I've hand-assembled many boards with several of that exact same MOSFET on them.I use a small batch reflow oven, which does the whole board in one go—so much faster than trying to hand solder individual parts. It's also better quality.I used hot air from time to time, too.I never bothered to hand-solder them; there is little point in wasting time as everything else is reflowed. You will never know how well the joint is under the part unless you X-Ray it.But, no doubt, as you seem determined to do everything in the most awkward and time-consuming way possible, good luck.

author: Smokey
author_rank: Super Contributor
timestamp: July 20, 2024, 09:11:06 pm
content: PSA:EEVSewer Faringdon Alert. The reason this appears to be a stupid question is because this dude is a troll. Only reason to respond is if you want a free "thanks".Carry on.

author: floobydust
author_rank: Super Contributor
timestamp: July 20, 2024, 09:32:15 pm
content: Uhh Beavis, how about the soldermask how does it look. And why are the outside pins bigger than the inside. Who needs thermal via's.I thought he needed some new soldering irons first? Defo disorganized troll.

author: Faringdon
author_rank: Super Contributor
timestamp: July 21, 2024, 03:49:00 pm
content: QuoteThanks, For a proto board, its going to be easier to just solder it like explained in the top post?Hot plate...cant do as components both sides.Hot air...will blow off other components.We may want to desolder it and put a different 5x6mm fet on...so if we can just do it with solder irons then it will be quicker.Also, a small reflow oven instead of doing it the way of post 1.....it would be extra expense.Squirting out all the solder paste out of the stencil makes solder ovens a long job.This is treating the soldering like as a DPAK..and you wouldnt bother with hot air/oven etc with a DPAK.QuoteSo its easier to solder the gate without shorting to the adjacent source.QuoteThanks, we can still add thermal vias.

author: jc101
author_rank: Frequent Contributor
timestamp: July 21, 2024, 03:58:47 pm
content: Quote from: Faringdon on July 21, 2024, 03:49:00 pmPerhaps some time spent learning how to use hot air would pay dividends. It's way easier than needing two people to do the job: one person holding the irons and another holding/removing the part.A double-sided load should be no problem for reflow. If you think it is, you've designed a board that cannot be put into production.This thread could be an example of generating a design based on wanting to use the wrong tool for the job.Have fun.

author: Faringdon
author_rank: Super Contributor
timestamp: July 21, 2024, 05:31:48 pm
content: QuoteThanks, but dont need two people, the two irons get used as like chopsticks, once its got hot enough.Out of interest, how do you solder/desolder DPAKs?.....i am just applying that kind of thing to the SON5x6mm.A DPAK is easy, so make the SON5X6mm technique like the DPAK technique.

author: jc101
author_rank: Frequent Contributor
timestamp: July 21, 2024, 05:50:07 pm
content: I primarily use a reflow oven and hot air if parts need to be replaced. Swapping such a part takes maybe a couple of minutes, with no damage to the PCB or parts.I'm impressed you can uniformly heat a large drain area (more so if there is a decent heat sink area and thermal vias), plus the gate and source, sufficiently evenly for clean placement/removal with one hand and two irons.Post a video of that so others can see the technique.