Dual layer, single sided Aluminum PCB - Page 1
Forum section: electronics / general

author: elektrinis
author_rank: Regular Contributor
timestamp: May 10, 2018, 08:21:07 am
content: I have this power electronics project which contains a bunch of mosfets and several complex chips (64+ pins) with power pads etc. Due to various constraints, aluminum PCB would be ideal.I have looked around various websites for "online quote" and could only find single layer aluminum PCBs. I know that more layers are possible, up to 4 or even 8, but could not find any with online quote. For this to work I need a minimum of 2 layers (same side).I understand this is bit of less-mainstream product, but wondering if it is possible to get a quick quote online. I want it online mainly to save on cost (as manually estimated project will be much more expensive), also to save weeks of chinglish chats.So, is there any supplier that I can use?My alternative would be to do a single layer aluminum PCB for mosfets and then add another FR4 board on top, but let's call it Plan B for the moment.

author: DC1MC
author_rank: Super Contributor
timestamp: May 10, 2018, 08:48:43 am
content: http://www.amitroncorp.com/printed-circuit-boards/aluminum.html

author: DerekG
author_rank: Frequent Contributor
timestamp: May 10, 2018, 03:12:34 pm
content: Quote from: elektrinis on May 10, 2018, 08:21:07 amI went though this same exercise last year.In the end, the most economic solution for us was to change to through hole mosfets which were mounted onto a copper heatsink that was installed 4mm above the circuit board.Just thinking outside the square.

author: elektrinis
author_rank: Regular Contributor
timestamp: May 10, 2018, 03:26:18 pm
content: Quote from: DerekG on May 10, 2018, 03:12:34 pmInteresting thought, thank you for sharing. I was wondering why virtually all chinese power electronics (eg. ebike controllers) come with TO220 fets and many passive PTH components.It looks very labor-intensive: if a PCB house is used, first you have to make a template and provide it to them to solder the fets on it so they would fit in to tapped holes during mechanical assembly. Then, once received assembled board, apply silicone grease, add insulators and insulating washers and bolts and hope for best. Or have your mechanical assembler to solder the fets once assembling everything, which is also a very finicky procedure with a great room for error and static shock.I was going to make a full SMD solution to avoid as much manual assembly as possible.Hard to believe all that TO220-related assembly is cheaper. Ming boggles.Do you remember any numbers behind the reasoning to go with through hole design?So far I see that 100x100 mm aluminum board (single layer) goes for 1-2 bucks @100 pcs. Definitely not 10 cents, but if it's thick enough, you save on heatsink..

author: DerekG
author_rank: Frequent Contributor
timestamp: May 10, 2018, 04:06:09 pm
content: Quote from: elektrinis on May 10, 2018, 03:26:18 pmOur boards are 130mm x 100mm, so going Al substrate was not cheap.The heat dissipation area on a TO-220 or TOP3 or TO247 is much larger than a D2 package or similar. Therefore we were able to save quite a lot on mosfet costs by choosing a higher Rds through hole part.We have 4 mosfets per board.. The legs of the mosfets are bent 90 degrees so that the flat copper plate heatsink needs no other mounting hardware. This speeds up assembly.The copper heatsink is raised 4mm above a standard 2oz FR4 PCB. This allows some low profile SMD components to sit beneath it, but at the same time gives us sufficient clearance to run the copper heatsink at 250V DC. No insulation washers etc are therefore required for the mosfets, just a screw, nut, spring washer & heatsink compound. Ohhh ..... and a little fingernail polish to prevent the screw from coming loose.For the Chinese, labour is cheap but parts are expensive. Our original D2 pack mosfets cost about AUD$8 ea whereas the through hole TO-247 parts are in the mid AUD$4 range. The copper plate we use as a heatsink runs in at about AUD$1.50 compared to a much less efficient aluminium heatsink that costs about AUD$0.60By moving to a copper heatsink we could increase the power we push from 2.8kW to 3.6kW. In SMD we could not push more than approx 2.4kW without running into thermal issues (which is why I started to look at aluminium substrate PCBs).I started a thread on EEVBlog last year asking for suggestions re this project & another kind reader suggested moving the heatsink from aluminium to copper. I am indebted to him for a simple but very effective solution.

author: elektrinis
author_rank: Regular Contributor
timestamp: May 10, 2018, 04:17:44 pm
content: thanks for your in-depth response. Looked in to copper and it is indeed much better for spreading heat area. Looks like there are copper-based boards as well, but I'm not sure I want to know the price.In my case insulation will be needed, so that complicates things a little. I also saw this technique that you are describing used by several higher end ebike controllers as well. Some of them have even omitted bolts entirely by placing a single sheet of silicone insulator and then pressing down the PCB with couple bolts. PCB flexes etc, but probably is good enough in some applications.Tried to find your thread, but forum search provides too many hits...

author: DerekG
author_rank: Frequent Contributor
timestamp: May 11, 2018, 11:56:52 am
content: Quote from: elektrinis on May 10, 2018, 04:17:44 pmYes, there are even double sided sticky pads (like double sided tape) that are designed to suck away the heat.I've even seen pop rivets used to affix TO-220 etc to the heatsink.Nothing beats the manufacturers recommendations to use heatsink compound and a screw & nut!QuoteFound it for you:https://www.eevblog.com/forum/manufacture/soldering-mosfets-directly-to-aluminium-plate/

author: elektrinis
author_rank: Regular Contributor
timestamp: May 11, 2018, 01:09:11 pm
content: Thanks a lot.P.S. If someone comes up with a link to dual layer aluminum pcb, feel free to share.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 26, 2018, 03:23:41 am
content: Aluminimum substrate seems to be called "IMS", (Insulated Metal Substrate).This manufacturer has a calculator, but has european prices, not Chinese."European prices" seems reasonable if you need 100+ pcb's or so.But they do not seem to do double sided Aluminimum.https://www.eurocircuits.com/IMS-pool-orderpooling-for-Insulated-Metal-Substrate-boards/The problem with doulble sided Alu. is that that stuff is conductive.It is very hard to put via's through it without shorting stuff.But it does seem possible:https://www.multi-circuit-boards.eu/en/products/printed-circuit-boards/metal-core-pcb.htmlSome time ago I bouth a few stepper motor drivers ( Wantai DQ542MA).They used TO220 THT with the "tabs up".Put 4 holes / screws through the PCB to fixate a piece of aluminimum to 8 transistors.Quite a neat way of fixing some cooling to your transistors.