LeafLabs Garden » Topic: State of the Leaf?

LeafLabs Garden » Topic: State of the Leaf? http://forums.leaflabs.com/topic.php?id=1204 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:08:16 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php siy on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=3#post-7525 Sun, 08 Jan 2012 06:40:27 +0000 siy 7525@http://forums.leaflabs.com/ Thanks for the info about films. As for chemicals, I'll find details by myself, just thought that you might know that already. gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=3#post-7522 Sat, 07 Jan 2012 17:30:15 +0000 gbulmer 7522@http://forums.leaflabs.com/ siy - I can't remember the exact part number, but we use these LaserStar films: <a href="http://www.megauk.com/artwork_films.php" rel="nofollow">http://www.megauk.com/artwork_films.php</a> It was a couple of years since I talked to the professional PCB folks. I can not remember what was used to strip the tin, sorry. siy on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=3#post-7521 Sat, 07 Jan 2012 14:55:46 +0000 siy 7521@http://forums.leaflabs.com/ I've not yet tried to solder PCBs made with metal resist. As I've mentioned, I've done only few first experiments with it. If my experiments will be successful I'll describe complete process. By the way, those people didn't mention which chemicals are used to strip tin after etching? First experiments show that tin surface looks not very good and I'm not surprised that it might not be suitable for soldering. Also, can you provide more details about 'proper' masking film? gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=3#post-7520 Sat, 07 Jan 2012 14:11:40 +0000 gbulmer 7520@http://forums.leaflabs.com/ siy - I have chatted to people who make PCBs industrially. AFAIK, when they use chemical tin as an etch resist, they later strip that off and re-tin because etching the chemical tin surface (when removing the unwanted copper) also reduces the tins suitability for soldering. Is that what you are finding? gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=3#post-7519 Sat, 07 Jan 2012 14:01:43 +0000 gbulmer 7519@http://forums.leaflabs.com/ siy - Thank you very much for those links and tips. I'll pass on a link to your post to my friend, and we'll see if we can try some experiments. I've never seen the Density Toner before. We have been using 'proper' laser printable masking film, which is translucent rather than transparent, and with the 'hatched polgon' approach has given extremely even dense black. It is about $1/sheet, so we haven't done as many experiments as we might like :-) siy on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7516 Sat, 07 Jan 2012 07:45:15 +0000 siy 7516@http://forums.leaflabs.com/ I see. Polygons is definitely an issue with positive photoresist. I'm experimenting with using chemical tin as resist during etching (this is a step of industrial-like PCB manufacturing process). For this approach photoresist is used only for opening areas of board which should be protected during etching. Then chemical tin is applied and it covers these areas. Finally photoresist is removed and board is etched. One of the advantages of this approach for positive photoresist is that negative mask is necessary (i.e. mask is inverted in comparison to regular use). In other words, with this approach there will be no issues with polygons. So far results are not good enough for actual use, but I just started my experiments and there is a lot of parameters which should be adjusted and then tuned for best performance. As for mask, I'd suggest to use something like this: one <a href="http://www.ebay.com/itm/PCB-UV-Curable-Solder-Mask-Repairing-Paint-Green-100g-/370567399875?pt=LH_DefaultDomain_0&hash=item564789c9c3" rel="nofollow">http://www.ebay.com/itm/PCB-UV-Curable-Solder-Mask-Repairing-Paint-Green-100g-/370567399875?pt=LH_DefaultDomain_0&hash=item564789c9c3</a> It is extremely simple to use in non-industrial environment, although good contrast negative mask is necessary for best performance. If you decide to try it, following things should be keept in mind: 1. The thickness of the solder mask is critical, if it is too thick, it can't be properly polymerized regardless to exposure time; 2. Thin solder mask works just fine and close to industrial two component mask from the point of view of temperature resistance (experiments show that it can handle as much as 400C without any visible consequences) and reliability during soldering; 3. Mask thickness defines the color tint, so uniformity of the solder mask thickness actually defines the look of the PCB; 4. Contrary to description provided with the item mentioned above, it actually requires no chemicals (except washing detergent used to clean the board), no oil based solvent is actually necessary; 5. Actually very small amounts of solder mask are consumed during process, 100g is enough to cover, probably several square meters of PCB surface. 6. Since exposure time if high (usually 30-40 minutes for first exposure, when photo mask is used) requirements to photo mask quality are high; 7. Solder mask is very tolerant to processing times. For first exposure I've tried times from 30mins to 1hour 20minutes with almost equal results. For second exposure at least 40minutes are required, but increasing time at least to 2 hours does not cause harm (I've just not tried longer intervals). Some time ago I wrote a detailed article of the process of applying solder mask with pictures taken during process, but the article is in russian. If you're interested, I may prepare English version of this article with recent changes in process taken into account (the original article describes early version of the process, where oil based solvent was present, later I've found that solvent is redundant). By the way, have you tried to apply toner density spray to printed photo masks? In most cases it is able to convert print of average quality to virtually perfect photo mask. I'm using this one <a href="http://www.kruse.it/html/uk/density_uk.html" rel="nofollow">http://www.kruse.it/html/uk/density_uk.html</a> , but I know that same results were achieved with this one too: <a href="http://www.power-tech.com.au/products/index.php?dispatch=categories.view&category_id=15" rel="nofollow">http://www.power-tech.com.au/products/index.php?dispatch=categories.view&category_id=15</a> gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7508 Fri, 06 Jan 2012 13:45:31 +0000 gbulmer 7508@http://forums.leaflabs.com/ siy - We use presensitised PCB boards, e.g. <a href="http://uk.farnell.com/cif/ab16/pcb-presensitsd-epoxy-2f-100x160/dp/1267741" rel="nofollow">http://uk.farnell.com/cif/ab16/pcb-presensitsd-epoxy-2f-100x160/dp/1267741</a> So there is a positive film mask. We print the film with a laser printer. We believe the black is more even and dense across a hatched polygon area than a solid polygon area. A solid polygon, more than a few mm, is not such an even black when printed as a mask, and seemed pitted by the time the rest of the board was adequately etched. I have access to a etching tank, which uses bubble agitation, and a heater, and the results are very even. We haven't tried making a solder mask. Our boards only get etched and chemically tinned. Our biggest problem is damaging the presentised resist layer when cutting the PCB. siy on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7496 Thu, 05 Jan 2012 17:54:39 +0000 siy 7496@http://forums.leaflabs.com/ Hmm. Do you use dry film photoresist? For dry film photoresist mask is negative and polygons are not an issue at all because printer does not need to print anything at places filled by polygons. For etching, recently I've tried method similar to one seen at this video <a href="http://www.youtube.com/watch?v=Uw0P0Mimbw8" rel="nofollow">http://www.youtube.com/watch?v=Uw0P0Mimbw8</a> (a vibro motor is used to generate waves in the etching solution). Results are very good, in particular in regard to etching uniformity. I'm also adding a border around the main PCB space (just merge Dimension layer to the mask), but for different purpose - it prevents damaging of solder mask during final cutting/milling of board to the required size. gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7495 Thu, 05 Jan 2012 16:48:38 +0000 gbulmer 7495@http://forums.leaflabs.com/ robodude666 <blockquote>Can we try keeping this thread to status updates from LeafLabs people? </blockquote> I think we went off your view of the topic twenty odd posts ago. Maybe LeafLabs should start a proper "status" thread? Or maybe use the blog a bit more? gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7494 Thu, 05 Jan 2012 16:44:15 +0000 gbulmer 7494@http://forums.leaflabs.com/ siy <blockquote>By the way, forgot to mention one important thing related to photoresist technology: the layout should be prepared so spacing between tracks is as uniform as possible and board space without copper should be minimal. ... </blockquote> I try to stick to a rigourous 10/10 track space, and use hatched polygon fills with the same ratio to try to get this effect. The hatched fill seems to work much better than a solid fill, both when printed and when etched. I've been recommended put a 'sacrificial' border of copper around the outside edge. I've tried it, and it seemed to work. This seems to stop fine detail being over-etched. robodude666 on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7493 Thu, 05 Jan 2012 14:17:14 +0000 robodude666 7493@http://forums.leaflabs.com/ Can we try keeping this thread to status updates from LeafLabs people? If you want to discuss new chips, boards, cad stuff, etc. make new threads for them please. -robodude666 gbulmer on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7492 Thu, 05 Jan 2012 14:14:30 +0000 gbulmer 7492@http://forums.leaflabs.com/ LarryP <blockquote>From what Postlathian wrote above, it sounds like STmicro's overview of the F4 is more marketing speak than reality: <a href="http://www.st.com/internet/mcu/subclass/1521.jsp" rel="nofollow">http://www.st.com/internet/mcu/subclass/1521.jsp</a> says: The STM32 F4 series remains pin-to-pin and software compatible with the STM32 F2 series and features more SRAM, peripheral improvements such as full duplex I²S, improved RTC and faster ADCs.</blockquote> I believe the STM32F2 and STM32F4 are very similar. The power circuitry and most peripherals look identical (I haven't looked at every peripherals so there may be some small differences). The current Maple's are based on STM32F1. The functionality at the pins of STM32F1 are comparable to the STM32F2 and STM32F4, but the peripherals implementing the functionality in the STM32F1 are different. I believe Poslathians point is they are different from STM32F1, and hence are quite different from the Maple library. The text you reference doesn't claim anything different. So I think that text you reference is accurate, and compatible with Poslathian, but you seem to be implying that it is misleading. Maybe you were assuming that the STM32F2 was very similar to the STM32F1? (Full disclosure: I am not e member of LeafLabs or ST Micro staff.) LarryP on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7490 Thu, 05 Jan 2012 10:48:49 +0000 LarryP 7490@http://forums.leaflabs.com/ Postlathian wrote: As it turns out, the stm32f2 and f4 chips have radically different peripheral interfaces than the stm32f1, like we use on Maple. So a lot of work has been going into bringing libmaple up to support stm32f4! Greetings all, From what Postlathian wrote above, it sounds like STmicro's overview of the F4 is more marketing speak than reality: <a href="http://www.st.com/internet/mcu/subclass/1521.jsp" rel="nofollow">http://www.st.com/internet/mcu/subclass/1521.jsp</a> says: The STM32 F4 series remains pin-to-pin and software compatible with the STM32 F2 series and features more SRAM, peripheral improvements such as full duplex I²S, improved RTC and faster ADCs. Sigh... Side note: On a forum re NXP's Cortex chips, I posted that IMHO, ARM and their licensees should skip from Cortex M4 to Cortex M6. Anybody who's watched the original Star Trek[*] knows that naming any CPU M5 is just asking for trouble. [*] Star Trek episode, "The Ultimate Computer" <a href="http://en.wikipedia.org/wiki/The_Ultimate_Computer" rel="nofollow">http://en.wikipedia.org/wiki/The_Ultimate_Computer</a> siy on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7475 Fri, 30 Dec 2011 06:22:50 +0000 siy 7475@http://forums.leaflabs.com/ By the way, forgot to mention one important thing related to photoresist technology: the layout should be prepared so spacing between tracks is as uniform as possible and board space without copper should be minimal. Sometimes this requires changes in the track placement in order to allow background polygon fill remaining space. This serves several purposes: simplifies task for the printer, especially at finer resolutions (it prints mostly narrow black lines - most convenient pattern for the laser printers); great improvement in etching uniformity and quality - since etchant needs to remove almost constant amount of copper, time required to do this is also close to constant across the board; finally this extends life of the etching solution, since layout prepared this way usually requires removing of smaller amounts of copper. Probably all of the above is well known approach, but I guess it worth to mention anyway. siy on "State of the Leaf?" http://forums.leaflabs.com/topic.php?id=1204&page=2#post-7444 Mon, 26 Dec 2011 17:28:04 +0000 siy 7444@http://forums.leaflabs.com/ By the way, USB protection/disconnect circuit as it is implemented in my design: <a href="http://we.easyelectronics.ru/uploads/images/00/22/11/2011/12/27/d14b13.png" rel="nofollow">http://we.easyelectronics.ru/uploads/images/00/22/11/2011/12/27/d14b13.png</a>