Oshpark Projects

Thanks both of you for the advices, and welcome back to the forum wight.

@wight
I didn’t know vias may cause problems, i have seen them on pads sometimes and i had assumed that it was ok.
Better to learn it the easy way :bigsmile:
Right, i have overlooked zener mod, i will see what can be done.

@RMM
Can a component be pulled throught those tiny corners? :~
Anyway that can be solved easily, exposed ground ring is 0.75mm width, so i can shrink it to 0.5mm.
Sure, installation and ease of assenbly will be tested in nexts steps.

Thanks RMM. I asume they only have four legs? I have components on order to program the Attiny MCU's hopefully with the help of a very patient member her, I hope. Lets hope its not to late to teach an old Moose new tricks.

No, these ones have 20 pins, but only 8 that are actually used. Start with the regular SOIC-8 MCUs.

I think it just looks that way in the oshpark renders. In their render it enlarges the pads to the point of overlapping, looking like one (or 4) big pads instead of a bunch of tiny ones.

Wow, 20 pins. It will be an achievement for me to do anything with the 8 pin. I'm starting with the 7135 based drivers.

If i understand well how zener mod is done (i am a bit confused with post of different dates, where capacitor is placed before or after diode) i don’t have to tweak anything, zener can be placed just over left side of D1 and C1.

Just a stroke of luck, I designed the board this way, keeping in mind being able to place a C2 for 25/45/85 MCUs.

Aha, I knew something must have changed while I was gone! New tricks!

To better illustrate, here’s a different illustration of RMM’s adapter:

I haven’t used the adapter of course, but I assume that for optimal use solder is lightly wiped across the adapter and allowed to cool. Then one simply presses the MCU against the PCB where it would normally be soldered on. Once you’ve got it in place and held down you can program it normally. Someone may correct me here though. (?)

I am not sure that I understand everything you said. The Zener mod is very simple, but due to my time away I had to think about it / double check a bit. The Zener mod requires two additional components: a low-value resistor (such as 200 ohm) and an appropriate zener (such as MMSZ5229B for example). The resistor should be placed between MCU Vcc and Vbat. The Zener should also be attached to MCU Vcc - it will pull the voltage down to the appropriate level. Without the resistor in place the Zener will burn up. See comfychair’s post #9 here using the userscript I posted in my post #104 here for a semi-illustrated semi-guide to the Zener mod.

Unless I am mistaken, this means that for a Zener build a person would replace D1 with the 200 ohm resistor, then place a Zener between the lefthand pad of the resistor and the lefthand pad of C1. I think that this will be a pain as you have things setup now: trying to set a 0603 or 0805 component on those little diode pads will result in the component wanting to walk/spin… probably getting stuck to C1 sometimes. Stacking the Zener on top will probably also be a bit of a pain.

Everything RMM brings up here is important and worthwhile to think about. I personally also try to keep my component pads out of my GND ring. As you can see by looking at my drivers, I frequently fail. (a) the components can be pulled toward the ground ring (b) the GND ring can get unwanted solder wicked onto it. Mostly (a) is the big problem IMO: sometimes clearances demand that components stay far away from the edge of the flashlight, not skew on their pads towards the outside. Surface tension with solder is surprisingly strong sometimes and will pull a component right off of it’s pads. 7135’s and FETs are notorious for this, which is why I was very careful to implement a small “dam” of resist on drivers like the A17PZL. Without this the 7135’s will pull all the way to the edge of the GND ring. 2-pad passives are not as bad, but it’s still an issue.

You have the main FET current traces taking up all available space. Why not make all traces, even low current ones, on both sides, as wide as there is room for? That would add a little more to the heat transfer, and maybe the capacitance between sides of the board would protect a little against high frequency switching transients.

Thanks wight. I now understand the MCU sits in the middle hence the 20 pins. I was looking at the four on the outside edge.

I measure a diameter of the GND-copper that is always 0.6mm smaller than the board. Got 3 very recent boards here (all ordered last November):
22mm board, 21.4mm copper
17.4mm board (I’m long since overshooting and filing down…), 16.8mm copper.
15.4mm board, 14.8mm copper.

It’s already difficult to solder the boards to some pills. With this added 0.3mm all around it’s nigh impossible.
Thus the workaround.

The 0.8mm PCB is a great option, by the way.
HQ

Thanks HarleyQuin. My measurement of ~0.2mm was for only one edge. I did not measure the overall dimensions of any of the drivers. Still, I think the smallest feeler gauge in my set was 0.25mm and the missing material was less than that much for me. In any case our measurements are pretty similar: ~0.4mm overall and ~0.6mm overall.

Thanks, now is perfectly clear.

That is what i think, but i had found this thread with C1 between resitor and gnd, and i knew that this cap position is something from the past on 1S configurations, but i didn’t know if it still was doing like that for zener mod.

You are completly right, i was so concentrated on finding where to place zener, that i didn’t realize that resistor would have to be soldered on those tiny pads.

That is someting you can take for granted i do, i just was surprised.
I have narrowed exposed GND ring to 0.5mm, i hope it is enough.

I am still working on zener mod capability, but here are the changes I’ve done for the moment:
-Wider traces
-Some components relocated (far from vias)
-Narrower exposed GND ring

Thanks all for the sugestion, if there is someting more you think could be improved, let me know.

https://oshpark.com/projects/BDWjf6DU

Has anyone laid out an 8mm XM-L, MCPCB?

If not, who can?

Thanks!

The problem is that custom MCPCBs (metal core PCBs) are quite expensive. Do you have a source with a decent price?

I wish.

http://smart-prototyping.com/Prototyping-Services/Electronic-Prototyping/LED-Aluminium-PCB-Prototyping.html

Starting price 30$ for 10pcs 5x5cm.

OH!!!

Wonder if gerbers sent to them, the pad under the heat slug could be left open and auto filled with HASL from the factory :wink:

Awesome! Thanks.

I don’t think it’s likely that they will be setup to do that. We also don’t know at what point the fiberglass (dielectric) layer is bonded to the metal core.

No harm in asking though. Worst they can do is say no.

If you make this too narrow and don’t make your PCB larger than 17mm diameter you’ll find that the exposed area of GND ring will sometimes disappear during production. If you look carefully at some other drivers you’ll note that they are setup with a thin exposed GND ring plus larger exposed areas where possible.

The A17PZL is a good example actually. Take a look at the OP in that thread. Note that there are narrow GND rings on the top and the bottom. The primary ring on the bottom is skinnier than the ring on the top. The exposed part of one on the bottom completely disappears when OSH Park produces the board! Fortunately the bottom of that board has exposed scallops which are still there. You can see of of that in the 4 pics in the OP.