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Sometimes all it takes to build something interesting is to put the same old parts together in different ways.[Sayantan Pal] did this for the humble RGB LED matrix, creating an ultra-thin version by embedding the WS2812b NeoPixel LED in the PCB.
The popular WS2812B has a height of 1.6 mm, which happens to be the most commonly used PCB thickness.Using EasyEDA, [Sayantan] designed an 8×8 matrix with a modified WS2812B package.A slightly smaller cutout was added to create a friction fit for the LED, and the pads were moved to the back of the panel outside the cutout and their assignments were flipped.The PCB is assembled face down, and all pads are soldered by hand.Unfortunately, this creates a fairly large solder bridge, which slightly increases the overall thickness of the panel, and may not be suitable for production using traditional pick and place assembly.
We have already seen some similar approaches to PCB components using layered PCBs.Manufacturers have even begun to embed components in multilayer PCBs.
This should be the new standard for packaging things!Using a cheap four-layer board, we do not need so much wiring area, and can easily be socketed or manually soldered to replace DIP.You can surface mount the inductor directly on the top of the chip in the PCB of all its passive components.Friction may provide some mechanical support.
The cutting can be slightly inclined or funnel-shaped and done by a laser cutter, so wedging the part does not require much precision and can be reworked by heating and pushing out from the other side.
For a board like the photo in the article, I don’t think it needs to exceed 2L.If you can get LEDs in a “gull-wing” package, you can easily get a flat and thin component.
I wonder if it is possible to use the inner layer to prevent soldering on the outer layer (by making a small cut to access these layers, so the solder will be more flush.
Or use solder paste and oven.Use 2 mm FR4, make the pocket 1.6 mm deep, place the pad on the inner bottom, apply solder paste and stick it in the oven.Bob is your father’s brother, and the LEDs are flush.
Before reading the entire article, I think better heat transfer will be the focus of this hacker.Skip the copper of the n-layer board, just put any type of heat sink on the back, with some thermal pads (don’t know the correct terminology).
You can reflow the LED to a polyimide (Kapton) film type printed circuit instead of hand-soldering all these connections on the back side: only 10 mils thick, which may be thinner than hand-soldered bumps.
Doesn’t the common structure of these panels use flexible substrates?Mine is like this.Two layers, so there is some heat dissipation-which is very much needed for these larger arrays.I have a 16×16, it can absorb a lot of current.
I would rather see someone design an aluminum core PCB-an amide board adhesive layer glued to a piece of aluminum.
Linear (1-D) strips are commonly found on flexible substrates.I have not seen a two-dimensional panel with this structure.Is there a link to the one you mentioned?
A thin aluminum core PCB is useful as a heat sink, but it still gets hot: you still need to dissipate the heat somewhere in the end.For my higher power array, I laminated a flexible polyimide (not amide!) substrate directly onto a large finned heat sink with thermal epoxy.I do not use pressure sensitive adhesive types.Even if there is only convection, it is easy to dump >1W/cm^2.I will run at 4W/cm^2 for a few minutes at a time, but even with 3 cm deep fins, it will become very delicious.
Nowadays, PCBs laminated on copper or aluminum boards are very common.For things I use myself, I would recommend copper-easier to bond than aluminum.
Unless you solder the device to copper (by the way, if appropriate), I find that hot epoxy bonding to aluminum is much better than copper.I first etched aluminum with 1N NaOH solution for about 30 seconds, then rinsed with deionized water and dried thoroughly.Before the oxide re-grows, it is bonded within a few minutes.Damn near indestructible bond.
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