{"id":431,"date":"2013-09-29T11:19:41","date_gmt":"2013-09-29T16:19:41","guid":{"rendered":"http:\/\/mikesmods.com\/mm-wp\/?p=431"},"modified":"2013-10-03T21:30:16","modified_gmt":"2013-10-04T02:30:16","slug":"hacking-the-macbook-pro-retina-lcd-part-4-first-pcb-tests","status":"publish","type":"post","link":"http:\/\/mikesmods.com\/mm-wp\/?p=431","title":{"rendered":"Hacking the Macbook Pro Retina LCD, Part 4: First PCB Tests"},"content":{"rendered":"

Welcome back!\u00a0 It’s been more than a month and a half since my last post on the Macbook Pro Retina panel – damn my “real job” and the time it consumes.\u00a0 But we’re here now, so let’s dive into things.<\/p>\n

In the previous two posts on this subject, I have talked about two boards that I have been developing for the 15.4″ Macbook Pro Retina display assembly: a breakout for the FaceTime camera, and the main display controller \/ backlight driver board.\u00a0 Well, in the month-and-a-half that has elapsed, both boards have been received and built.\u00a0 Let’s start by taking a look at the former.<\/p>\n

Camera Breakout<\/h4>\n

When I went to order these boards, I did so immediately after the cutoff for the current OSH Park 4 layer order, so the estimated delivery time was three or four weeks.\u00a0 Unhappy and impatient, I held off and instead ordered the board as 2-layer for more instant gratification.\u00a0 The two inner layers are only GND, so this is possible without too much trouble.\u00a0 It throws off the impedance of the USB traces probably significantly, but as the entire trace length is a half inch or so, I figured it’d be close enough for at least temporary use.<\/p>\n

So the boards arrived a week and a half later.\u00a0 I immediately noticed something interesting and bothersome.\u00a0 Board fab houses typically require a gap between the edge of any copper and the routed board edge.\u00a0 If you are making a small board and including mounting pads for screws, the pads may consume a large percentage of the total board area – in fact, the pads may well drive the overall dimensions of the board, and larger dimensions mean greater board cost.\u00a0 I wanted this board to screw mount, but even the 2-56 screws I designed for needed quite significant pads.\u00a0 I decided it would be nice to trim the amount of room wasted on mount pads by clipping the pads at the board edge, allowing the screw to extend into the no-copper area at the edges of the board – it really only drops a few cents from the board in this case, but it makes me feel better.<\/p>\n

So in Altium Designer, I made a small Pad on Multilayer (the magic layer which is copied to all other layers), then made a Polygon in the shape of a circle with a flat edge and also placed this on Multilayer.\u00a0 In theory, this should have resulted in a round pad with a flat edge, drilled and plated through as expected – in fact, the 3D render of the board shows this:<\/p>\n

\"For<\/a>

Mount pads look OK here.<\/p><\/div>\n

But what arrived from the fab was this:<\/p>\n

\"There<\/a>

There aren’t supposed to be voids in those mount pads…<\/p><\/div>\n

When I poured the rest of the GND polygon, apparently Altium attempted to connect to the inner Pad, and generated Polygon Cutouts surrounding it, which happened also to cut the Multilayer polygon.\u00a0 It didn’t show in the PCB editor, although it did in the Gerbers – but I was in too much of a hurry when ordering to notice.\u00a0 Oops.\u00a0 But so be it, it’s only the mount pads.<\/p>\n

I then assembled the board, and with bated breath, plugged it into a USB port.\u00a0 And Hooray!\u00a0 The Device Connected sound sounded, and the camera showed up in device manager.\u00a0 But, strangely, the power LED was orange.\u00a0 I specified a green LED, I thought I placed a green LED, but it was bright orange.\u00a0 I checked the package to be sure but it was correct.\u00a0 It was then that I discovered a tiny short, and simultaneously learned that if you apply 5V directly across a 2.1V green LED, it becomes an orange LED.\u00a0 Neato!\u00a0 It also gets real real hot.\u00a0 But miraculously, after I corrected the short, which had caused the full USB voltage to appear across the LED, it returned to green and operated as normal.\u00a0 So I guess I can say, these OSRAM CHIPLED parts seem to be pretty hardy!\u00a0 I unfortunately don’t have any photos, but these parts are cheap, so buy some and experiment for yourself.\u00a0 Science!<\/p>\n

After a few days the 4 layer board order deadline had arrived again, so (having not discovered nor corrected the pad issue) I re-ordered the board as 4-layer, this time adding a second transient suppressor for the ALS connector… because why not, and you can always short it with jumper wires if you don’t want to use it.\u00a0 So here’s what that looks like (note that I have fixed the pad issue at this point):<\/p>\n

\"Yep.\"<\/a>

Yep.<\/p><\/div>\n

I haven’t bothered to build this one yet, but it hasn’t changed significantly since the 2-layer version, so I suspect it’ll work fine.\u00a0 The files for this board can be downloaded here:<\/p>\n