Upgrading RAM in the average computer is a relatively trivial task. Pop the case open, and you slide the new sticks into the extra slots. It’s not the same case for smartphones and tablets — in the endless quest for the slimmest form factor, all parts are permanently soldered. In addition, every device is essentially bespoke hardware; there’s no single overarching hardware standard for RAM in portable devices. You could find yourself searching high and low for the right chips, and if you do track them down, the minimum order quantity may very well be in the thousands.
Unless, of course, you had access to the Shenzhen markets where it’s possible to buy sample quantities of almost anything. Given access to the right parts, and the ability to solder BGA packages, it’s a simple enough job to swap a bigger RAM chip on top of the CPU during the repair.
It was but two weeks ago when I told my story of woe — the tale of an LG Nexus 5X that fell ill, seemingly due to a manufacturing fault at birth. I managed to disassemble it and made my way through a semi-successful attempt at repair, relying on a freezer and hairdryer to coax it back to life long enough to backup my data. Try as I might, however, I simply couldn’t get the phone running for more than ten minutes at a time.
All was not in vain, however! I was rewarded for documenting my struggles with the vast experience and knowledge of the wider Internet: “Hairdryers don’t get as hot as heatguns!”
It turned out I had just assumed that two similar devices, both relying on a hot bit of metal and a fan as their primary components, must be virtually identical if rated at a similar power draw. I was wrong! Apparently the average hairdryer stays well cooler than 150 degrees Celsius to avoid melting one’s silky locks or burning the skin. I even learned that apparently, wet hair melts at a lower temperature than dry hair. Who knew?
Armed with this knowledge, I rushed out and bought the cheapest heat gun I could find — around $50. Rated up to 600 degrees C, this was definitely going to be hotter than the hairdryer. With the prevailing opinion being that I had not applied enough heat in general, I decided to also increase the heating period to 90 seconds, up from a quick 30 second pass originally.
Warranty shmarranty — toss the phone in the oven! There’s apparently a problem with the assembly of the Nexus 5X smartphones, and it looks like it is due to faulty BGA chip soldering. LG USA has had enough problems with the phone that they may not even have enough parts or new units to fix it, so they’re offering a refund. But we all know how it is to get attached to a device, right?
So [Alex] disassembled his beloved phone, pulled out the board in question, and gave it the XBox Red Ring Of Death treatment. He placed the board on some insulating aluminum foil, and baked it for six and a half minutes. Season with lemon and pepper, and serve! We’re honestly surprised that sticking the affected board into the oven at 195° C / 390° F for a few minutes would work at all. Isn’t that a low temperature for soldering, especially with a lead-free mix? Could it have been a problem with humidity after all? Continue reading “Nexus 5X Phone Resurrected By The Oven”→
It’s well-known that buying Flash storage devices from cheap online retailers is fraught with danger. Stories abound of multi-gigabyte drives that turn out to be multi-megabyte ones engineered to falsely report their capacity. So when [Jason Gin] found a source of 64GB Toshiba eMMC chips for only $6 per device he bought a few, but was prepared for disappointment.
To test them, he decided to use an SD card interface. There are minor differences between eMMC and SD, but the interfaces are electrically the same and in most cases an SD controller will happily do business with an eMMC. It was not however an easy task to connect the two — these eMMCs were in BGA packages, hardly the easiest ones to work with. He resorted to dead-bug soldering the relevant interface wires to SD lines, and connecting up his computer.
His first attempt was something of a failure, wiring the chip to the PCB of a cheap USB-to-SD adaptor. This did not put him off though, he followed it up by cracking open a very old 2GB SD card that contained a PCB instead of being potted, and soldering his eMMC in place of its Flash and controller. This even fit in the original SD housing, and met with success when plugged into more reliable SD card readers. He was thus able to confirm the capacity of his chips.
His blog post is worth a read for more than just the very fine soldering involved. He takes us through some of the intricacies of SD interfacing, as well as talking at length about the decoupling and termination required to make a reliable connection. We particularly like his use of an area of unconnected BGA balls as prototyping space for decouplers.
One day [Andy] was cruising around eBay and spotted something interesting. Forty Virtex-E FPGAs for two quid each. These are the big boys of the FPGA world, with 512 user IO pins, almost 200,000 logic gates, packed into a 676-ball BGA package. These are not chips designed for the hobbyist. These chips are not designed for boards with less than six layers. These chips aren’t even designed for boards with 6/6mil tolerances from the usual suspects in China. By any account, a 676-ball package is not like a big keep out sign for hobbyists. You don’t turn down a £2 class in advanced PCB design, though, leading to one of the most impressive ‘I just bought some crap on eBay’ projects we’ve seen.
The project [Andy] had in mind for these chips was a generic dev board, which meant breaking out the IO pins and connecting some SRAM, SDRAM, and Flash memory. The first issue with this project is escape routing all the balls. Xilinx published a handy application note that recommends specific design parameters for the traces of copper under the chip. Unfortunately, this was a six-layer board, and the design rules in the application note were for 5/5mil traces. [Andy]’s board house can’t do six-layer boards, and their design rules are for 6/6mil traces. To solve this problem, [Andy] just didn’t route the inner balls, and hoped the 5mil traces would work out.
With 676 tiny little pads on a PCB, the clocks routed, power supply implemented, too many decoupling caps on the back, differential pairs, static RAM, a few LEDs placed just for fun, [Andy] had to solder this thing up. Since the FPGA was oddly one of the less expensive items on the BOM, he soldered that first, just to see if it would work. It did, which meant it was time to place the RAM, Flash, and dozens of decoupling caps. Everything went relatively smoothly – the only problem was the tiny 0402 decoupling caps on the back of the board. This was, by far, the hardest part of the board to solder. [Andy] only managed to get most of the decoupling caps on with a hot air gun. That was good enough to bring the board up, but he’ll have to figure some other way of soldering those caps for the other 30 or so boards.
Modern surface mount components often need special tools for rework. However, those tools can be expensive. [Michael Skrepsky] wanted an infrared rework station, but didn’t like the price. So he built his own.
According to [Michael] he used a lot of scrap in the construction. . He used K-type thermocouples, optotriacs, triacs, a 20×4 display and, of course, an Arduino. An old bathroom heater, along with a 600W and 100W halogen bulb work as heaters.