[Gta04-owner] GTA04A5/Letux 2804: status update

H. Nikolaus Schaller hns at goldelico.com
Fri Mar 4 10:23:02 CET 2016

Hi Martin,

Am 03.03.2016 um 21:43 schrieb Martin Rottensteiner <martin.rottensteiner at gmail.com>:

> Hello list, hello Nikolaus,
> sorry for german language, i chose the wrong recipient.
> I know a guy who worked many years in repairing small electronic parts for a large company (i forgot its name). He now runs a repair shop for cell phones in my town. I asked him if he knows how to change such a very small chip. He said that this is no problem. He asked for a photo of the chip and he said he could then tell me how to change it. 
> Maybe it would also be an option for you to ask around in cell phone repair shops in your town?

Many thanks for your suggestions!

The problem is less that we don't know how to do it but to do it with the tools and machines we have.

Usually rework is done with a machine like this:


It costs ca. 20-30000€. 

But this method does not guarantee that a rework is successful for a single given unit because PCBs and components are stressed during the rework process. A cell phone repair shop usually has 100 broken devices and wants to make 80 working out of them. So if any isn't working after rework they can take the next one.

Or if the customer comes with a device they don't know (like a GTA04) they probably decline to do anything for it unless it is a simple task (adding a new USB connector for example or replacing battery or display).

What we have is this machine (was also expensive) which is less stressful during the soldering process:


This type of soldering machines is perfect for mounting stacked packages like OMAP+PoP RAM on a fresh PCB. What we are missing is a tool to precisely and reliably solder a new OMAP+PoP RAM to an existing board (where the old OMAP has already been removed).

Anyways, our new helping tool should arrive today and we will see if it better fits.


>     Yours, Martin
> On Thu, Mar 3, 2016 at 6:40 PM, Martin Rottensteiner <martin.rottensteiner at gmail.com> wrote:
> Hallo Nikolaus,
> Ich kenne einen Handyreparateur in Graz, der viel Erfahrung mit Reparatur hat. Er hat mir gesagt, wenn du ein Foto schicken würdest, würde er sagen können, wie der Chip zu tauschen ist.
>      LG Martin
> Am 25.02.2016 14:22 schrieb "H. Nikolaus Schaller" <hns at goldelico.com>:
> Hi all,
> Am 19.02.2016 um 18:50 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> > Hi all,
> > I have promised to give more regular status updates on this project.
> >
> > 1. WLAN 5 GHz
> > from the discussion I got the impression that there is a majority who
> > wants 5 GHz. It is just replacing the WL1835MOD with WL1837MOD
> > and one chip antenna with a different one.
> >
> > So we can decide between at the last possible moment, which is when
> > components are ordered.
> >
> > There is also some discussion about new FCC rules. Well, we already have
> > the problem that we don't have source code for the firmware of the module.
> >
> > Rather, we have to download a firmware blob from Texas Instruments to
> > use the module. And I assume that the boot loader of the module does
> > some CRC check, so nobody (and we as well) are able to modify the firmware
> > that is certified. Since the modules already have a FCC precertification,
> > this is sufficient to fulfill all new rules that nobody can modify the radio
> > spectrum.
> >
> > It is not nice because it is against our idea of software/firmware freedom,
> > but to be honest, we are a too small project to change the world. We can
> > only fight where we can, and that is the application processor running
> > free and open software (Debian, Replicant, QtMoko etc.).
> >
> > 2. Time plan
> > I had planned to make the 1GB RAM soldering experiments this week,
> > but the tool to help getting a tiny amount of solder paste on the chips did
> > not yet arrive. Looks as if it comes mid of next week.
> The tool we have designed was manufactured and did arrive in time. But it
> does not yet work as expected. So we will have to get a modified variant.
> Some of you may be interested in what we are doing here, so let me explain
> a little:
> The key task is to rework an existing GTA04A3 or A4 board with the 1 GByte
> RAM chip before we can have all GTA04A5 produced with that one.
> The good thing is that we can take a fully populated GTA04A3/A4 board and
> already can remove the OMAP and the PoP chips. This is a process which
> works fine without damages.
> The other way round is the difficult one: to solder a new chip onto an existing
> PCB where there is already some solder on the copper pads. Initial experiments
> were disappointing. The chip did swim on the solder flux and was soldered
> after moving several 100µm to the side.
> On a fresh PCB we use a laser cut stencil which allows to print a very tiny
> amount of solder paste on each of the contact points of the OMAP3 BGA.
> This solder paste "glues" the chip at the right position and there is not too
> much flux and therefore the chip does not swim away during reflow soldering.
> But since we already have components on the boards for rework, it is
> impossible to use the stencil printer and print solder paste onto the PCB.
> So the idea is to print the solder paste on the OMAP chip (it is like if you
> want to glue two things together: it usually doesn't matter on which part
> you put the glue on).
> This is where our specially designed tool comes into the game. It should
> allow us to to place the OMAP CPU chip (which is just 12 mm  x 12 mm)
> in the stencil printer and keep it in place.
> Basically it works, but what does not yet work is to fine-adjust the stencil
> so that the tiny openings (ca. 300µm diameter) are exactly over the OMAP
> BGA balls. So we get the solder paste printed at the wrong locations.
> You may wonder how others are doing such rework. The answer is: they
> rarely can do it with such fine-pich and package-on-package chips (like the
> OMAP3 is) at all. It is a task that many SMD repair houses decline to do.
> And unless you have miniaturized systems like smartphones, chips are
> much bigger, less critical in placement, reballing and resoldering.
> There are even DIY videos on youtube. But that is for 1mm pitch (and not 0.4mm).
> Or they have a very expensive rework station with laser optics, vacuum nozzles
> and 4D positioning system. And everything in precision for 100µm.
> This is where we hope the redesigned tool will be better. Next week.
> BR,
> Nikolaus
> >
> > 3. Letux Kernel
> > is getting more stable again as we test it now on the Pyra hardware and
> > the GTA04. This reveals some tiny subtle bugs. Nothing really important,
> > but for the future (e.g. an issue in the touch screen driver).
> >
> > BR,
> > Nikolaus
> >
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