[Success!!!]: X31 ULV mod with Dothan CPU

[Raceboy]

I received a dead X31 which is otherwise in very nice condition (top lid is new, battery has few cycles and holds good charge) but after teardown, it appeared to had a liquid spill as the cause of death.

I purchased a replacement mobo from the kind board member (with the same 1.4GHz CPU) which is on the way but looking at the board made me wonder. It has regular (non LV) Banias CPU and since I have also a dead X41 board with Pentium M 778 (1.6 GHz LV chip) I thought about swapping it onto X31 board. The chips are electrically 100% compatible and the BIOS supports Dothans too (same bios for both X31 and X32), so why not.

Obviously I won't do it on the arriving working board first but rather try to revive the board after spill (it's easier when you have working board for measurements). I already removed the 778 from the X41 board (no probs) and I will try to solder it onto X31 board.
Since X32 also did not receive LV chips, only regular Dothans, it is worth it IMO. Max TDP on the 1.4 GHz Banias is 22W but on 778 it is only 10W! That is more than twice less!

Of course, if anyone feels like contributing to this quest by throwing a working (can have passwords, whatever, just has to boot to bios) X31 board to mail, it would help a lot

I kinda like the idea of having ultra-portable that has enough punch but at the same time has great battery life also. My TR451 which has "ULV" Dothan (740 that runs @ 400 MHz FSB and is heavily undervolted), 16GB CF card as a HDD gets around 8 hours on a 9cell which is 12% worn. And that is with wireless enabled and brightness on 2/3. That is something!

[sjthinkpader]

Most of the ULV versions were shipped in Asia. Quite a bit to Japan. I saw a used board came up in Malaysia but it was pretty expensive.

[Raceboy]

Ahh, I confused you!

I don't mean to track down native ULV X41 board but go for LV (778) which I already have in my hands and undervolt it like I did on X41 which would effectively become ULV then.

For thos who are interested, BGA 479 stencils are available on ebay for $5.89 (free shipping) and 0.76 mm solder balls that BGA Dothan uses are only $3.89 for 25k pcs (free shipping also).

[sjthinkpader]

Ok, once you put down the solder paste using this stencil, you plan to put down the solder balls one by one?

[Brian10161]

I'm interested to see how your progress on such a project will be. It looks very interesting.

I would never do this for too much fear of wrecking the laptop. Subscribing to this topic to see how goes!

Good luck mate!

[sjthinkpader]

I saw an automatic machine putting down solder balls on bottom of a BGA. Whenever someone say they will do this as a home project, I get a chuckle.

[Raceboy]

You don't put them one by one. You apply BGA flux on the chip, put the stencil on the chip, pour the balls onto it, make sure all holes are filled and then wipe other balls off with a brush. Then heat the balls a bit so they stick to the chip, then put the chip onto its pad on the system board and then heat it with the solder station.

It'a easier than it seems and once you've done it couple of times, it's easy. It's only hard for the first times you do it because lack of experience.

I have to source another board because the one I bought did not have a subcard that contains a security chip. Since I cannot use the one from my 2nd board (as I use it in my X31), I have to wait until I have sourced another board.

If anyone has an X31 board laying around, please contact me. I would buy it. It can be with passwords etc, that don't matter but the subcard has to be present.

[Raceboy]

So, after the stencil for BGA479 (~$7 from ebay) and 0.76mm solder balls (~$5 from ebay for 25k pcs) arrived and I found some time, I went for it. And I decided to do it manually, without soldering station and used my old trusty heat gun with precisely adjustable temperature range (I have reflow the GPU's numerous times before with it successfully)
I ordered a special BGA gel flux (€11 from local electronic shop) also, I would never recommend doing with anything else as usual soldering paste starts to boil and messes up the balls.

As I had the stencil but no place to attach it and the chip, this is the most time-consuming thing: to align it and to have all the balls there. Took some tries on the first time and for my friends X31 it took only about 5 minutes

Here are the balls in place: http://www.porsche-foorum.org/album/alb ... l_CPU1.jpg

After balls are there, heat the chip until all the balls are in liquid state and remove the stencil with steady hand.

I cleaned the pads on the motherboard well from old soldering with isoprophyl alcohol and heated it with heatgun after wards so the pads would melt and become equal.
After that applied BGA flux, put the chip in place and applied heat. Note that I only do it from underside (pre-heat to 100C and then 350C). You know when it is ready by touching other components in each corner with the screw-driver. If the are loose, then lower the temperature to 100C and after ~1 minute let it cool down at least 10 minutes.

Here's how it looked after install: http://www.porsche-foorum.org/album/alb ... l_CPU2.jpg

I went for Pentium M 758 (1.5 GHz/2M/400) because this chip overclocks easily to 2 GHz (533 MHz FSB) and I am planning to do this later (same mod applies like on T40-T42 by putting a jumper on the clock generator). The other wires from the chip in the upper part of the photo are my COM port mod (Rx, Tx and GND), I used 2.5mm audio jack on the back panel).

And suprise, it POST'ed nicely: http://www.porsche-foorum.org/album/alb ... l_CPU3.jpg

Haven't had time to test it too throughly but will do it after my trip to Africa next week.

But, Im happy and now I have pretty much ultimate X32s as I like to call it: IPS panel (XGA), Dothan LV (with possibility to overclock to 2 GHz with a switch on the side), SSD and brand new genuine Panasonic battery. I love it!

[dr_st]

Wow, talk about technical skills!

Your machine is indeed amazing. I have a partiality to X3x series. My X32 is somewhat similar to yours, except it's a standard voltage Dothan, so no over/underclocking with a switch (although I can probably underclock/undervolt it using NHC).

[Raceboy]

Thanks!

The switch is exactly for usage on purely needed basis because mostly use the laptop for tuning engine management systems on cars and I need maximum battery life. This is one of the biggest reasons I did this mod: TDP of the original 1.4 GHz banias chip is 22W but on the Pentium M 758 it is 7.5W! Graned it is maximum but the Banias couldn't handle 0.700 volts @ 600 MHz (it was stable at 0.732 volts), but 758 has no problems with this.

Did I mention that the fan never runs except when switching on the laptop? It doesn't run even on high loads (CPU stays below 50C at full load with the X31 heatsink which is huge compared to X41 one).

[poshgeordie]

@ Raceboy: I'm totally impressed with what you've done - we commercially reball chips, and you've done a great job.

One thing will help you (psst - don't tell anyone else this!!); use the flux paste on the chip and use a flat edge (eg a credit card) to scrape it off again - it leaves a very thin surface of flux. Then put the template on the chip and put all the solder balls on the chip.
Because you have the flux already on the chip, you can carefully lift the template off the chip and you'll need much less heat to melt the balls onto the chips.

Once again - I am very impressed indeed and I don't say that too often!

[Raceboy]

Thanks for the tip and kudos, Nick. I guess I did pretty much the same way though? I applied the flux on the chip and then the stencil, that way the balls stick better when you brush the excess off. But removing the stencil before heating the balls did not work for me, at least it was easier to heat the balls up, that way it worked 1st time I tried.

Reballing the CPU is sort of easy because it has big balls (no pun intended) and a decent pitch compared to GPU, which has only 0.6mm balls.