Rigol DS1052E nasty surprise!

[hisense999]

It is interesting that, though the AD8370 and the LMH6552 within the analog front-end shielding retain their diacritics grinding-out, this is not the case for the ADC chips anymore! The five ADCs proudly present their identity now, being devices manufactured from AD and waving their obscure identity in three lines:

Code: [Select]

RAD0182A
#1032
1924219.1
Of course, I guess that if I purchased those quantities of the AD9288 ADC chip Rigol does from AD, the latter ones would be happy to put a picture of my face onto the chip instead of the traditional boring identification marks!

Actually AD will not change even one digit on the chip maybe if you are really super customer and ordering separate version in hundred of thousands qtty, this which use RIGOL is a common service in China which cost about 1 Yuan for scratch and repaint MCU, is a big fun usually we scratch all our MCU's to not give a fun for ppl which open device, sometimes after scratching all digits we order painting in PIC or AVR style this is a big fun I wonder how many ppl try to extract this as simple PIC or AVR

[hisense999]

I didn't know that manufacturers would end with such low-tech tricks to hide their secrets

I know however that it is a pretty common practice to "decap" chips to read the actual die marking or even to decipher the Flash content bit by bit... See this hacking of a PIC 18F1320 and also this site for details.

So this kind of "protection" would only be good against naive hobbyists like us, not against real competitors. Which may be the actual purpose, anyway!

Or maybe that's just a requirement from the chip manufacturer in order to hide the ADC overclocking capabilities?

Yes this is low-tech trick but working quiet good, you look at this from advanced point of view, yes decap process is simple but first you must know where to decap second, you must contact negotiate price, make an transfer send an IC then wait for result everything need a time and if you have a lucky then person involved in copy idea start to be bored cuz nothing simple looking at start and instead of reverse engeenering this device he can pick up other more simple or even forget at second day about it.

B.R.

[marmad]

So this kind of "protection" would only be good against naive hobbyists like us, not against real competitors. Which may be the actual purpose, anyway!

I think all protection schemes are mostly aimed at competitors - not so much at hobbyists.  It seems that, in any field of electronics where competition is high, and innovation and/or price is critical to success, anything companies can do to make it more difficult to copy their designs (specially if it doesn't cost much money) often will be done.

I remember back in 1979 my Arp Odyssey analog synthesizer had it's filters completely dipped and encased in a block of colored epoxy to make it impossible for competitor Moog to identify any of the components.  And that area on the schematic - which they still delivered with products back then - just showed a block with inputs and outputs.

[rf-loop]

Maybe originally they want make copycats work more delay? I understand if there is some technical innovation in design but there is nothing if think electronics, but maybe this "big innovation" is "how it can make cheapest way keeping it still acceptable in its price class". Digital oscilloscope designed so that ADC and front end is most weak point (but still it is acceptable if think price).   Maybe they also want hide  that they use cheapest -40 models but use these as -100 specified. They use 100MHz clock for chips what are specified for 40MHz by Analog Devices. How to make oscilloscope with ~100USD, this info need try keep littlebit scrambled. Maybe this was most high level innovation as they start with this design. After then Atten make copy. In court Rigol win but still Atten/Siglent look this just as "so what".

Quality is one thing what can not copy so easy together with lower price.  Quality is very good product protection. After chinese really understand it.... they win. Quality in design can not copy only if look schematics. (in history HP understand it and all schematics was included with manuals, becouse they know... no one can copy it so that it still can be good business to copy cat.  Today situation is littlebit different with low-end products. Everyone can do these. Question is only - who can make it more cheap and so that it is still some business. (business need also name... no one buy expensive high-end product with "noname" if there is same time with nearly same price and quality class Agilent on Tektronix)


All these ADC's are made as 100MHz chips! But not all chips reach full speed and accuracy in analog sampling and conversion. It is not overclocking digital logick parts but with 100MHz adc accuracy is poor. Digital part works normally this full speed.

[A Hellene]

Hello there!

I am sorry for my short absence, my fellow EEVbloggers.
These days I am playing the good host, since I have guests at home --and my day has only 24 hours...
But I am not complaining.


tinhead,

I reassembled my unit to take some live readings: When the 20MHz BW limit option is disabled the 595.QA (that drives varicap's anode) is logic high (+5V0) and the buffered DAC output (that drives varicap's cathode) is -5V02 at the op-amp output (before the 100 ohm resistor at TP107/TP108), thus the varicap reverse bias becomes 10V0 and its capacitance becomes 1.8 .. 2.5 pF (the datasheets claim 2.7pF @ Vr=4V7). With the BW limit enabled, 595.QA is logic low (0V0) and the buffered DAC output is +3V78, so the varicap is forward biased and in full conduction, shunting the two 150p bandwidth limiting capacitors (Quick calculation: (150pf/2)//95ohm gives -3dB at 22.3MHz).

Regarding the ADCs, I believe that your estimations are spot on. By the way, only the trigger output digital lines are not sandwiched within the inner layers, since they can be seen on the bottom layer, properly terminated; the front-end signal outputs are not visible at all...

In Rigol, all the five "A" ADC differential inputs (the AD9288 pins 02 and 03) are in parallel as well as the remaining five "B" ones (the AD9288 pins 11 and 10), forming two 8-bit 500MSa/s ADC logic units (let's call them unit A and unit B) with the five physical ADCs being clocked in sequence (interleaved) by the FPGA PLL. The AD9288 S-configuration input is hardwired to logic high (S2:S1 = 0b11), so we have 180 degrees data alignment between the units A & B, making it possible to create one 8-bit 1GSa/s ADC logic unit by feeding the two partial 500MSa/s logic units with the same analog signal and clock input without the need of reconfiguring their clocking scheme.

This is the truth table of the ADC feeding relays (in my schematics: the Relay#1C that feeds the ADC logic unit A input, and Relay#2C that feeds the ADC logic unit B input):

Code: [Select]

-----------------------------------
 |1GSa/s  Ch1   Ch2  | Rl#1C Rl#2C |
 |---------------------------------|
 |  Off   Off   Off  |   1     0   |
 |  Off   Off   On   |   1     0   |
 |  Off   On    Off  |   1     0   |
 |  Off   On    On   |   1     0   |
 | - - - - - - - - - - - - - - - - |
 |  On    Off   Off  |   1     0   |
 |  On    On    Off  |   1     1   |
 |  On    Off   On   |   0     0   |
 -----------------------------------For example, when both the relays are off, the system is configured to sample Ch2 at 1GSa/s.
______



hisense999,

Isn't it obvious that I was joking about putting my face on the markings?
On the other hand, in volume customers (with purchases in the order of 10,000's or 100,000's or more units), I know that the manufacturers can agree even to pre-load some firmware and/or change the IC diacritics.

But, like Squonk, my question is, why obfuscate the ADCs only and keep grinding out the other two front-end chips (the VGA ans the diff-amp)?
______



marmad,

I agree with you. A decent EE will finally find everything out; these practices can only delay them.
After all, a real EE will mostly choose to redesign something rather than take the time to completely reverse it.
______



rf-loop,

You are absolutely right about that nasty detail, called quality: It cannot be copied and it is the worst enemy of all the cheap copycats!
______



Anyway, I have drawn the schematics of the analog section and I will publish them shortly, right after I make them a little more readable than what they currently are. Right now I am trying to trace down a couple or three blind signal lines that terminate unexpectedly, since they go to a via and disappear into the four PCB inner layers, making it unable to find their destination.

Since I have not yet found anything odd in the design, according to the schematics I have drawn, I guess that what remains to do is to reflow the BGA package FPGA. After all, the malfunction of my device points to the direction of a possible bad solder joint; and the BGAs that run hot are notorious for this kind of failures --especially after the Pb-free directives enforcement era of producing junk devices that will die with mathematical accuracy the next day after their warranty period expires...


-George



[EDIT 1]: Uploaded the Ch1 analog front-end schematic sheet*.
[EDIT 2]: Uploaded the Trigger Input front-end schematic sheet*.
[EDIT 3]: Uploaded the DAC/Demux/Sample & Hold/Buffers schematic sheet*.
[EDIT 4]: Uploaded the Trigger/Comparator schematic sheet.
[EDIT 5]: Uploaded the Keypad & Indicators PCB schematic sheet.
[EDIT 6]: Linked to the DS1000E/D PSU schematic sheet, in the first page. I am sorry for that omission...


(*) Credits go to Squonk for spotting and reporting to me two(!) of my copy-and-paste errors in the previously uploaded Ch1 front-end schematic, an omission in the Trigger Input front-end, and a clarification in the DAC/S&H sheet! So, please, get the updated, correct ones.
Thank you, once more, Squonk!

[A Hellene]

Squonk, thank you once more for pointing out the errors and omissions in my schematics!
Creating schematic sheets is an art; but my copy&paste skills seems to be getting worse, especially when my time is limited...

Anyway, I corrected the diode omission in the trigger front-end sheet and made a clarification in the S&H one, where it is now clear that the S&H capacitors are not next to the demultiplexing chips; actually, they are located next to the buffer inputs to avoid the long line noise or any oscillations.
Please, download them again.

More on your comments in a following message.


-George

[A Hellene]

Ah, that's easy --and it gets even easier if you have to create from scratch the components your CAD software does not already include within its installed libraries!

It is obvious, though, that these schematics are drafts: They are even drawn not in graph-paper (for better alignment purposes) but in blank printer-paper sheets (that are not eraser-friendly) I have in abundance!


-George

[A Hellene]

Re-edited the message above, to add another sheet of the Trigger/Comparator schematics.


-George

[saturation]

Same here, Hellene is the wizard worth watching

I still like pencil schematics, fast and easier ... schematic tools are nice for presentations and PCB outsource work, but less for works in progress and hacking!

Wonderful!

I am following each schematic release with much more interest than in Harry Potter's next episode

[tinhead]

I still like pencil schematics, fast and easier ... schematic tools are nice for presentations and PCB outsource work, but less for works in progress and hacking!

sure, but when they start to be more complex (like whole DSO) you lose the game. I just finalized (first turn,
will check again all connections just due complexity) FPGA/SRAM/DRAM/NAND/SoC section of HanTekway DSO
schematic, without proper schematic tool i would get crazy.

[A Hellene]

Well, this is how it is: I have had a 256GB Crucial M4 SSD (a real rocket!) in my hands for almost a month, watching it collecting dust in a corner of my office, impatiently awaiting to see what this babe can do in my three years old PC box (one of the first eight-threaded quad core Intel i7 920 with blazing fast triple-channel memory of the lowest possible DDR3 latency, overclocked everything, including the buses, at 135% and going strong on a 24/7 basis since the time it was assembled!).

Since my system was very well tuned, I was extremely hesitant to be setting up again and configuring everything (the OS plus the programs plus their data plus their settings plus -you name it) from scratch, for the next ten days or so; I usually set up the system once, only when I change the motherboard or the OS. If I was running WinXP x64, migrating the whole system to a new HDD would be like going for a walk in the park; but Win7-x64 ostensively refused to copy the whole setup to a HDD of a different serial number! Thank you, again, M$... Anyway, I finally managed to migrate the system successfully to this blazing-fast SSD and the results were more than satisfactory; they were beyond any expectation! Even though I had my previous system installed on a Black-family Western Digital HDD (one of the fastest and most reliable commercial-grade drives with 5 years warranty)! I was amazed with the unexpected responsiveness my three years old system reacts to any of my commands, after the installation of the aforementioned SSD!

Well, I guess that now it is time for me to play with my other toys; and the forgotten and dismantled DS1052 came to my mind! I have purchased fresh flux and solder paste to reflow (meaning to de-solder, clean up, re-ball with 62/36/2 solder, and finally re-solder in place) the BGA package! But I am hesitating to do it because I know that I will be tempted to leave the FPGA un-soldered untill I draw the schematics of the digital section, as well...

You see, the thing for me is the nostalgia trip regarding the "old days" when I was hand-drawing everything; and I was raised with OC71's and AC126's! And, from the schematics I have published, I think that it is most obvious to the experienced eye the fact that it has been eons since I grabbed a real pencil for the last time and started penciling lines on a piece of blank paper! You see, though I used to be a calligrapher, I have not touched a pencil since the very early '90s, when my very first CAD software was a (paid) version of the QuickRoute Pro, just before I met with the the 32-bit Protel for Windows v1.5 (for Windows 3.1) that came in 2+4 1.44 floppies: Ahh, love at first sight! It is the DOS-ish flavor that I cannot stand in Eagle, for example, one of the remains of those days...
Halcyon days indeed!


-George

[A Hellene]

This is a minor update, since there has been some progress done --despite the lack of my spare time.

I am sorry though for the quotes that follow but I have already written the following down in a similar thread:

Ah, do not worry, tinhead! Copy mistakes are in order when reversing even a single-side PCB --not a six-layer one!

For example, I have also spotted a couple of these errors in the Rigol schematics I have posted: The Comparator Hysteresis driver in the "DAC, Demux, Sample & Hold and Buffer" sheet actually is a driver with a 5V0 to 3V3 level-shifter section implemented. By the way, I have de-soldered, cleaned-up and re-balled the Cyclone III FBGA chip, and when I will find some spare time I will draw the digital schematics sleets, too! You see, Rigol has a couple more DAC output signals (a 500.00mHz triangular (not sawtooth) waveform output and a waveform_start(?) signal extra circuitry that do not make any sence to exist in the analog section) that cannot be traced anywhere in the PCB; so, I removed the FPGA to see if these "blind" signals are fed into the Cyclone III.

Though I have not reversed the digital section of the Rigol yet, I think that the Lattice LUT (as well as the CLPD in your device) are RAM address lines generators for the FPGA configuration (which does not seem to have a dedicated address bus for the config. memory, so it probably clocks an external address-bus generator) and the BlackFin that cannot address the 22bit-wide boot-up Spansion FLASH memory alone because it has a 20-bit wide address bus hardware. But I could be wrong; I cannot really tell until I fully reverse the PCB...

What?!?
I am curious to know how do you do that?

With patience!

I think is is time for a short tutorial on the BGA and Flat Pachage rework process, using home equipment:

Equipment used: A hot-air rework station, a soldering iron, soldering wick (ERSA 2mm/3mm/4mm wide), flux paste (I prefer the RMA flavor but I've only found a no-clean syringe container at the local stores -that is fine for this job), SMD rework solder-wire (sub-millimeter Alpha-Fry 62/36/2) and flux soldering paste (EDSYN 62/36/2 no-clean).
Remember that the activated flux (RA/RMA) based products have only a few months self-life, even if stored in the refrigerator.

This is the rework strategy:
1. Preheat the PCB using 130 degrees hot air for 2-3 minutes, to avoid any thermal expansion artifacts,
2. Use conventional (kitchen) aluminium foil to protect the surrounding components, by cutting off a small window to expose ONLY the target chip to the hot air flow,
3. Desolder the BGA using 300..320 degrees hot air, remove the chip and wait for everything to cool down,
4. Clean the old solder, holding the BGA package in a small plastic vice using solder wick and lots of flux; always clean the used flux (I use medical alcohol of 95 degrees or better),
5. Clean the PCB, as above,
6. Reball the BGA with the soldering iron, Ag-containing solder-wire (I use 62/36/2) and lots of fresh flux; always clean the used flux,
7. [Optional step] Reverse the PCB (that takes tiiiiiiime...),
8. Reball the PCB pads as well, as in step (6), since chip re-balling has not provided the pads with enough solder,
9a. Carefully apply flux soldering paste on the PCB pads only and flux at the chip pads, or
9b. Apply flux in lack of flux soldering paste,
10. Carefully place the BGA package on the PCB (in a single move, if possible) and
11. Preheat the whole PCB area around the chip using 130 degrees hot air for 2-3 minutes,
12. Raise the hot air temperature at 280..300 degrees and apply it to the chip in a slow circular motion,
13. Wait for the molten solder surface tension to move the chip in place when the solder melts,
14. Tap the chip gently towards the PCB, to make sure that all its pads are in contact with the solder underneath,
15. Remove the hot air and wait for everything to cool down naturally (by themselves); always clean the used flux, and
16. Done! Power the device up.

Right now I am at the seventh step...


NOTE: It is not as difficult as it sounds to be; but you need to practice enough before daring to touch your actual device without destroying it!

A second note is about the chip size: As a rule of thumb, use a hot air nozzle of half the diameter of the chip size. For chips smaller than 20mm x 20mm you may skip the PCB preheating step, only if the PCB is very thin. Unfortunately, this is not the case with Rigol's mainboard.

A third and very important note: Always know what you are doing. Always use your common sense! Miracles happen only in fairy tales...

Finally, remember that a good tool is NEVER expensive enough to have it. Just consider the possible extra cost of a damage done by using cheap ("affordable" in the marketing jargon) tools...


-George

[IanB]

Remember that the activated flux (RA/RMA) based products have only a few months self-life, even if stored in the refrigerator.

Do you refer here to solder paste specifically, or to other solder/flux products too?

Correspondingly, do you imply that no-clean flux solder paste has a longer shelf life than the RA/RMA based product?

[A Hellene]

According to the datasheets of the products I use, I have never seen any mentions about the self-life of the no-clean fluxes, with the exception of the no-clean solder paste that has no more than six months self-life.

I am under the impression that the RMA fluxes have a typical self-life of a couple of years, and the RA ones even less. Additionally, I think that most, if not all, of the soldering wires have non-activated rosin (R) flux cores.

Are you aware of any no-clean flux products (with the exception of soldering paste) that have limited self-life?


-George

[IanB]

I have solder wire with RA flux and also some with no-clean flux. I do not know how to choose between them so I have tended to pick the RA flux. Apart from solder wire I also have some different containers of rosin paste flux and rosin liquid flux. The liquid flux says RA, the paste flux just says "rosin".

I have always thought that flux cored solder wire and rosin flux would last indefinitely. I have certainly seen rosin flux that still seems to work after many years of storage, although the paste flux can apparently dry out if not kept in an airtight container.

I have never used solder paste, but I have heard many people tell it has a short shelf life. I was therefore interested when you seemed to mention that no-clean solder paste might not have such a limitation. Apparently though, it doesn't, and all solder paste needs to be used within a short time of purchase.

[flolic]

6. Reball the BGA with the soldering iron, Ag-containing solder-wire (I use 62/36/2) and lots of fresh flux; always clean the used flux,
7. [Optional step] Reverse the PCB (that takes tiiiiiiime...),
8. Reball the PCB pads as well, as in step (6), since chip re-balling has not provided the pads with enough solder,

I tried that method few times, and while in general that works, I was never really satisfied with it. So in the end I purchased various size solder balls and direct heat stencils and that works so much better and quicker.

14. Tap the chip gently towards the PCB, to make sure that all its pads are in contact with the solder underneath,

Be veeery careful doing this because any excessive pressure/movement of chip will displace molten solder from pads and squeeze it out, create shorts and various other nasty problems. Remember, we are talking of allowed tap motion of a fraction of millimeter! I learned that hard way despite being very careful...
So I don't do that any more, and simply let gravity do the job.
Also, when using reballing method with solder balls and stencil every ball is exactly the same size. When you heat up the chip and PCB to the solder melting point, you can see the chip "drop" as the balls melt and collapse.
I done that so many times with 100% success... 

[A Hellene]

Ian,

Thank you for the information. I was confused about the rosin and the resin based fluxes. After looking that up, it seems that the only difference between them is that rosin fluxes are based on the natural pine tree rosin and the resin ones are based on synthetic or modified rosins...

I was mostly using resin flux paste but switched lately to liquid synthetic flux, which seem to be more efficient but its residue is stickier and more difficult to be removed with alcohol. A three years old ERSA liquid no-clean flux I still have seems to be working as it did when it was purchased. The mildly activated flux (RMA) seems to be ideal for manual soldering, since it is even stronger and easier to remove. I have no experience with the activated (RA) fluxes, though.

Until recently, I used to solder the flat packages with the soldering iron; but it was a pain to de-solder them. The hot air rework station solved this problem for me and made soldering even easier; but it requires better ventilation. Using solder paste has been a fairly new experience to me and I really like the way it works. It is very easy though to short any neighboring pins if not applied carefully; but it does not really take long to become familiar with. The solder paste limited self-life does not became an issue by purchasing smaller quantity packages (e.g. 10g product in syringe).
_____



flolic,

Thank you for sharing your experience! Yes, I am aware of the dangers you mentioned. Re-balling with the stencil method is ideal; doing it manually, the secret is to apply the same amount of solder everywhere!

This can be done by applying smaller solder balls to both the chip and the PCB pads. By re-balling each pin individually, some pins will receive more solder that the others. This can be prevented by pouring solder to the pads by steadily dragging the soldering iron tip along them all, and not insisting on each one of them. With plenty of flux, of course. If there is not so much solder, it becomes safe to gently tap the chip towards the PCB, as a last move to ensure the sitting of all its pads.


-George

[IanB]

I've just discovered after doing a bit of investigation that no-clean flux and rosin flux (R, RMA or RA) are variations of the same thing. The no-clean flux is a kind of RA flux with very similar properties. Neither RA flux nor no-clean flux need to be cleaned from a finished board to prevent corrosion, but they may need to be removed for appearance sake or to allow conformal coating.

On the other hand, water soluble flux is totally different from rosin flux, and this flux residue must be completely removed from the board after soldering by thorough and complete washing with water or a suitable solvent.

A general trend and recommendation for both home build and industrial users is to avoid water soluble fluxes and prefer rosin type fluxes, especially including solder paste and SMT applications. This is because water soluble flux residues may get trapped under SMT components where the washing process cannot reach them, and in that case corrosion from the aggressive flux residues may cause trouble down the line.

Although RMA type rosin fluxes might seem milder, my reading suggests no great concern about leaving RA flux residues behind. One may as well use RA flux as it is likely to work better on dirty or oxidized surfaces.

[Lightages]

All this soldering and BGA information is very useful, very much more useful in its own thread instead of buried in a thread about the performance of the DS1052E.....

I know that it is inevitable that a thread always gets sidetracked or hijacked but this is really mixing things up. I was hoping that we would see less threads going off track in this forum. Humans will be humans I guess 

[IanB]

I'm sorry. I was thinking of this when I posted it, but unfortunately threads are not the best way to organize information. What forums really need is keywords and labels the way Google mail has it. For me, I always resort to search tools when I want to find stuff...

[IanB]

I have started a new thread on solder fluxes in the technical info section.

[A Hellene]

Ian,

Thank you for the quite interesting pieces of information you posted. I was already aware of the water soluble fluxes aggressive corrosiveness. But I was under the impression that the fully activated (RA) rosin flux was also corrosive. Having no further investigated about the no-clean fluxes, other than just reading the data sheets of the specific products I used or randomly selected other ones in comparison, I was avoiding the RA fluxes as well.

I used to have as a generic guide a piece written in 2003 by Colin O'Flynn, a member of the AVRFreaks community I am also a member of. Let me cite a few of his words, regarding the differences between the Kester Rosin flux RMA 186 pen (Kester PN. 83-1000-0186) and the Kester Rosin flux 951 no-clean pen (Kester PN. 23-6337-8806):

The flux is very very important. It comes in pens, which makes applying the flux very easy. The pen's have a shelf life of 2 years, so they should be good for a while. The lower the number with the flux the more active it is. As a flux's activity increases, it normally makes soldering easier as it resists solder bridges more. If the activity is high enough though you MUST clean the flux off the board or it will eat the board away. The RMA 186 flux is nice in resisting bridge's, but it doesn't need to be cleaned off the board. Some applications might need you to clean it though, and to do that you can use rubbing alcohol and some sort of brush or swab. The 951 no-clean is designed to not need cleaning off the board. If you need a high-impedance application or very sensitive boards you will probably have to clean it anyway. The 951 doesn't resist bridges as well though. Will discuss which one to apply later.
[...]
IC's are slightly harder than the two-pin devices, but not too bad. However first we have to discuss the flux pen. You can use either the 186 RMA or the 951 noclean. If you will be doing a fairly fine lead pitch the 186 would probably be the better choice. If you don't need as an active flux because you will be doing a fairly large pin pitch you can use the 951 flux. For example the TQFP package will benefit from the 186 flux, but a SOIC package might not need the 186. However if you only want to buy one flux pen it should probably be the 186 as it is more universal.

Emphasis in mine.

Regarding sidetracking/hijacking of this thread, this in not the case to me, therefore there is no need for apologies. On the contrary, the information contributed is essential and absolutely in line with the subject matter of this discussion, which is now about the reverse engineering of a PCB suspected to be faulty. Please, feel free to pop in at any time!
_____


Lightages,

Thank you for your concern. You described it very well, yourself: It the human nature factor that makes the progress, after all!

Please, feel free to quote any parts of my messages (since I can only speak for myself) you like or find interesting enough in order to contribute, either by adding to the conversation or by summurising them in an existing or in a new discussions thread.

After all, what we really do is exchanging views!
_____


Squonk,

Do not worry, my friend! Things will take their natural course, since it seems that we have a lot of cultivated, educated and caring people over here.

Furthermore, I would invite our host, Dave, to add to rather than subtract from this discussion!



-George

[A Hellene]

I think I should quote a couple of additional views I have exchanged with tinhead about the manual BGA reballing technique, since his solution is superior to this I described in the BGA/FP rework mini guide I published yesterday:

ahh, you using the ugly method (self-made "balls"). I tried it once, for K4S561633F because i didn't had right balls here.
The first run was "disaster" (because of the DIE encapsulat in the middle or the RAM chip), second run was finally working - few weeks later this board started to crashing so i had to resolder again (with proper balls), since them (more than a year) the board is working (24/7).

Therefore i can only say, buy proper balls, they didn't cost that much to risk the FPGA. Sure the best is to have reballing set with stencil to place balls, but believe me, even without stencil you can easily place them one by one.
Just put a bit of flux on FPGA - note too much and they will "swim" away, to less and they will not stay in place when using hot air - better is to use IR (or whatever oven for reballing) - watch them careful during this process, when one starting to move around remove it and place new one (with tweezers or preheated soldering iron).

Thank you, tinhead!

This is a great idea! Re-balling manually the BGA chip with standard solder balls is the best solution, in order to have a homogeneous and uniform solder quantity on every pad! Without even the need of the special stencil equipment!

All I will have to do is to wait for the local stores to open after their summer break; or, to place an online order. But, something tells me than I may have not yet finished reversing the PCB...

Anyway, your idea is marvelous! Thank you, again, for the solution you gave me!

It seems that this is not only a better solution but an easier to implement as well!
Thank you, tinhead!

-George

[IanB]

Thank you for the quite interesting pieces of information you posted. I was already aware of the water soluble fluxes aggressive corrosiveness. But I was under the impression that the fully activated (RA) rosin flux was also corrosive.

I believe at this stage one must move from the general to the specific, since not all RA fluxes from different sources might have the same properties. The RA flux in my possession comes from MG Chemicals, and this is what they have to say about it:

Liquid Rosin Flux 835

For leaded and lead free soldering. Fully activated. Offers superior fluxing ability. Instant wetting. After soldering, the rosin residue is non-corrosive, non-conductive, moisture and fungus resistant.

Although they do not call this a no-clean flux, I infer from their description that there is no specific requirement to clean off any flux residues left behind after soldering.

[A Hellene]

Ah, yes, I see. A lot of more specially formulated products, not necessarily closely related to other ones of the same category.

Incidentally, what I have lately purchased is their No-clean flux paste 8341, whose also "the residues do not need to be removed for most applications."


-George