<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">Am 22.02.2017 um 15:49 schrieb H. Nikolaus Schaller <<a href="mailto:hns@goldelico.com" class="">hns@goldelico.com</a>>:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class=""><br class="">But now the bad news.</div><div class=""><br class="">-1.: Only 12 out of 36 (*) GTA04A5 boards we<br class="">have produced, are booting to Linux. The others either have a</div><div class="">short circuit under the OMAP (which is the general PoP soldering<br class="">problem we already know since the first generations of the</div><div class="">GTA04) or the OMAP shows no response or does not recognise the</div><div class="">µSD card for unknown reasons.</div></div></div></div></blockquote><br class=""></div><div><div style="font-family: monospace; font-size: 11px;" class="">Because we are a community to share experiences and some people</div><div style="font-family: monospace; font-size: 11px;" class="">expressed (unfortunately not here) the question how Nokia was</div></div><div style="font-family: monospace; font-size: 11px;" class="">obviously able to build the N900 or N9 and doubt the warpage</div><div style="font-family: monospace; font-size: 11px;" class="">effect, let me write down some of the thoughts:</div><div style="font-family: monospace; font-size: 11px;" class=""><br class="">* we do not know how much scrap others do or did produce (such info</div><div style="font-family: monospace; font-size: 11px;" class="">is usually not shared with the public), so our 30% yield may</div><div style="font-family: monospace; font-size: 11px;" class="">be equally good. Or may be worse. Since it is >0 cases you only</div><div style="font-family: monospace; font-size: 11px;" class="">see the successful results in the wild.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">* most likely, they were allowed to scrap 1000 units at a total value</div><div style="font-family: monospace; font-size: 11px;" class="">of let's say 300k€ to learn the process and then they were able to</div><div style="font-family: monospace; font-size: 11px;" class="">build 1 million units at high yield. We simply don't have that</div><div style="font-family: monospace; font-size: 11px;" class="">much money for experimentation with the production process. I.e.</div><div style="font-family: monospace; font-size: 11px;" class="">we want to win champion's league but can't afford to do the complete</div><div style="font-family: monospace; font-size: 11px;" class="">training.<br class=""></div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">* there are subtle variations between the chips. Basically the OMAP</div><div style="font-family: monospace; font-size: 11px;" class="">is a tiny 0.1mm PCB where the Silicon die is sitting in the middle.</div><div style="font-family: monospace; font-size: 11px;" class="">The thickness of this PCB has a big influence because it is soft outside</div><div style="font-family: monospace; font-size: 11px;" class="">of the Si-chip and the exact size of the Si-chip also has an influence</div><div style="font-family: monospace; font-size: 11px;" class="">because it makes this PCB stiff in this area. TI did shrink the DM3730</div><div style="font-family: monospace; font-size: 11px;" class="">compared to the OMAP3530 and made the PCB thinner. So it is a completely</div><div style="font-family: monospace; font-size: 11px;" class="">different thing wrt. thermo-mechanical effects.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">* the PoP-RAM chip sits on top and has a hard plastics case and does</div><div style="font-family: monospace; font-size: 11px;" class="">not warp, but modifies the way the lower chip gets heat and how far</div><div style="font-family: monospace; font-size: 11px;" class="">it can move until the upper side of the Si-die touches the bottom of</div><div style="font-family: monospace; font-size: 11px;" class="">the PoP-RAM and starts to lift it off. Even the exact material of the</div><div style="font-family: monospace; font-size: 11px;" class="">BGA balls of the PoP-RAM can have an influence how much they "pull upwards"</div><div style="font-family: monospace; font-size: 11px;" class="">the DM3730 carrier PCB. Or press down the Si-Chip onto the PCB.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">* due to this special construction the BGA balls under the OMAP die</div><div style="font-family: monospace; font-size: 11px;" class="">behave differently than the BGA balls where no die is above. The effect</div><div style="font-family: monospace; font-size: 11px;" class="">is that we either have shorts or open joints in the inner or outer ring.</div><div style="font-family: monospace; font-size: 11px;" class="">Finding a compromise between Scylla and Charybdis, where we have neither</div><div style="font-family: monospace; font-size: 11px;" class="">shorts nor open joints, is the key to high yield. It looks (really looks</div><div style="font-family: monospace; font-size: 11px;" class="">in X-ray) as we simply have not yet found the best compromise and now ran</div><div style="font-family: monospace; font-size: 11px;" class="">out of money and components during this search.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">* it looks as if the iMX.6-PoP chips use a hard plastics case for the</div><div style="font-family: monospace; font-size: 11px;" class="">processor - so that it can't warp at all and all BGA balls on the lower</div><div style="font-family: monospace; font-size: 11px;" class="">and upper end have the same mechanical background. So one could say we</div><div style="font-family: monospace; font-size: 11px;" class="">fight with a design weakness of the DM3730 package design. To be fair it</div><div style="font-family: monospace; font-size: 11px;" class="">must be said that the PoP stack of the DM3730 appears to be thinner than</div><div style="font-family: monospace; font-size: 11px;" class="">the iMX.6 which might be crucial to squeeze the PCB into a smartphone</div><div style="font-family: monospace; font-size: 11px;" class="">case without making bulges.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">* and not to forget: we don't have 0% yield, like it would happen with</div><div style="font-family: monospace; font-size: 11px;" class="">a simple software or hardware bug. Those are usually show-stoppers and</div><div style="font-family: monospace; font-size: 11px;" class="">when fixed, it goes perfect afterwards. We have 30% yield. This means that</div><div style="font-family: monospace; font-size: 11px;" class="">production is possible, but just too expensive for us to find and eliminate the</div><div style="font-family: monospace; font-size: 11px;" class="">final disturbing factors. So it is mainly a financial limitation we have.</div><div style="font-family: monospace; font-size: 11px;" class="">If the community can afford to pay 1500€ for each GTA04A5, we can start over</div><div style="font-family: monospace; font-size: 11px;" class="">tomorrow. So one could even develop a crude view that the bug is that the</div><div style="font-family: monospace; font-size: 11px;" class="">community can't afford what we are doing. Well, I have no idea how to fix</div><div style="font-family: monospace; font-size: 11px;" class="">such a bug... Would be nice to learn.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class="">* others failed as well with this or similar combinations. For example</div><div style="font-family: monospace; font-size: 11px;" class="">the OpenPandora was initially planned to be built in the US by the same</div><div style="font-family: monospace; font-size: 11px;" class="">production line as the BeagleBoard was built. But if you ask Pandora owners,</div><div style="font-family: monospace; font-size: 11px;" class="">they will tell you about the pain when it initially failed.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class="">* we then suggested to ED to go to the production company we now have used as well,<br class="">and the OpenPandora 600MHz (OMAP3530) was successfully built. When they switched</div><div style="font-family: monospace; font-size: 11px;" class="">to the 1GHz Pandora some problems came back again, but were solved again. What we</div><div style="font-family: monospace; font-size: 11px;" class="">also have to consider is that during this time people have changed and machines</div><div style="font-family: monospace; font-size: 11px;" class="">were upgraded which is a process that usually looses some knowledge or has to</div><div style="font-family: monospace; font-size: 11px;" class="">be regained for a modified situation.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class="">* for the GTA04A3/4 we also had to fight the same issues at a different production</div><div style="font-family: monospace; font-size: 11px;" class="">site. And after a long learning curve it worked better. You may ask why we didn't</div><div style="font-family: monospace; font-size: 11px;" class="">choose them again. Well, they knew about the low yield problem and they would have</div><div style="font-family: monospace; font-size: 11px;" class="">asked for much more money for trying production again without warranty...<br class=""><br class="">So it is like soccer. You know all rules, you know the dimensions of the goal, the</div><div style="font-family: monospace; font-size: 11px;" class="">ball and the shoes, the playground and that the grass is green. You also know your</div><div style="font-family: monospace; font-size: 11px;" class="">players - but making a goal is not at all guaranteed by this knowledge. It needs</div><div style="font-family: monospace; font-size: 11px;" class="">training and luck.</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div><div style="font-family: monospace; font-size: 11px;" class="">Hoping this big bunch of experience helps other projects to succeed,</div><div style="font-family: monospace; font-size: 11px;" class="">Nikolaus</div><div style="font-family: monospace; font-size: 11px;" class=""><br class=""></div></body></html>