Hallo Leute,
Die Entwickler dieses OpenSource Projekts haengen mit BGA Bestueckungsproblemen fest:
Einer von ihnen (Walter) bat mich das unten beschriebene Problem mal hier zur Diskussion zu stellen, hat selbst keinen Zugang zur NG. Sehen ob jemand Ideen hat oder vielleicht gar einen guten Bestuecker bei Euch weiss der sowas hinkriegt. Ich kenne nur Bestuecker in den USA und Asien. Wer per PM antworten moechte:
hns goldelico.com (Dr. Nikolaus Schaller)
Ich bin kein BGA Experte (mag die Dinger ueberhaupt nicht) und konnte nur einen Vorschlag machen der hier mal bei aehnlichen Probleme geholfen hat. Habe ich ganz am Ende drangehaengt.
Hier der Text, ist was lang, Zitat:
Hi all, I did a long telephone call this morning to discuss the production situation of the GTA04A4 boards.
Am 25.06.2012 um 20:56 schrieb Dr. H. Nikolaus Schaller:
handful reworked GTA02)
Tour boards
So here is a copy of the latest X-Ray image of the DM3730CBP with short circuits:
If you want to compare to the GTA04A3 board X-Ray (with one short):
or the GTA04A2 board (where only 1 unit exists):
After analyzing and discussing the X-Ray images we now think we understand what happens (but you never know if you are right...).
The reason appears that the DM3730CBP gets some warp during the soldering process squeezing the balls in the middle of the BGA grid so that they may touch a neighbor and make a short circuit. And on the corners the balls lift off and this may result in interruptions.
This theory correlates exactly with the error patterns we see:
- some 50% of the boards come out of the soldering process with shorts on VDD1, VDD2 and/or VIO which are mostly available on the center balls
- if the chip has no short on the power supply or is reworked some
Now comes the crucial question: how can this be improved?
The specialists of the production company have spent whole weekends to do more experiments but did not yet find the right trick. It is not that they do not want to solve the problem (they see it as a challenge) they simply have not yet found the key.
One factor is that our GTA04 board has exceptionally squeezed components (since we must be small) so the soldering of a OpenPandora or the BeagleBoard may be a little easier from heat distribution.
I.e. we are pushing an experienced EMS to their limits... An EMS who has produced more than 2000 different products in small quantities (which is their strength) including some 0.4mm BGAs.
A new experiment is scheduled for week 29 to use a different reflow soldering machine and process which uses a little lower temperature.
Unfortunately, we can't contribute to this production improvement to speed things up.
Unless one of the readers on these list knows some real specialist for such PoP soldering of BGAs who is willing and capable to consult (even if it costs money). So if you know someone, please let me know.
So we had to decide to wait for the different reflow soldering process first.
So it is a stony path towards a community driven independently developed and produced open smartphone platform. But Rome wasn't built in one day...
And we have to solve this issue before we can start to think about a future quad core LTE device with multitouch... Please keep the faith.
BR, Nikolaus
Zitat Ende
... Mein Vorschlag war:
Das ganze sieht danach aus dass der Bestuecker mit BGA plus Feinleiter ein wenig ueberfordert ist. Das Temperaturprofil hinzubekommen ist nicht einfach. Auf dem ersten Bild sieht es so aus dass Kurzschluesse auch am Rand vorkommen. Ist total unueblich, aber mal so als Idee:
Wenn Ihr den Verdacht auf Woelbung habt und es weder ueber besseres Platinenmaterial noch besseres Temperaturprofil hinzubekommen ist, kann man vor dem Bestuecken in der Mitte und vielleicht noch an den vier Innenecken duenne Plastikunterlegscheiben aufkleben? Scheiben und Kleber muessten natuerlich mindestens ebensoviel aushalten wie FR4. Die sollten dafuer sorgen dass Balls nicht per lokal "zerquetscht" werden koennen.