How to solder BGA chips without room for glue onto both sides of a PCB?

On Thu, 22 Feb 2007 20:15:58 +0100, Markus Zingg Gave us:

The word/term for today is "surface tension".

You have it done by professionals that can X-ray the resultant assembly. Period.

Errrr, so just because some professionals are suposed to do this, we are all not allowed to know HOW they do it?

I was under the impression that I wrote "I wonder how" and not "I want to solder..."

So, is there any kind soul out there willing to explain to me how it's done?

TIA

Markus

Well, my method is as follows;

Equipment needed:

1.) Hot Air gun 2.) Hot Plate 3.) flux pen 4.) Solder paste 5.) tweezers 6.) small peice of aluminum (optional)

Method:

Set hotplate so that the temperature is just below the solder melting point. Place the small piece of aluminum stock on the hotplate to keep the hotplate solderfree(optional). Prep the BGA chip by apply flux to the ballgrid pins. Apply solderpaste to pcb where the chip is going. Carefully set the BGA chip on the solderpasted pcb. Set the pcb on the hotplate. Aim the hot air gun about 6-12 inches from the chip. Watch the solderpaste melt. take the tweezers and touch the chip it should suck right in place due to capillary action. turn off hotplate and let the pcb cool.

HTH...

On Sun, 25 Feb 2007 10:39:49 +0100, Markus Zingg Gave us:

Do you have $200k for an X-ray machine?

On Sun, 25 Feb 2007 10:39:49 +0100, Markus Zingg Gave us:

Dumbass. READ THE POST. It is stated right there.

SURFACE TENSION.

On 25 Feb 2007 07:43:41 -0800, snipped-for-privacy@punkass.com Gave us:

NOT capillary action. That is what brings solder through a thru hole via.

SURFACE TENSION is what holds it on a surface mount assembly, nothing more. Nothing gets "sucked".

Well, there's both really.

Capillary action is the result of adhesion and surface tension.

The adhesive forces between solder molecules and the BGA are stronger than the cohesive forces resulting in a meniscus on the pcb pads and contribute to capillary action.

On Sun, 25 Feb 2007 19:47:38 -0500, maxfoo Gave us:

Yes, except that said action requires pathways, like a via or a via with a lead in it. On SMD, the ONLY force involved is surface tension, which by the way is the ONLY engine involved with capillary action as well.

On Sun, 25 Feb 2007 19:47:38 -0500, maxfoo Gave us:

There is no adhesive force in capillary attraction. The motion is due to surface tension. That is the engine by which capillary attraction works.

You are going to lose this argument. Surface tension is the model all SMD design has centered around since the very beginning.

And yes... it IS strong enough.

There's IMHO no reason to become offensive. I was reading your reply carefully including the two words "surface tension" but it was and still is too short for me to make all doubts go away.

I'm just not sure if surface tension is enough to solder chips to BOTH sides of a PCB which still is and was my original question. I'm well aware that surface tension is responsible for the chips to align propprely during reflow soldering. Maybe I'm wrong but so far I thought that either the chips have to be glued to the PCB (at least if they reside on the bottom) or else it can't be done. The question arose when I first looked at one of those high density 2GB PC memory modules where there are BGA chips on both sides of the PCB.

I simply figured that if one side of the PCB is solderd, those chips would fall off, or could be misaligned if the PCB is brought back into the oven with those already soldered chips on the bottom. I also could figure that the weight of the PCB itself would have a negative impact on the chips on the bottom and that there is special care needed if the chips on the bottom are different ones and not of the same height etc.

So either "SURFACE TENSION" is not everything there is to say about it, or then you are right but you then may understand now where I have/had my doubhts and alas why I ask again.

I don't care wether X-Ray equipement is $200K or $200 zillions. I just wonder how they do it for personal interest. Sometimes I just see something and wonder how it's done. I'm under the impression that this question is on topic in sci.electronics.basics. Please accept my apologies if not.

Could you or someone else therefore either confirm that even for soldering BGA chips to both sides of a PCB "surface tension" is enough or then eventually be kind enough to elaborate one the topic a bit more?

TIA

Markus

[snip] [snip]

Ok, I asked the same question in a german electronics newsgroup, and instead of getting answers like " You have it done by professionals..." and "period" and "dumb ass", they kindly explained that in fact the surface tension alone is strong enough to hold those chips on the bottom side in position during a second reflow even if the balls of the bottom side chips melt again.

I just thought to share this here for other potential "dumb asses" like me :-)

SCNR

Markus

On Tue, 27 Feb 2007 00:10:51 +0100, Markus Zingg Gave us:

You're the one that made the rule that it couldn't be glued on.

When you snipped, you snipped the "XXXX wrote" part, but whoever it was, I've filtered that person for being an offensive idiot.

This is sci.electronics.basics, where there is no such thing as a dumb question - it's here for beginners, after all, which each and every one of us was once (or still is, which is OK). :-)

Unfortunately, I have no idea how to solder a BGA. )-;

Good Luck! Rich

On Tue, 27 Feb 2007 02:45:52 GMT, Rich Grise Gave us:

Which is your forte.

Being an offensive idiot.

On Tue, 27 Feb 2007 02:45:52 GMT, Rich Grise Gave us:

There is a lot you don't know.