We as usual I have to agree with Dave Hillman and Richard Stadem.  The point that Joyce made about nitrogen allowing you to lower the Tp a couple of degrees an make minor changes to the reflow profile are correct and they may have a very minor impact on warpage but to the best of my knowledge the impact wouldn't be large enough to measure much less make a difference.  All of my experience with condensation reflow soldering (i.e., vapor phase) was before BGAs so I don't have any direct data but vapor phase is a much more uniform heating process and would therefore have an impact on board and part warpage and might be helpful but  I don't think you would have to run a trial to see if it would be helpful enough.

George

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
Sent: Monday, January 23, 2017 2:54 PM
To: [log in to unmask]
Subject: Re: [TN] Nitrogen Reflow and Warpage Issues on POPs

Hi Bob - in our testing, the package preformed better using a lead-free temperature reflow profile - we had much less warpage and other associated temperature impacts which we attributed to the package designers optimizing their package construction characteristics for a lead-free reflow temperature profile (its a lead-free part, so most frequent use would be in a lead-free process). We were using a 12 zone oven so lots of room to profile creation - how many zones in your oven?

As for VP - I have never put a BGA in a VP process yet. It should work provided the condensing VP fluid doesn't cause the BGA to physically move.

Dave

On Mon, Jan 23, 2017 at 1:48 PM, Bob Wettermann <[log in to unmask]> wrote:

> Hi Dave:
>
> This is SAC process.
>
> For rework we have tried to go "backwards" to Sn63 to reduce max temp. 
> The results were better. Customer did not want to go throiugh the rel 
> testing reqts of a bismuth-based alloy.
>
> Any thoughts on using a vapor phase reflow instead?
>
> BWET
>
> On Mon, Jan 23, 2017 at 1:29 PM, David Hillman <david.hillman@ 
> rockwellcollins.com> wrote:
>
>> Hi Bob - I have done process compatibility testing with the TI OMAP 
>> BGA and the use of a inert atmosphere has no impact on the warpage 
>> characteristics of the package (been there, done that, have the Tshirt).
>> Are you using a tin/lead soldering process or a lead-free soldering 
>> process? POP technology was "born" in the lead-free era and as such, 
>> that package isn't a fan of a tin/lead soldering profile.
>>
>> Dave Hillman
>> Rockwell Collins
>> [log in to unmask]
>>
>> On Mon, Jan 23, 2017 at 11:29 AM, Bob Wettermann <[log in to unmask]>
>> wrote:
>>
>>> Dear Technetters:
>>>
>>>
>>>
>>> We have a Class 3 customer with very complex, high density 
>>> placements (think cell phone for the military). This board is laden 
>>> w/0201s, 0.4mm pitch BGAs, shields, mirrored BGAs and the TI Omap POP (0.4/0.5mm pitch).
>>>
>>>
>>> The problems in this board assembly for some time have been isolated 
>>> to this OMAP part.  We have lots of shorts and opens 
>>> (randomly-spaced) as confirmed by electrical testing, dye and pry 
>>> and cross sectioning. The Omap has been shown to warp 5-7 mils 
>>> depending on the reflow profile.( It is a no clean SAC305 process). 
>>> We have profiled the reflow process by embedding TCs in the corners 
>>> of the balls of the device (ball interface with the board where all 
>>> of the problems are) , the die,  neighboring components etc. We 
>>> dialed in the profile as low of a temp as possible.
>>>
>>>
>>> We are running several DOEs to come up with a placement/rework process.
>>>
>>> As part of the investigation the client is fixated on nitrogen 
>>> reflow being part of the solution to these warped BGAs. Nitrogen 
>>> reflow IMHO is the solution for joint aesthetics, wetting issues and 
>>> enhanced reliability of the interconnection.
>>>
>>>
>>> ? Does anyone have experience with hot air reflow using nitrogen 
>>> where its addition helped to mitigate warpage issues?
>>>
>>>
>>> Thanks!
>>>
>>>
>>> --
>>> Bob Wettermann
>>> BEST Inc
>>>
>>
>>
>
>
> --
> Bob Wettermann
> BEST Inc
> [log in to unmask]
> Cell: 847-767-5745 <(847)%20767-5745>
>