Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Multiple reflows

Views: 3076

#68059

Multiple reflows | 31 January, 2013

Hello folks,

we would in certain cases run a PCB second time through reflow. I never trusted a board that is reflowed multiple times and I wonder am I really right? Can we reflow boards multiple times? What are the limits? Does it depend on the PCB material, finish, solder paste? I would really like to see your knowlwdge and thoughts on the subject.

reply »

#68061

Multiple reflows | 31 January, 2013

Are you talking about double sided reflow or just multiple passes for one side? If you're running multiple passes for one side, why?

reply »

#68064

Multiple reflows | 31 January, 2013

Let's say I have an open joint on a BGA and I want just to reflux it and rerun the board.

reply »

#68071

Multiple reflows | 1 February, 2013

If you have a hard-gold on your pads, it's not a problem. Hard gold can give to you 4 or 5 times for PCB soldering (BGA repair).

Soft gold (or flash-gold) can destruct, after that will start a migration of nickel up through gold, your pads will be a black and you can't solder anything to this pads. The same situation with HASL (not every time, but it is better not to risk).

reply »

#68073

Multiple reflows | 1 February, 2013

Regardless of the surface finish, you should try to limit the reflow cycles to 3 with no more than 5 at most. This includes reworking a BGA site as well. Remember that heating/cooling to remove a BGA is one cycle and heating/cooling to place a BGA back on is a second cycle. Check out #6 on this IPC Outlook webcast for more information.

http://www.ipcoutlook.org/webcasts/50341B.shtml

reply »

#68076

Multiple reflows | 1 February, 2013

Thank you guys. You keep adding valuable information here. I think we will try to stick with the 3 times reflow(if we count the BGA repair as 2 reflows). However sometimes we will run the board second time through the oven(just flux the suspect part infront) and if not working we will exchange the part(finishing with total of four thermal cycles on the same board).

reply »

#68077

Multiple reflows | 1 February, 2013

In agreement with Evtimov. Max 5 reflow cycles. Something like this scenario: Build bottomeside 1 Build topside 2 Reflow topside for suspect opens beneath BGA 3 Remove BGA during rework 4 Replace BGA during rework 5

Any convective rework after that, you are looking at an "engineering sample", or an oven profiling assembly. Just my $.02 'hege

reply »

#68082

Multiple reflows | 1 February, 2013

From some previous article I read (sorry, don't have citation), I think the main reason for limiting reflow count was due to via integrity.

reply »

#68130

Multiple reflows | 7 February, 2013

Thank you all for the input. There is another concern. Do you consider wave soldering or selective soldering as a thermal cycle too?

reply »

#68136

Multiple reflows | 7 February, 2013

I would consider wave solder as a cycle, in that for the most part the entire board is subject to the wave.

Selective Solder is a gray area in that regard, since you will be hitting one or more locations, that in total do not comprise a large percentage of the surface area of the board. Thats one of the areas where experience is your guide.

Unfortunately sometime the experience comes hand in hand with expensive mistakes..... I mean lessons... Just my $.02 'hege

reply »

#68140

Multiple reflows | 8 February, 2013

Hegemon,

my thinking was pretty much the same. I will probably not consider Selective soldering as a temp cycle. Thanks!

reply »

reflow oven profiler

Reflow Oven