New Oven Now Getting PCB Twist

2017/2/28 18:46:58

Hi All,

Pretty new here, and to the industry and doing my best to learn what I can. Sorry if this topic has been discussed extensively, but I couldn't seem to find it via a forum search.

Our company recently purchased a 7-zone reflow oven to replace our older 5-zone. Based on profiling our boards, our profile is falling within the limits of the solder paste and for the most part we appear to be getting good solder joints. However, the operator and supervisor believe there is significantly more bend/twist in our larger single-sided boards exiting the reflow oven than we had on the 5-zone.

One thing that stands out is the slope in the pre-heat stages is much higher now (pushing upper limits). Besides that, every other aspect seems to be about the same (Peak temp, time above 217, time between 150-217, etc). Would a higher slope during preheat be a factor contributing to excessive bend/twist of the PCB?

Also, they are telling me the amount of bend on double-sided boards is more than it used to be on the 2nd pass through reflow (board on rails), so I'm wondering what might be causing this as well.

I greatly appreciate any input/feedback I can get on this. Or, if anyone has a relevant link discussing this topic that would be great. Just for the heck of it, below is our basic profile on the 5 zone vs what we're using now on the 7 zone. Thanks again!

5-zone: Speed - 17cm/min Zone1 - 130C Zone2 - 170C Zone3 - 190 Zone4 - 240 Zone5 - 270

7-zone: Speed - 60cm/min Zone1 - 185 Zone2 - 190 Zone3 - 195 Zone4 - 200 Zone5 - 245 Zone6 - 255 Zone7 - 253

The technician helped us get the profile while doing the install of the 7zone, and at the time the bend/twist issue wasn't noticed and now we're trying to correct it. Oh, and this is a lead-free solder-paste. Thanks!