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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Strange things ocuring during reflow...

Views: 7054

#61143

Strange things ocuring during reflow... | 17 February, 2010

Hi there: During the past weeks (let's say since beginning of the year) we've been experiencing some issues with shifted components. We verify for position before Reflow oven and the components are Ok, but they observe shifted after reflow. it occurs in one or two References, but the part is placed more than that (some of them are 14 placements). we have been seeing this on different boards, same part numbers on each boards (mainly resistors and a SOT-23). It is occurring only in one Oven, we use Solder paste NC-SMQ92J SnPb process and use RTS Profile. Also operators called me yesterday saying that solder on test points are "jumping" or blowed off the test point. This could lead me to think that solder paste is involved, but I also need to consider any other thing (maybe component or oven). we have been trying rotating PCB 180º without improvement.

Any thoughts?

Attachments:

reply »

#61146

Strange things ocuring during reflow... | 17 February, 2010

Is your oven adjusted correctly for temperature and blower and conveyor speed?

reply »

#61147

Strange things ocuring during reflow... | 17 February, 2010

> Is your oven adjusted correctly for temperature > and blower and conveyor speed?

As far as blower settings it only has a Hi-Mid-Low setting (is a heller 1809), and we have been working with all at Hi speed since line was started (1.5 year ago). Conveyor speed is about 30 in/min, I have measured time of a board passing through oven and seem to be OK, oven never has been calibrated or something. I will run a profile and see what the results are.

thanks for the replay

reply »

#61148

Strange things ocuring during reflow... | 17 February, 2010

We understand what you're saying about the settings, we wonder how the actual compares to the set point.

reply »


JAX

#61149

Strange things ocuring during reflow... | 17 February, 2010

Did you just change anything on the Exhaust?... even if the change was adding something else to the main exhaust trunk, if you don't have each item seperated. Although CFM changes should not effect the Blower Speeds or the Zone stablizing time, since the exhaust is used to pull air from the beginning and end of the oven... creating an "Air Curtain", I have seen the same side effects.

reply »

#61154

Strange things ocuring during reflow... | 18 February, 2010

thanks for your replies, I will check about oven integrity (calibration) and any exhaust issue... as fas as I know there's not change or addition to exhaust system but I need to confirm.

reply »

#61155

Strange things ocuring during reflow... | 18 February, 2010

I have also seen on Heller ovens (even new ones EXL series) cross profile temperature differences over their spec of +/- 3 deg C, sometimes up to 7-10 deg C, 200-230mm from fixed rail. This can cause funny issues , profiling can cover this up and not be seen.

reply »

#61158

Strange things ocuring during reflow... | 18 February, 2010

An air temperature tolerance of +/- 3 deg C along a 200mm width would not play a significant role on the board's temperature due to its thermal mass. However if the air temperature varies by 10C along the conveyers width, I can see how a 5 degree variation on a PCB can affect solder joint quality. Especially if the peak is on the low end (230-235C)

reply »

#61171

Strange things ocuring during reflow... | 19 February, 2010

Read my article in this month's (Feb 2010) issue, in it I describe the reason so many companies are seeing their DPMO climbing. Richard Stadem

reply »

#61172

Strange things ocuring during reflow... | 19 February, 2010

I'm sorry, make that this month's issue of Circuits Assembly magazing. Richard

reply »

#61175

Strange things ocuring during reflow... | 19 February, 2010

I have a debate here with Facilities maintenance dept.

oven is asking for 550 SCFM and they are measuring 770CFM I know that is different SCFM to CFM... but I don't know the pressure.

any thoughts on how to convert???

reply »

#61177

Strange things ocuring during reflow... | 19 February, 2010

Vent monitor, look here: http://tiny.cc/LIY8k

reply »

#61183

Strange things ocuring during reflow... | 19 February, 2010

Nice one the baseball glove trick, but my boss wasn't in the mood for that (it wasn't even funny to him...) anyhow convection turbines were checked on the oven and they found that the bearings on the motor was too loose, then 2 motors were replaced, zones 7 and 9 upper side (I think this was an issue with Heller MKZIII generation) but we need to evaluate results.

Best regards from the most violent city in the world (not so proud of that part) Juarez, Mx.

reply »

#61188

Strange things ocuring during reflow... | 21 February, 2010

Dean: Are there limitations to the size or configuration of component that can be retinned and rereeled?

reply »

#61223

Strange things ocuring during reflow... | 24 February, 2010

Hi! Just to update... we checked along with solder paste suplier and found that the curtain on the oven was probably causing the issue so we removed in order to troubleshoot, as far as I know this curtain helps to not allow to flow oxygen into the oven while having N2 environment... we're evaluating and seems to be the root cause.

anyways it is telling me that my cooling is not so good.

Attachments:

reply »

#61242

Strange things ocuring during reflow... | 25 February, 2010

Good question, the answer as of right now is yes. Our machine is only able to go down to 0402 parts before the surface tension of the solder begins to cause issues with maintaining the placement position of the part on the nozzle. However, we are developing small fixtures (Auer boats) that will be loaded and then the Auer boat can be used to dip a number of tiny parts all at the same time. The Auer boat fixtures are then used to run the parts through a machine wash so they are effectively tinned and washed in bulk, and then picked and placed at high speed out of the fixture into a new tape, waffle tray, or whatever feeder we wish to use.

reply »

Reflow Oven

reflow oven profiler