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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Solder Skips

Larry Smith


Solder Skips | 17 March, 2000

We have just installed an omega wave to our W/S machine and are tring to W/S some of our bottom side surface mount components. I am still getting skips on some sot 23's. The component lay out meets all IPC 782 guidelines. I have verified these settings: Conveyor speed = 4.5 Dwell Time = 2.5 sec top side preheat temp = 175 F Solder contact area = 2" I have changed conveyor speeds, preheat temps, amount of flux being applied and wave height. I was told that changing the conveyor angle from 5.5 to 7 deg might help....any coments. Also what have others had the best results with a higher amplitude at the Omega wave ( Appox .030") or lower.

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Re: Solder Skips | 18 March, 2000

Larry: I'd like to see your angle increased generally and that could fix your problem. Lots of other things can cause skips, such as:

* Wave height, your might be high with 2" of contact * Flux contamination, activity * Component contamination * Component orientation

Good luck

Dave F

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Re: Solder Skips | 20 March, 2000

Larry, SOTs are a wonderful thing to try and wave solder! They are about as nice as Tant caps. I have found that shadowing is usually the biggest problem assuming that the other wave parameters are good, in your case it seems that they are. Couple of things that I have found to work are, increasing pad dimensions to great big old circles. IPC 782 is a good start but sometimes it does not cover wave solder requirements of SMT components they can and do need to differ, I believe that there is an addendum to 782 that covers some wave solder design guidelines that you may want to check out. Orientation may help usually have the leads parallel to the wave. Conveyor speed I have found needs to be in the 3-4 ft./min range. Crank the Omega UP! If you do all of this you will probably still have skips HaHa but they should be very minimal. ALso make sure that you are fluxing the leads and pads of these locations, they are also very prone to flux shadowing. I have had some success by thinning the flux as much as possible.

Good luck!!!


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Re: Solder Skips | 22 March, 2000


I've got extensive experience with solder skips on both 0603 and SOT23 devices. We also installed an "Omega" vibrating wave on our machine, but it didn't really have an impact on solder skips. The major difference that the omega makes is in top-side wetting and VIA hole fill.

We were able to dramatically reduce skips when we switched over to a VOC-Free flux. You can email me privately to get specific name brands. After the switch, we were able to solder even SOT23's. VOC-Free fluxes are more active because the water carrier allows the activators to ionize more quickly (vs. alcohol-based fluxes). The flux that we chose is known on the market to be more thermally stable so that there's still some remaining-even after the chip wave.

Of course, to Dave F's point, process control is everything. Your Lambda dwell time and contact seem adequate, but if you have a chip wave you should also be getting at least .5 second contact time with the chip wave. Also, most fluxes require at least 200 F top-side temp. before wave contact. You might want to double-check the requirements with your flux vendor, and adjust your profile accordingly.

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