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Wave Soldering No-Clean Bottom-Side SMT

Chris McDonald


Wave Soldering No-Clean Bottom-Side SMT | 28 April, 2000

We have had nsome new products come in that require Bottom side wave soldering (SMT). I have SOIC's 1206, 0805 that are Glued then Wave soldered. I have had trouble with bridging and no-clean residue with these pcbs. I have a Econopak 2 SMT two zone with Chipwave(Turbulent) and Lamda Wave. I use the Lamda and Turbulent when running bottom smt. How do I profile with the Turbulent wave should I burn off all of the Flux before the Turbulent or before the Lamda? I have played around with different profiles and I have no luck with this. Chris

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Re: Wave Soldering No-Clean Bottom-Side SMT | 2 May, 2000

There are a number of different things to ask youreself here. What type of flux are you using. 330, 351, 310 etc. Do you have a hot air knife? As for the residue, that's gonna show on almost any wave soldered pcb. We have fought the issue for a long time and found that a vox free flux such as the nr330 works best. How are you profiling your wave? You may wanna try turning your pcb's 90 degrees and seeif it helps also. You don't wanna burn your flux too fast as it will cause skips down the line also due to the fact that you're allowing enough time to let the flux do its job.

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Re: Wave Soldering No-Clean Bottom-Side SMT | 2 May, 2000

Donnie is correct. "NO-Clean" doesn't translate to "no-residue!"..... who's giving you hassle about this - your ICT guys??!!

Residue remaining on your PCB substrate is a function of many different things - flux deposition, solder mask (glossy means more residue!), thermal profile, and wave contact time. You need to compare your flux vendor's data sheet with your thermal profile - make sure you're getting adequate top-side temperatures to both activate and burn off the flux, and also make sure that you're spending enough time in the wave (you can use a glass plate, or a fancy tool like ECD's WaveRIDER to check this).

If you have SOIC's on the bottom-side (very bad design practice), it's almost imperative that you have a hot-air knife, OR try getting a 45 degree pallet. I've heard that this works in terms of helping with bridges.

Donnie is correct in the fact that you need to research a flux that is thermally stable enough to survive the chip wave. If you're flux isn't thermally stable, then most of your activators will have burned off in your chip wave...Some of the newer fluxes out there have such properties. Also, with fluxes like Alpha's NR330, you can get by with minimal deposition (typically 800 to 1000 micrograms per square inch - whereas most fluxes require 1000 to 1500 ug / in2) and still get nice solder joints and top-side wetting. I just finished a flux evaluation for my company.

My paper on VOC-Free flux is supposed to be posted on SMTNet library, but technical difficulties were encountered. Hopefully, a kind person from SMTNet's staff will be able to help me out...

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