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01005 Qualifications - Lead Free

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01005 Qualifications - Lead Free | 24 January, 2014

Hi Guys,

So I work for a small contract manufacturer which caters mainly to the defense sector. As such, our customers haven't (yet) had a great need to incorporate 01005's into their designs. Looking forward, we decided to "take the plunge" and dial in a process ahead of the requirement. So we purchased a dummy test kit (Practical Components - PC2009 AIM Solder Print Test Board and Kit). This kit has everything from 01005 resistors on up to a BGA388.

We ordered a lead-free kit (ENIG FAB finish) so as to challenge ourselves as much as possible. Using Ekra Printers, MYDATA Placement equipment and a new Vitronics XPM3i 820 Reflow Oven (eight zones, 264cm/104" of heated length, Air - Nitrogen is not an option as our infrastructure will not permit it... to say nothing of the cost). Paste is Alpha WS-820 Type 4 (ORH0).

First off, let me state that we have no problems with the printing or the placement of the 01005's (or any of the other components). Paste transfer, release and volume is excellent - 85-95% coverage of pad area at the critical 01005 pad sites (3mil foil, Fine Grain Steel with the DEK Nano-Coating). The 01005's are placing (and reflowing) on pad in perfect alignment. So printing and placement are not a problem to this point.

The reflow is the main issue I'm having with these (and only the 01005's) parts. More specifically, "Graping" of the solder joints. All of the other parts in the population from the 0201's on up to the largest BGA look great.

I've tried multiple profiling strategies using our KIC Explorer. RSS (1.25c/sec. Max Rising Slope, 67sec. soak 130c -180c, 70sec. TAL, 245c peak temp), RTS (1.15c/sec. Max Rising Slope, 62sec. TAL, 245c peak temp). preceeding profile results were averages from each profile type.) Believe it or not, the RSS profile produced marginally better looking joints on the 01005's. "Concave Graping" instead of just balling up at the termination.

I have contacted Alpha and await their response. So I wanted to ask you, what would you guys suggest for profile parameters (Max Rising Slope - Ramp Rate, Soak?, TAL, Peak Temp) when trying to develop a sucessful reflow strategy in AIR?

Thanks for any/all feedback.

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01005 Qualifications - Lead Free | 24 January, 2014

Graping is caused by a lack of flux when the oven reflows the paste.

Read [“Best Practices Reflow Profiling for Lead-Free SMT Assembly” Ed Briggs and Ronald C. Lasky, Ph.D., PE, Indium Corp]

I get nothing from any of the companies connected with this posting.

BR davef

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01005 Qualifications - Lead Free | 24 January, 2014

Thanks Dave,

I actually found that article yesterday. It is one of the better ones out there. Unfortunately, though Ed does concede that there is a "sweet spot" in the process window for trying to reflow 01005's with SAC305 using air, no further info was given.

I did hear back from Alpha this morning. They basically stated that I should try an RTS profile, 1.5c/sec. ramp, ~60sec TAL, 240c peak. Oh and everyone's using nitrogen don't you know.

Sorry, we’re located on the second floor of rented space in an old Mill building. The challenges surrounding acquiring and installing an external tank would be too cost prohibitive to warrant serious consideration. Therefore, when ordering our new oven last year we opted not to include the nitrogen atmosphere capability. Of course this reduced our costs and improved the delivery time frame.

So, I guess it's pure trial and error from here on in. I'll give it a shot. As I told my Canadian friend this morning "there's an old saying in Hockey, 100% of the shots you don't take, don't go in the net."

I'll let you guys know how I make out. Maybe it'll help somebody else.

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01005 Qualifications - Lead Free | 24 January, 2014

Yeh, I worked at Wang Computer factory in a reclaimed fabric mill with wooden floors.

One of the causes of grapping is flux loss. In their paper, Briggs and Laskey talk about flux loss due to spreading and suggest: * Graping is much less prevalent in solder mask defined pads, which confines the amount of flux spreading * Increasing the ramp rate (1-1.5°C/second) allows the flux solvent to volatize quickly, increasing the flux viscosity and lowering its ability to “run-away”.

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01005 Qualifications - Lead Free | 27 January, 2014

Dave is correct. You are running out of flux due to such a small solder deposit. Try shortening your overall time in the oven.

Less than 4 minutes to peak is where I'd start.

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01005 Qualifications - Lead Free | 13 February, 2014

Yes all above is correct, as solder deposits get smaller and mesh T4+ , actual metal to air contact surface area increases , say in contrast to T3, add to this less flux , and flux running away from the joint, re-oxidation and what flux is left, can do is stretched. These smaller larger surface solder deposit surface area, when mixed with larger ones aka the thermal delta T dilemma rears its head. So not fun all round.

Yes N2 ovens are the answer to remove this issue but at cost and not great for lower high mix makers. But even if N2 was available adds reduced surface tension and if paste , part copper balance on these small passives is not in zone tombstone issue can occur more - ie can fix soldering and get another defect.

Best to take the RTP and lowest profile length you can get, in particular the soak time prior to super heat(above liquidous) TAL time... how well this can be achieved is product Delta T thermal dependent and ovens thermal transfer capacity-efficiency in given time.

All in all open oxygen reflow with T4+ can be a difficult and narrow process window.

There are pastes that offer anti-grapping, most are no-clean types I have seen, make flux more robust- higher temp volatile solvent mixes, higher hot slump resistance etc, Water soluable less R&D has been done I suspect.

Inventec-Dehon has some anti grapping NC pastes, other brands I sure will too, but most will be NC.

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