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How to PROPERLY interpet a supplier's paste profile documentation & specification?

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stu

#71522

How to PROPERLY interpet a supplier's paste profile documentation & specification? | 23 December, 2013

I'm fairly new to SMT, but highly experienced in other materials engineering areas. But have found the definitions/specifications for pastes to be both confusing and inadequate. I have often see graphical representations of the "desired" thermal profiles which typically show 3 profiles. I have attached an example of a Shenmao paste where the documentation displays one profile referenced as RTS, a second profile referenced as RSS and a third profile which is not labeled. I then see specifications displayed on the chart which cross over between the two profiles. Specifically, the pre-heat specification which graphically is shown as the range from the RSS (@ 155 C) to the third unlabeled profile (@ 185C). I get the impression that the supplier is indicating to treat the paste as a combination of these profiles where they create a band of allowable response, particular as the specification below the chart references that temperature range explicitly. This seems completely unscientific and unappealing to me. I also see an initial ramp specification which appear to be defined across fixed temperature values and inline with the RSS profile (not the band) as shown in the pictoral representation, though I have see references to moving averages over some particular time frame or oven distance from other sources. It would seem to me if that I were targeting only RSS, then this pictoral indication of the intial ramp would be valid, but in that case, the corresponding RSS profile would be at the center of some otherwise imagined band (not an extreme upper limit as would occur if I were to combine these three profiles into a single band). One implication would be that my peak temp target would be exactly 250 and that I would have a further range around this peak target which is not defined. I would be interested in reading some DETAILED discussion on the mechanistic underpinnings of these specifications, the subtleties of specification interpretation and how to best implement to be robust when consider a range of panels and panel attributes.

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#71523

How to PROPERLY interpet a supplier's paste profile documentation & specification? | 24 December, 2013

Hi,

it is a not given clear here. I will tell you some basics about the profiling:

1. Profile stages A. Preheat - the board preheats from room temp to 130-150C depending on the paste B. Soak - 150-170(or other range depending on the paste). here the flux is wetting the pads and basically prepares the paste for soldering C. Reflow - over 183(Leaded paste) and over 217(for most common leadfree pastes) in this zone the the paste becomes liquidus D. Cooling - the pastes hardens in a solder joint

2. There are mainly two types of profiles for the paste:

A. Linear - temperature is increased in a linear function to the time up to reflow zone B. SOAK - goes linear in the beginning(preheat), than the slope becomes much smaller(Soak)and then goes to reflow(reflow)

in the industry they call the Ramp to Spike and Ramp Soak Spike(I think) and that's probably what RSS and RTS stand for. Choosing the right one depends on the assembly you have. Each of them helps you to reduce some defects but generates others....For this you should go deeper and read more, but the rest should give you the basic idea.

Regards, Emil

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#71524

How to PROPERLY interpet a supplier's paste profile documentation & specification? | 24 December, 2013

I wouldn't get too tightly wrapped around the axial of paste suppliers recommendations of thermal recipes. Said another way, "Do not count on the solder paste representatives for good technical advice--they are the ones who came up with these "'TIME ABOVE 183" or "TIME ABOVE LIQUIDUS" concepts, which are technically woefully inadequate." [W Engelmaier]

Your supplier says: * ramp up rate(30~150 ?) : 1.0~2.0 ?/sec * pre-heating time(155~185 ?) : 30~120 sec * time period above 220 ? : 30~100 sec * ramp up rate during reflow: 1.0~2.0 ?/sec * peak temperature: 230~250 ? * ramp down rate during cooling: 1.0~6.0 ?/sec

... That's a fairly broad range [for each of those characteristics] Your board design and the components on the board are other factors that you need to consider in selecting the characteristic of your thermal recipe.

The most coherent discussion of thermal profiling is here: IPC-7530 Guidelines for Temperature Pro?ling for Mass Soldering Processes (Re?ow & Wave) [ipc.org/TOC/IPC-7530.pdf?]

Each of the major thermal profiler device suppliers offer excellent discussion of their approach to developing recipes on their sites. Profiler suppliers that come to mind are: * kicthermal.com * ecd.com * datapaq.com * circuitmaster.co.uk/profiler.html

Here are some papers that may help: * car-san.com/specials_pdfs/doc_20090427144226.pdf * ems007.com/pages/zone.cgi?a=60702 * conceptronic.com/products/solder-reflow-technology-handbook/section3.pdf * axiomsmt.com/articles/global8.4us.pdf

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