So, our reflow profile does match the solder paste specification. The cooling ramp rate, from Figure 2, is (250-90)☌/(5.7-3.8) min = 160☌/(114 sec) = 1. 40☌/sec, which is within the acceptable rate of the solder paste spec. The peak temperature is 250☌, again within the specification recommended range as seen in Figure 1. There is no “soak” in this profile, so we can ignore this part of the solder paste spec.įrom Figure 2, the time above liquidus is 4.4 – 3.1 minutes (78 Seconds), right within the recommended range of the solder paste spec. This result is just over the recommended spec, but within the acceptable spec as seen in Figure 1. Ramp Profile: From Figure 2, the oven goes from room temperature to liquidus in 3.1 minutes (186 seconds) this gives a slope of (219 – 25)☌/(186 - 0 ) sec = 194/186 = 1.04 ☌/sec. Now, let’s take each reflow profile requirement individually: The solder paste reflow specification is shown in Figure 1 below.įurthermore, let’s assume that we have a reflow profile that we have used in the past, as seen in Figure 2. Assume we want to start using Indium Corporation’s Indium8.9HF Pb-Free Solder paste. Matching a reflow profile to a solder paste spec is a required skill for an SMT process engineer. SiP & Heterogeneous Integration & Assembly (HIA).The Indium Corporation & Macartney Family Foundation.Note that in the graph above the "ramp rate" is actually measured as 0.75☌/s and is from ambient to peak temperature (not 1. The reflow process window is becoming very narrow and this attribute (ramp rate) has become as important as time above liquidus and peak temperature. This rate becomes even more important as the solder paste deposit continually decreases in size - as we move to 0201’s and smaller and from 0.5mm pitch BGA’s. Due to this miniaturization, the emergence of a defect known as " graping" has also become fairly well known. This gently evaporates volatiles and helps minimize solder defects such as solder balling, solder beading, and tombstoning. Please consult AIM Technical Support for targeted process and profiling assistance. Soldering defects can be caused by a myriad of other process/material variables. This defect information is specific to potential causes that are reflow profile related. And is more practically used in a ramp-to-spike type profileįrom the view point of the solder paste, a low ramp rate is desired, usually 1-2☌/s. Flux/solder paste spatter Malleable/ weak solder joint Poor or non-wetting Popcorning/. Included in the Product Data Sheet, among other things, are parameters which guide the customer in designing an SMT reflow profile. Exactly HOW that is done is critical to your success. The ramp rate may be better described as the rate (change in temperature over time) from ambient (room temperature) to peak. Solder paste is made to be reflowed in the SMT process. The focus of max slope is more from a component view point, to avoid thermal shock, usually 3☌/s is recommended as the upper limit The change in temperature between ambient and the first zone then is a minimum of 75☌ (assuming 25☌ as ambient) and so it’s easy to see that the greatest change in temperature (max slope) in most cases is typically found in the first zone The max slope is very often attained in the first zone as the PCB moves from ambient temperature into the oven. In most cases the oven zone setting for the first zone is 100☌ or better. The reason for addressing this subject is that, often, there has been some confusion in regard to the difference between max slope (a category reported on most profiling software) and the ramp rate listed on a data sheet. The data sheet gives general recommendations, for time above liquidus, peak temperature, and ramp rate. The resulting surface oxide can lead to a number of solder defects such as voiding, beading/balling, graping, and head-in-pillow. that challenges the solder paste’s flux to effectively perform its fluxing action. Solder paste is made to be reflowed in the SMT process. Figure 2 - Ramp/soak/spike reflow profile. Below each thermocouples results are shown as they relate to each of their designated process windows (Figure 8). SiP & Heterogeneous Integration & Assembly (HIA) Having the ability to build a reflow profile around the entire populated PCB is critical to achieving the solder paste recommendations, maintaining the component specifications and reducing voiding.The Indium Corporation & Macartney Family Foundation The standard reflow profile has four zones: preheat, soak, reflow and cooling.
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