2009 Presentation at SMTAI San Diego on how to increase reflow oven throughput without sacrificing quality profiles in the process. After you watch this 3 min video you will learn an easy method of increasing throughput on your reflow oven for a particular profile in 20 mins or less.
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2009 Presentation at SMTAI San Diego on how and why you need to drive your reflow profile deep within specification. After you watch this 8 min video you will never take profiling for granted again!
To view the complete video series (click here).
To subscribe to my Podcast for iTunes (click here).
Podcast: Play in new window | Download (Duration: 8:10 — 39.9MB)
What’s wrong with this picture?
Well if you have ever used Kapton tape to attach a thermocouple, you have certainly seen your share of profiles like this!
So what, it is a perfectly good profile, right? Yes, but no. I had a customer who was using KIC’s Navigation (auto prediction) to help create a better “deep in-spec” profile. The only problem, they were trying to optimize on a TC reading that was bouncing literally all over their PCB. Navigator is an awesome tool, but it can only work with what you feed it. If you feed it garbage, it will give you garbage. In their case, it was trying to find them a new solution where literally every time the board was run the bouncing TC that was attached (or I should say was not very well attached) with Kapton was giving false readings. Navigator would give a different solution based on what the TC was reading at that given time. It is like try to put post-it notes on the ocean.
Solution is very simple, eliminate the TC reading from your graph. You can easily do this with the profile you just ran. Look what happens, you go from a far out-of-spec of 126% PWI to a far in-spec of 48% PWI.
So you saved your hard work this time, but you are after all one thermocouple reading short. You added that TC to your profile for a reason. Next go around, do yourself a favor and use a better material for attachment, such a conductive double side aluminum tape, which by the way, a recent study from RIT proves it a superior attachment method aside from sticking to your PCB much better.
I am often asked the question about how to handle components that are close to the outer edge of a PCB. Today a question came in on Circuitnet to highlight this problem:
Title: Issues with BGA Components Near PCB Edges
What issues are we likely to see when we place BGA components very close to PCB edges?
What impact might it have on reliability?
Will equipment (screening, placement, reflow, etc.) require modification?
T. B.
I leave it to the screen printer, pick and place and reflow oven guys to answer the equipment part of the equation, but I can answer how one can determine with a profile if your BGA is getting what it needs as well as how other aspects of your PCB are impacted.
There can be anywhere from a 2 – 5+C variation in temperature across the belt. For example, BTU uses this homemade fixture to test for uniformity. The idea is fairly simple. With a set of type K calibrated thermocouples, you can easily monitor 6 TCs across the belt. You want obviously to see the least amount of variation (if you were wondering the front TC is for measuring air temperature which is also used for automatic mapping of the profile to the oven zones with KIC2000 software).
BGAs typically require more heat to reach their peak temperatures than smaller massed components like electrolytic capacitors. For example, your BGA might have a peak temperature of 245C.
While your electrolytic capacitors cannot tolerate as high as a peak temperature, therefore you want to set their maximum peak temperature lower, for example to 235C (this is just a relative example).
With KIC2000 software, you can define each component in isolation. If the BGA is off on the edge, I might need to bump up even further my peak temperature spec since in many reflow ovens, the outer edge near the rail is the coolest. This is why you see some ovens with heat tape running along the rails! Keep in mind of course as you crank up your oven to reach higher temps to reflow your outer edge BGAs, everything else on your board is also going to be impacted. More the reason you better be hooking up thermocouples to temperature sensitive components to ensure they do not get fried while you are focusing your attention on your BGAs. Profiling software that can “balance” the board is a must. If there ever was a case where software can help solve complex problems in profiling, here you go!
I had a webinar back in July talking about BGA profiling. There is also a video that illustrates what I explained above. You can find this in an earlier posting: https://profilingguru.com/reflow/profiling-bga-webinar/
Today I came across CM doing exactly this. They were processing networking boards. They were just too complex and expensive to profile, so the solution instead of finding a scrap board or some other reasonable substitute was to profile it as a bare board. I guess the thinking was it is better than nothing, but can anyone honestly say that a bare board comes close to representing a true production board? After all wouldn’t you agree profiling modern boards with mixed components, higher densities and micro-BGAs are already a challenge and to think profiling a bare board would yield any reliable results is a stretch?
So if this is such a terrible solution, what about putting a brick through your reflow oven? A brick, come on Brian, who does this? Well what do you think you are doing when you take one of the many fixtures available on the market that are used for characterizing an oven and using it to profile? I bet if you melted them down (with profiler included) they aren’t far off in mass from a brick. Consider the following attributes of a large mass:
Now notice I included the profiler as part of the mass. Many fixtures further add mass by adding a two pound weight to the fixture! Now don’t get me wrong, these fixture do give you a relative measurement from week to week or month to month as to changes in the oven, but they do not tell you if your product is in spec nor provide a thermal profile. Changes in the oven do not neatly correlate to changes in one’s profile. After all how can they? Chaos theory came out of the field of thermal dynamics, nothing neat about it. Just like a bare board is no substitute to a populated PCB, a brick is also no substitute.
Don’t take my word for it, hear it from the oven manufacturers themselves. https://profilingguru.com/reflow/standard-calibration-tool-for-reflow-process/
Here is a quote from Fred Dimock of BTU:
Oven manufacturers normally use custom designed test fixtures to simulate a board but their real purpose is to measure uniformity across the oven and confirm that the oven is working correctly.
….I have personally seen companies place unrealistic performance specifications on reflow oven testing with (fixtures) boards that have little to do with actual production needs. For example, we once were required to show that an oven could reproduce an inspect ramp soak spike profile on two 12 X 18 inch aluminum sheets that were 0.040 and 0.080 inches thick without changing any recipe parameters….
….From a surface mount manufacturing point of view – single board oven performance testing has little benefit. The real answers are to use actual boards with TCs placed on the critical components….
Both solutions profiling bare boards and bricks are inadequate. Make matters worse if you do both such as I saw with this CM, the results are only compounded. In other words, you are developing a profile based on an unpopulated board and afterwords taking measurements with a thermal mass that does not in anyway represent how your oven will in fact react to a production board. This is classic garbage in, garbage out.
Now there are alternative solutions that don’t require the destruction of a production board in the process. Many of the automated systems will create accurate virtual representations of production boards without the need to attach a single thermocouple. There are also some brilliant software solutions that allow you to create accurate profiles without the need to run a profile. https://profilingguru.com/category/reflow/automation/