Thermocouple Attachment Results are in!

The Rochester Institute of Technology under the guidance of Dr. S. Manian Ramkumar Ph.D. just conducted (October 2009) the most comprehensive study to date on thermocouple attachment methods.  Part I of II was to determine the most accurate and reliable method of thermocouple attachment.  Part II that has yet to be released is to determine the best attachment methods for BGAs, with the goal of seeing if there are reliable non-destructive methodologies, so stay tuned.

Results in a nutshell:

Aluminum Tape out performed all materials even Kapton! In an ideal word, the best attachment method of a thermocouple to a component is what I like to call a naked TC.  Aluminum double sided conductive tape was the closest thing to having nothing at all to attach the thermocouple.  Kapton tape is less responsive (deflecting and insulating heat), never mind if you have ever seen a saw-tooth TC plotted on a profile you know it has a very hard time staying in place on your PCB.   Additionally, High Temperature Solder which I have always considered the gold standard, is the least accurate or responsive.  When you get to the critical peak temperature of your profile, high temperature solder is sluggish to respond to the rapid change in temperatures, thus distorting your readings. As Phil Zarrow and Jim Hall discuss in Board Talk, “mass” on your thermocouple is not your friend.  Phil Zarrow:

any measurement method, the key element is to get the thermocouple in good contact with what you are trying to measure and to do it in a way that does not modify the area with a lot of extra mass or material that is going to give you an inaccurate reading….

Bingo!  This is actually what this study shows, now with the numbers to back it up.

Study Methodology:

The study looked at:

  1. Aluminum Tape
  2. Kapton Tape
  3. Chemtronics – CircuitWorks CW2400- Two Part Epoxy
  4. High Temperature Solder
  5. Loctite – 382 Instant Adhesive

The study used a KIC Explorer with standard type K thermocouples.  Multiple runs of a substrate coupon (62 mils thick plain copper coated with silver) was routed into 12 uniform 0.24″ isolated sections.

Test bank2Three identical test coupons were used and run multiple times.  KIC’s air-TC was utilized as the control to which each thermocouple was measured as the coupon traveled through all heated zones.

A total of three boards were used, running each board through twice, allowing the internal temperature of the KIC device to drop below 40 degrees C before rerunning the profile.

The tape attach methods were measured uniformly for each RTD connection, using a dial caliper, while the high temperature solder and epoxy quantities for attach were found to be visually uniform.

Mean

This graph indicates the mean temperature differential that was noticed within the oven for the various attach methods. The readings are based upon the complete profile starting at room temperature and ending at the peak temperature. The data from the cool down zone was eliminated from the analysis.

The graph shows the mean differential and the 95% confidence interval for each attach method. The Aluminum tape had the least differential (-0.48) followed by Kapton Tape, Loctite Adhesive, CW-2400 and then HT-Solder. The Confidence intervals among most of the attach methods do not overlap except Kapton and Loctite, indicating that the means of the attach methods are significant. Significant differences exist between the methods except between Kapton and Loctite as there is overlap. Clearly Aluminum tape outperforms all of the other methods.

Zone Differences

The thermocouples seem to behave similarly within each of the zones of the oven. Zone 6, where the soldering takes place or the peak temperature is reached, the thermocouple attach methods show a much higher temperature than the air temperature, indicating that the PCBs have attained much higher temperatures than the air. A closer examination of ZONE 6 reinforces the selection of Loctite or Aluminum Tape for Phase III of this project.

Conclusion:

When considering accuracy, repeatability and responsiveness, Aluminum Tape is a winner.   There are of course advantages and disadvantages to each material.  For example one can argue you can re profile a PCB set up with high temperature solder, but considering that the mass of the solder distorts your readings, this study even brings into question this bedrock of thermocouple attachment.  Never mind high temp solder destroys your PCB as well as there is little control over the size of the blog from TC to TC and board to board.   Also don’t forget every time you profile the same board again it loses some mass, which will be the focus of more blogs to come.

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Are you profiling bare boards or bricks?

No one of course reflows bare boards, so why would you profile one?  For that same matter, no one sells bricks, so why do you put one through your reflow oven?

Profiling Bare Boards:

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?

Profiling Bricks:

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:

  1. A large mass will behave differently than a production board.
  2. A large mass acts like a heat sink and will cause the oven to react differently compared to when a production board is run through the reflow oven.
  3. A large mass will result in a change to airflow due to its larger size as compared to the production board.

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.  http://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.autofocus

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.  http://profilingguru.com/category/reflow/automation/

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Why are you replacing BGAs?

There is a great post today in Circuitnet titled “BGA Replacement Limits,” that can be found under Circuitmart.  Panelists answer the following question:

How many times can a BGA component be replaced at the same location on the same PCB and retain reliability?

Mark McMeen of STI Electronics suggests that the answer may be as little as two times!

…most companies err on the cautious side and only replace twice at the same location after the initial build which is normally 2 thermal cycles for top and bottomside reflow thermal cycles.

I think a broader question needs to be asked, why are you replacing BGAs in the first place?  In my experience, often the answer is due to poor reflow profiling.  Often there is nothing wrong with the oven, PCB or BGA.   Why is it so hard to properly profile a BGA?  I believe the reason is most folks don’t have the option of placing a thermocouple underneath the BGA nor sacrificing a board in drilling a hole on the underside for TC placement.   In the old days, you could get away with snaking a TCs under the BGA, but with micro BGAs this is just not an option.  So what do people do?  They stick a TC on top of the BGA or along side it.  Many do nothing at all which is kind of scary and wind up asking question like how many times can I redo my board.

To go to show how hot of topic this is, I held a series of webinars a couple months ago with a turnout in the hundreds.  I shared some ideas, here is an abridged 8 min version of the session for those of you that missed it. Part of the answer is proper TC attachment which by the way is currently under study at RIT to see the most reliable method as well as determine if there is a non destructive methods that is both valid and repeatable.

The other part of the equation is profiling your PCB not only for your BGAs but also those components that cannot tolerate as high of temperatures. I’ve seen plenty of manufacturers so focused on a $500 BGA, ignoring pretty much what else is going on with other components on their PCB.   Certainly having the ability to define separate specifications, for example a peak temp for a DIP while addressing the special needs of your BGAs will lead to fewer BGAs having to be reworked in the first place.

After all, which is better, to treat the symthoms or the root cause?

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Four Ways to Reduce your Reflow Oven’s Power Consumption

What are you paying annually in electricity to run your reflow oven?  Not taking into account indirect costs, surcharges, taxes and added wear and tear of running your oven hotter and harder, you might be paying anywhere from $6-8K per line.   This number is based off a study conducted at Flextronics Poland, where they pay close to the US national average of $.072 kWh.

Pop Quiz: Can you rank the following in order of impact on lowering your utility bill for your reflow oven?

  • Taking Oven Control Measures
  • Peak-time Power Up Minimization
  • Off-Peak Savings
  • Profiling for Energy Savings

Well if you are savvy with your utility bill, you probably identified Peak-time Power up Surcharges as the biggest money drain.  You probably did not guess Profiling for Energy Savings as the #2 energy savings technique.

Before I take you through all four techniques, keep in mind there are dozens of variables that come into play.  The numbers I use for one municipality and/or manufacturer may be vary by location, but the point should not be lost that you can save money and not sacrifice quality production in the process.  As an added bonus many of these techniques may also prolong the life of your oven and have other hidden benefits that may impact your operation.

#1:  Peak time Power Up Minimization

The following represents a fairly typical energy ramp up of a reflow oven from a dead cold state.   Many manufacturers will use the default start up to quickly get your reflow oven up to temperature and stabilized for production.  Thanks to BTU for providing the following data.

Peak Power Up 1

Now compare this to an energy savings ramp up mode for the same oven.

Peak Power Up 2

By extending your oven warm up time by only ~15 mins, there is a 15 KW difference in the peak energy output.   Many municipalities will charge a monthly surcharge based off of whatever happen to be your peak electricity use over typically a 5-15 min period.   So if you happen to turn on all your reflow ovens at the same time, AC, coffee machine, PCs, etc., you are in for a big added surcharge on your utility bill that month.

Potential Savings:

Let’s say you are in South Carolina, Duke Energy charges $13.16  KW as a peak surcharge.  Your monthly savings would be  $198 per month.  Of course if you have more than one oven this savings will be even more significant.

Bonus:

Many smaller manufacturers that perhaps have a single reflow oven, may be close to maxing out on their service.  I’ve seen more than one case of a 100 amp facility paying anywhere from $15K – 25K to upgrade to 200 amps.  As an example, a 9 zone Heller oven will run at 100 amps at full throttle when heating up, but you can set the oven to heat up in an energy savings mode, knocking your power down to about 63 amps.  Suddenly you don’t have to go out and install more service by just making a software change.  I know that all the major oven manufacturers that sell to about 80% of the US market (BTU, Heller, Speedline, Vitronics Soltec) have this feature, so check it out.

#2:  Profiling for Energy Savings

After 5 years,  evidence is pretty conclusive that smart profiling optimization tools can reduce reflow oven energy consumption by as much as 15%.  The following three studies demonstrate where power meters were used to measure  a “before” profile to an optimized “after” profile, using KIC Navigator-Power or KIC Auto-Focus Power.

There are basically three steps that should not take more than 15 mins to complete:

Step 1: Audit your SMT line speed.  You want to determine where is your bottleneck.  It is not uncommon to find the reflow oven running faster by 20% or more to the slowest system on your line such as the pick and place or screen printer.

Audit

John VanMeter of DG Marketing timing the line

Step 2: Run a profile

Profile

KIC Explorer 7 CH

Step 3: Run KIC’s power optimization feature in KIC Navigator.   As an process engineer I would set up your minimum allowable conveyor speed in the software above your bottleneck speed.   For example, if your current line speed is 30 in/min and an audit reveals your screen printer is running at 20 in/min, set your tolerance in the software to 23 inches.  You don’t need to make your reflow oven a possible bottleneck!   Lastly, you have the freedom to set the maximum allowable process window index (PWI).  In other words, if you know your oven can handle using up to 70% of your available spec, without any drift/variability causing you to go at times out of spec, you know your limit.   It really depends on the personality of your reflow oven.

Optimization

Potential Savings:

Based off the Flextronics Poland study cited above which was conducted on a Heller 1912 EXL  manufactured in 2005 and using a kWh rate of $.076 which is practically dead on to the US national average, results in $1062 in annual savings.  Which depending on the state of manufacturing can be as high as $2472 annually per oven.   15% savings which was the case at Flex Poland, is not unusual as you will see similar results in the Delta study in Arkansas to be released in October’s issue of  Global SMT.

Bonus:

Added features to having KIC’s optimization software Navigator-Power or Auto-Focus-Power are the additional tools you now have for decreasing defects.   It is hard for me to know what it costs you each time you send a PCB to rework, the cost of time spent profiling when you should be making on-time deliveries and the stress and aggravation of trying to produce a run of a 100 boards when your customer wants all 100 back!  Auto-Focus power allows you to make a very good first guess profile of new board before you even profile!  You can find discussions on these tools throughout this blog.

#3:  Off-Peak

Off-peak hours vary widely per locale.   Also depending on the time of year it can vary.   Nevertheless, if it is possible to run even a portion of reflow production in off-peak hours your costs kWh can sometimes be half of on-peak prices.   I like to use the same rate chart example give above for S. Carolina where Duke Energy charges between 2pm – 6 am, $.0297 kWh vs. $.0563 kWh.  Many of us logistically may not have in place a night shift, but most of us can certaintly take advantage of production after 2pm.   This is more an issue of smart planning, an exercise in management.

Potential Savings:

If you can schedule a quarter of your production off-peak, and by doing so are able to reduce your rate per kWh by half  which is possible in some municipalities your savings could be on the order of $62-74 per month per reflow oven.  I came up with this number by again using the Flextronics study as a guide, where they are paying a kWh rate similar to the US national average and shelling out between $5.8K – 7K per year per reflow oven.

#4:  Oven Control Measures

By buddy Bob Powledge of DG Marketing out of San Antonio, Texas likes to say, “sure the heck cheaper to blow air than to heat it up!”  I agree and there are studies to prove it.   Basic physics comes into play.  It you can move more heated air over a surface, it will heat up more efficiently and faster.   This is why squirrel cages have by and large gotten bigger over the years and other technologies such as static pressure have come about.   In one study conducted by BTU who plays around with the idea of static pressure another approach at improving heat transfer rates, the same set-points could increase temperatures by as much as 5C  by only changing static pressure.   Take this to the next step in our discussion, you can thus REDUCE your oven set-points by that same amount thus reducing electricity usage.  Just a word of caution.  If you use blowers, you don’t want to crank them up too much unless you like moving components across your PCBs.  Many ovens have precision controls for this reason while others offer this as an add on option.

Static Pressure

Potential Savings:

I have to take a wild guess in what this translates into dollars since there has not been a study specifically addressing what this means in terms of electricity savings.  Considering we have so far been able to build cost models from the profiling studies we can extrapolate some reasonable numbers.   In the Delta study, the cumulative setpoint change across their 8 zone Vitronics Soltec oven was 198 C.  If you run through each zone, some zones like Z1 there was no change, but when you get to Z5 the delta was 50C!  So how do you compare both?  If you achieve a 5C reduction across 8 zones or cummulatively 40C and you compare this to our 198C study, this would represent 20% difference.  So take our numbers from our profiling study and cut them down to 20%.  Remember in the national average example, you could expect $88 in mountly savings per reflow oven, therefore for this example we might see about 20% of that number or $17 per month per reflow oven.   I please welcome any oven manufacturer to share the results of a study that questions these assumptions since some guesswork is involved.

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Thermocouple Attachment Discussion

Phil Zarrow and Jim Hall of ITM Consulting have a very good piece on TC attachment on Board Talk hosted by Circuitmart.com.

In their first session, they talk about permanent TC attachment, such as high temp solder and epoxy (click here for a link to their recording).  Yours truly left a comment with the boys:

We are a big fan of conductive Aluminum tape, used along with Kapton for strain relief like you mention in your podcast. We talk about high temp solder and epoxy which can work also, but like you said you got to be careful of mass. Lot of times we see unequal amounts applied per TC that can throw your readings. What is your take on aluminum tape, realizing of course it is a non permanent solution?

Well, they came back with a terrific response (click here for a link to their recording), where they make a clear distinction between destructive vs. non destructive methods.  Non destructive methods are often the only option, since customers cannot sacrifice a board for profiling.

Phil goes on to say:

any measurement method, the key element is to get the thermocouple in good contact with what you are trying to measure and to do it in a way that does not modify the area with a lot of extra mass or material that is going to give you an inaccurate reading….

Phil talks about using for example Kapton as a strain relief to ensure there are no stresses on the point of TC attachment.  I’ve been saying for years to use techniques such as window paning where you apply Kapton around the boarder of your aluminum tape to help keep your TC secure if profiling more than once the same PCB.  Make sure not to put Kapton over the bead since Kapton can behave as an insulator.

I think Phil makes a great point on emphasizing the “size” of the tape you are using.  Again you don’t want the material’s mass to become an issue.  So the name of the game is don’t go overboard.  Personally I prefer a 1/4″ square piece of aluminum tape along with 1/4″ Kapton.

Jim Hall makes also an excellent point that the same goes for “destructive” methods when using high temp solder and epoxy.  You don’t want to overdo it, or the mass can effect your readings.   I would add further that you need to be very careful that the mass be equal from TC to TC.   It has been my long held belief that the blob of epoxy or solder if of unequal amounts TC to TC, PCB set up to PCB set up will add variability into your process.  Just keep your materials to a minimum to get the job done.

Many of these assertions are currently under review by an RIT study.  Hope to have results as early as the end of this month.  KIC conducted a study 10 years ago on all the materials mentioned (click here for the report).  Since a decade has past, one could assume materials have improved therefore warranting a second look.  Stay tuned!

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Running lead free and eutectic PCBs simultaneously on the same reflow oven

Surface Mount Technology ran a piece titled Parallel Processes: Simultaneous Lead and Lead-free Soldering with a Single Reflow System written by Hans Bell of Rehm Thermal Systems GmbH.  Hans details a study where by controlling conveyor speed of each lane of a dual-lane system, it is possible to run both a lead and lead free product simultaneously.

The devil of course is always in the details:

Definition of the process window must always be based on the “weakest link,” namely the component with least amount of thermal stability during the soldering process. If two different processes are to be set up next to each other in the same reflow system, and if thermally sensitive components are included on the PCB, great flexibility is required for parameters configuration.

The ability to develop process windows for each product leaving enough room for each to call upon the same oven zone set points is key and of course taking into account special temperature tolerant components on each board.  Hans’ idea is intriguing.  Based on my experience in a world were many PCBs manufacturers struggle to profile or perhaps do not profile at all,  this is certainly a tall order.  Nevertheless his idea is do’able for perhaps many processes, since changing just the conveyor speed to reduce product changeover on a single lane oven is being done today (click here for an excellent application note using KIC product’s to achieve this end).  Why this couldn’t be adopted to a dual lane system running both lead and lead free simultaneously has its merits.

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No Waste: Beyond PCBs in Reflow Profiling

Article is from SMT Magazine

In many situations, EMS providers cannot waste a PCB for thermal profiling. Some ovens are equipped with profiling tools to generate an accurate reflow recipe without thermal profiling. This saves time, labor, money, and materials, but there are limitations.

By Brian O’Leary, KIC

There is a right way and a wrong way to set up a reflow oven to manufacture a new PCB assembly. This article suggests using the wrong method, but for the right reason. If an electronics manufacturer is prevented from following the correct method for setting up the reflow oven for a new production run, does a fallback position exist where they can still expect good results? For example, contract manufacturers find themselves in a not-so-uncommon situation where the manufacturer receives 100 boards and is expected to give a 100 assembled boards back. Sacrificing a single PCB to the profiling process is not an option. In another example, a manufacturer has PCBs that run in the several thousands of dollars. A suitable scrap board is not available for profiling, due to the cost incurred for the lost PCB.

Advantages and Disadvantages of Traditional Reflow Oven Set-up

The traditional method for setting up a reflow oven to manufacture a new PCB assembly is to attach thermocouples (TCs) to the PCB and run a series of profiles. Multiple profiles are usually required for the technician to adjust the oven recipe until an in-spec or deep in-spec profile is found. The introduction of lead-free assemblies has made this task more difficult and time-consuming. However, automatic prediction software and process optimization software have significantly cut down on the number of profile iterations required to determine the oven recipe that provides an in-spec process.

The benefit of this conventional reflow profiling method is clear: It achieves a deep in-spec and therefore stable process that is fundamental to good end-product quality. It also provides documentation to the client that proper process development work was performed.

These procedures, however, tend to sacrifice one or more PCBs. One reason for this concerns the TC attachment method. There are several TC attachment solutions, some more destructive to the PCB assembly than others. The use of high-temperature solder wire is a reliable method, but tends to damage the PCB assembly. Aluminum tape is also a reliable and repeatable method with the added benefit that the tape can be removed after the profile without damaging components.

year_Par_30864_Image_400_240_1

A second cause of PCB damage is the fact that each subsequent thermal cycle through the reflow oven raises the risk of latent or real defects as solder joints are re-reflowed, components are exposed to multiple reflow cycles, and the properties of the substrate changing. The PCB gets lighter, discolored, and more brittle with multiple profiles. Therefore, even with non-destructive TC attachment methods, such as aluminum tape, the PCB may need to be discarded when several profiles are run.

A final risk is that the technician selects, often guessing, a wrong initial oven recipe prior to the first profile. The initial recipe could damage the PCB. This could happen when the peak temperature is too high, the slope too steep, the soak prematurely dries out the volatiles in the paste, etc.

Profiling the Reflow Oven, Not the PCB

Modern reflow ovens are a far cry from their legacy siblings. Each oven model produced in volume tends to have very tight and similar thermal characteristics to each other. Equally important, these properties do not change over time as rapidly as in the past due to better flux management, improved oven control systems, more precise mechanics, etc. This enables new thermal process tools that “learn” the behavior of each oven model. To capture the thermal properties of a specific oven model, numerous profiles are run on a variety of PCB assemblies under differing process windows. This database will cover all but the most unusual applications encountered in SMT production. Once this work has been done, it is a simple matter of copying the information onto all the similar oven models. At that point, the operator could simply enter the basic information of the application, such as the length, width, and weight of the PCB assembly as well as the appropriate process window, and the oven will find its suitable recipe (zone temperatures and conveyor speed). This recipe will yield an in-spec profile in the vast majority of the cases without the need to run a profile or attach TCs. Experience with such technologies also suggests that when the recipe generated by the new thermal process tools does not yield an in-spec profile, it is usually very close.

Some U.S. oven manufacturers have completed this work. These reflow oven makers ship ovens with a fully functional database that essentially allows their customers to set up for new production runs without the need for profiling and sacrificing PCBs.

These systems do have limitations. The first was alluded to above, namely that there will be a small percentage of the applications that will not be processed in-spec. The fail-safe method is to wait for the oven to stabilize on the suggested recipe and then run an old-fashioned profile to verify whether it is in-spec. If out of spec, it should, in the vast majority of the cases, be close enough to achieve an in-spec profile on the second try. One profiling pass through the reflow oven, with aluminum tape used for TC attach, should not damage the PCB assembly.

year_Par_87154_Image_500_579_1

Another limitation is that an oven will, given enough time, eventually change its thermal properties. Wear and tear, changes in exhaust conditions, preventive maintenance, and a host of other factors will have an accumulative effect on the behavior of the reflow oven. Therefore, the initial database will need to be updated. This can be achieved by running some real-life profiles from time to time, and feeding this fresh information back into the database.

The final limitation is the fact that a system that eliminates profiling, by definition, does not have a profile recorded for the specific assembly. This means that there is no documentation or evidence that the PCB was indeed processed in-spec. Some customers will accept this, while others will not and require reflow profile documentation.

Conclusion

The correct method for reflow oven set up with a new application is to profile the PCB and dial the processed deep in-spec using prediction software. If the electronics manufacturer either cannot or will not perform this task, there are now thermal process tools available that achieve a more than 80% effective solution. Oven-inherent programming produces an in-spec recipe in the vast majority of the situations with no need to profile or sacrifice a circuit board. This technology also saves set up time and associated labor.

Using a profiling technology without an actual PCB profile run is also far better than doing nothing. Many manufacturers in our industry currently do not profile at all, or they limit their profiling to a single application a few times a year. If you do not want to do traditional profiling at all, oven-generated recipes can be an intermediary, rather than blindly reflowing.

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Non Destructive BGA Profiling Test #1

I am currently investigating a non destructive method of BGA profiling that is reliable.  Here are the results of my first test.

Set Up:

Four thermocouples are attached to the same BGA (TOP, SIDE, INSIDE and BOTTOM surface), as pictured below.  Conductive aluminium double sided tape is used along with Kapton.  A KIC Explorer is the profiler.

To see more on Thermocouple attachment visit my post:  http://profilingguru.com/tcs/thermocouple-attachment/

A hole was drilled out to attach the INSIDE TC.

pic1

pic2

Results:

Two tests were run, the first was running the board on the belt followed by running the same board on the chain/tab conveyor.

sample1

As you can see the delta for ramp and peak is the greatest, while soak is minimal.  The inside TC runs the hottest and the underside bottom TC follows fairly closely the behavior of the inside TC.

sample2

This second profile was run on the belt with the same board but for a different BGA.   Again we see similar behavior, where the INSIDE and BOTTOM TCs exhibit similar behavior.

sample3

This third profile was running the same board and same BGA as in the second example but this time on the chain/tab.   Interestingly, all TCs were a good predictor of the INSIDE TC except when getting to the cooling zone.  The BOTTOM TC was only a good predictor of the INSIDE TC.

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Plugging the Hole in the SMT Reflow Inspection Process

MB (Marybeth) Allen, General Manager of KIC Europe in an interview with Globalsmt.net makes a terrific case for RPI (Reflow Process Inspection). MB_Allen

Here are some excerpts:

Q. 2009 saw the introduction of your RPI In-Line Process Inspection System for SMT reflow ovens.  For manufacturers currently relying on AOI and X-Ray systems to carry out inspection functions, can you explain how this system works and why RPI should be the choice for this process?

Automated inspection systems have become critical in controlling quality throughout the manufacturing process.  SPI (solder paste inspection) and AOI (automated optical inspection) are excellent defect detection tools, within the limitations of their design.  The RPI (reflow process inspection) inspects the reflow process for each and every manufactured PCB.

The quality of a solder joint is not only a function of whether there was adequate solder, accuracy of placement, missing components etc., but that the solder was processed correctly.  For example, the peak temperature needs to be high enough, but not too high to damage the component; the time above liquidous must be within the required range etc.  The AOI machine is not designed to check for these critical events.

KIC’s RPI verifies that the PCBs have been manufactured within the required thermal process window.  Perhaps the best example of where RPI complements AOI is in the soldering of BGAs and other Area Array Packages, where the AOI machine cannot see the solder joints as they are hidden from view by the component body.  RPI even complements X-Ray machines as these inspection systems cannot tell whether the solder joints were processed in accordance with the required profile specs.

Q. So KIC RPI offers both oven and product data in one solution, this obviously enables the operator to harness this key data and use the yield charts to refine the process. What type of data do they receive and how easy is this to understand?

RPI automatically generates both Yield and DPMO (Defects Per Million Opportunities) production charts.  There’s really nothing for the customer to do as the information on all boards produced is captured automatically.  You’ve seen these charts in many factories showing product data for many steps in the manufacturing process.  However, previously data from the reflow process was missing.  Only reflow oven machine data was available.  KIC’s RPI now provides this missing key product process data, providing another key link to product quality.

Q. This product offers a timely solution for manufacturers in this tough climate and I understand it has already received awards for its innovation. What has been your feedback so far?

Yes, RPI has already received several awards around the world.    People are looking for a solution to save money and ensure continued quality control.  When I visit customers and prospective customers their initial questions or requests can be taken care of by using RPI.  It’s wonderful to be able to say “Yes, RPI can help you with that” to most of their requests.  We have plugged the hole in the inspection process.

For the full interview go to: http://www.globalsmt.net/content/view/7583/70/

Awards:

2009 EMAsia Innovation Award in the category of Process Control Software for its RPI in-line inspection system.

2009 NPI Award in the category of Process Control Tools for its RPI in-line inspection system.

Innovative Technology Center Award at Apex 2009

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BGA Profiling Webinar Recording

The following presentation was first held as a 30 min BGA Profiling webinar in July 2009, with over 120 participants.  Due to its popularity an abridged 8 min version was created.

To subscribe to my Podcast for iTunes (click here).

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