Tips on Cooking Both a Perfect Thanksgiving Turkey and a PCB

Why does it take half a day to cook a Thanksgiving turkey?  The answer is simple ― you have 20 lb of bird that simply cannot just be nuked in a microwave like last night’s dinner.  If not properly thawed, prepared and monitored, you either have an overcooked, dried-out bird or worse: Salmonella. Strangely enough, as you will see in a moment, PCBs are not that much different.

Let’s say you skip the thawing process and in your haste stick a frozen bird in the oven.  What happens?  The bird may look properly cooked on the outside, but as soon as you try your skill with the carving knife, you either hit bedrock or the inside is completely raw. OK, I will admit I speak from personal experience on this one (please do not bring this up with my wife).  Are PCBs any different?  Well, your reflow profile has a preheat phase, with the purpose of bringing your PCB to temperature. In other words, the entire mass of the board with all its components is gradually brought to equilibrium. If you do not do this, you run the risk of thermally shocking your components when they hit reflow and peak.  Thawing your bird and preheating your PCB ― you have the same objective in mind.

So, for the vast majority of us, we really have no idea when the turkey is fully cooked until getting an internal reading. A PCB is no different. On the surface, both might look great, but upon closer inspection, you discover some components have defects due to improper reflow or, for that matter, when you cut into a turkey that is still pink it really hits home that you aren’t cooking a TV dinner.

turkey-in-Spec_SM01

Because of this, as we all know, a 20 lb turkey requires a thermometer. I will concede that some of you use the old “poke the bird and check for pink until done” trick. Let’s assume you are not as skilled, like me, for example. Would you seriously cook a turkey by relying solely on the oven’s temperature reading on your stovetop?  Of course not, but why do some of you profile your PCB by relying on your reflow oven’s reported readings? Are either situation that much different?  Actually, yes. Your nice self-contained turkey cooking oven is more of a steady state, but there remains a large difference between what is reported by the oven and the internal temperature of your turkey. In contrast, your PCB is exposed to anything but a steady state environment because it rides on a conveyor through different heated zones with blowers, extraction systems and both ends of the oven even open to the elements!  For this reason, any oven manufacturer will adamantly tell you to profile and with regularity. Alright, you may have learned how to cook a turkey in your Mama’s kitchen and, in fact, be skilled at not using a thermometer; however, I doubt any serious SMT manufacturer would take a similar approach, checking your PCBs regularly for “doneness” in your reflow process.

What about placing the fate of your Thanksgiving feast on the cheap-o plastic pop-up indicator that likely came with the turkey? Do not laugh. How many of us use the trailing wires that came with the reflow oven?  Now to be fair, both work in principal; otherwise, you would have the likes of Purdue Farms with food poisoning lawsuits on their hands, but they only give you ballpark readings in many cases. By design, the turkey is going to be a little overdone and dried out.  Your PCB, on the other hand, cannot afford to be a little overdone or it is simply OUT of spec.  You can get by with eating the overcooked turkey … the gravy and mashed potatoes are there to make up for less than a perfectly cooked bird. But your PCB will not be as forgiving.  Trailing wires, never mind being cumbersome to use, have a tendency to kink and stretch, which compromise their readings.  They also are susceptible to 50 or 60 cycle noise from some reflow oven environments, further questioning their accuracy in some cases.

So you want to cook the perfect bird. Who doesn’t? So you pony up for a stainless steel large-dial meat thermometer to accurately read the internal temperature of your 20 lb bird. You also pony up for a KIC Explorer with Navigator because you want to create the perfect deep-in spec reflow profile. It will not only tell you the specific temperature of the joints of your $500 BGAs, but it also will find a balance that does not overcook them or any of your other temperature-sensitive components on the PCB.  No pop-up indicator profiler needs to apply since the KIC Explorer with Navigator will go the extra mile and tell you not only if you are in-spec but how DEEP in-spec your profile is, along with what can you do to improve the profile in minutes, if not seconds.  Now do you know of any turkey thermometers that can do that?

So when you prepare your Thanksgiving turkey, and as you pause to give thanks, consider applying the same care and consideration that you have given to your family’s feast as you do to your PCBs.

Happy Thanksgiving – Profilingguru

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Reducing Reflow Product Changeover Time

2009 Presentation at SMT Long Island on how to reduce the changeover time from one reflow profile recipe to another.  If you ever opened up your reflow oven to dump all its heat to lessen downtime, this 4 min video is for you!!!

To view the complete video series (click here).

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

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Increasing Reflow Oven Throughput

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.

To view the complete video series (click here).

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

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Across the Belt Uniformity and Reflow Profiling

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.

Across the Belt Uniformity:

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).

BTU tool

Profiling for Reflow:

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.

PCB2

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).

PCB3

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:  http://profilingguru.com/reflow/profiling-bga-webinar/

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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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SMT related Links to know

RSS feeds, Tweets, blogs and newsletters, how do you keep up?   Well here is the latest on what’s available in the SMT industry.   I subscribe to all of these newsletters and regularly pick out areas of interest related to profiling for you.   I also comb the blogs though I only know of two, not including profilingguru, which is quite remarkable considering other industries have hundreds if not thousands.   The SMTA group forum on LinkedIn yields on occasion a nugget, but you need to build a profile to join.  SMTnet has always been a jewel.  Lastly, Twitter is a new phenomenon for many of us.   I am still trying to get the knack of it myself but it does have some value no doubt and will continue to grow.

On-line Newsletters:

Circuitnet

Electronics Production World

EMS Now

GlobalSMT

PCB Update

SMT Week

Blogs:

Circuits Assembly

Forums:

SMTA on LinkedIn

SMTnet

Twitter:

Circuit Assembly

Global SMT

SMT Magazine

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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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Save 15% in 15 minutes on your reflow’s energy consumption

Topic: 15% electricity savings in 15 minutes

Save Electricity in 15 mins. R0909B DRAFT

Date: Friday, September 25, 2009
Time: 1:00 pm, Pacific Daylight Time (GMT -07:00, San Francisco)
Meeting Number: 336 789 255
Meeting Password: (This meeting does not require a password.)

To join the online meeting
1. Go to https://kicthermal.webex.com/kicthermal/j.php?ED=107946437&UID=1013415122
2. Enter your name and email address.
3. Enter the meeting password: (This meeting does not require a password.)
4. Click “Join Now”.
5. Follow the instructions that appear on your screen.

Topic: 15% electricity savings in 15 minutes
Date: Friday, September 25, 2009
Time: 1:00 pm, Pacific Daylight Time (GMT -07:00, San Francisco)
Meeting Number: 336 789 255
Meeting Password: (This meeting does not require a password.)

——————————————————-
To join the online meeting

——————————————————-
1. Go to https://kicthermal.webex.com/kicthermal/j.php?ED=107946437&UID=1013415122
2. Enter your name and email address.
3. Enter the meeting password: (This meeting does not require a password.)
4. Click “Join Now”.
5. Follow the instructions that appear on your screen.

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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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