Plugging the Hole in the SMT Reflow Inspection Process

August 20, 2009 By Bjorn Dahle Leave a Comment

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

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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Filed Under: Automation, Process Window, Reflow Tagged With: AOI, BGA, BGA Profiling, cost-based tools, defect rates, efficiency, electronics manufacturing services, energy efficiency, Process Window, profiling, Reflow, reflow oven, reflow ovens, reflow process, reflow profiling, SMT, SMT and standards, SMT Reflow, soldering, SPI, surface mount technology, thermal process, thermal profile, thermal profiling

BGA Profiling Webinar Recording

July 31, 2009 By Bjorn Dahle Leave a Comment

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).

Podcast: Play in new window | Download (Duration: 8:00 — 50.7MB)

Filed Under: Automation, Define, Improve, Measure, Podcasts, Reflow, TC's Tagged With: BGA, BGA Profiling, cost-based tools, defect rates, efficiency, electronics manufacturing services, profiling, Reflow, reflow oven, reflow process, reflow profiling, SMT and standards, soldering, SPI, surface mount technology, thermal process, thermal profiling

Energy Consumption Reduction for Reflow | Better Thermal Management

July 21, 2009 By Bjorn Dahle Leave a Comment

Is your reflow oven throwing money away with a poor thermal management?

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

Podcast: Play in new window | Download (6.4MB)

Filed Under: Improve, Measure, Podcasts, Reflow Tagged With: cost-based tools, defect rates, efficiency, electronics manufacturing services, energy efficiency, profiling, Reflow, reflow oven, reflow process, reflow profiling, SMT and standards, soldering, surface mount technology, Thermal Management, thermal process, thermal profiling

How to Maximize Reflow Ovens Throughput

July 21, 2009 By Bjorn Dahle Leave a Comment

The following video shows you how to in the fewest steps possible in the least amount of time increase your reflow ovens throughput while maintaining an in-spec process. In this real life example, throughput was increased by 20% in 20 minutes time!

Filed Under: Characterization, Improve, Measure, Podcasts, Reflow Tagged With: cost-based tools, efficiency, electronics manufacturing services, maximize throughput, profiling, Reflow, reflow oven, reflow ovens, reflow process, reflow profiling, SMT and standards, soldering, surface mount technology, thermal process, thermal profiling

Profiling BGA Webinar

June 24, 2009 By Bjorn Dahle Leave a Comment

Profiling BGA Webinar Supplemental (July 1, 2009):

Component Specific Specs

We discussed the need to define BGA specs separate from other components that have different reflow requirements. BGAs typically require more heat to reflow properly but typically there are many other “smaller” components that also populate a PCB that will overheat if you develop your process solely around the BGA. The following 2:40 min video reviews how you can bring both your BGAs and other temperature sensitive components into spec, striking a thermal balance that results in quality products.

Thermocouple Attachment

The following 1 min video shows one of the most reliable direct methods of TC attachment for BGA profiling.

…..but, who can always sacrifice a PCB in the process? We talked about some indirect/non-destructive methods for profiling BGAs that are suggestive, but inconclusive. In the fall I hope to have some results of a study that will help our industry come up with solutions that one can reasonably predict the temperature/profile of a BGA without destroying the PCB in the process or worse the BGA!

BGA Inspection

First there was SPI (solder paste inspection), then there was AOI, now there is RPI (Reflow Process Inspection)

rpi-smt-linerev-11

You can see a prior blog posting discussing RPI at: http://profilingguru.com/reflow/what-is-reflow-process-inspection/

RPI works in the world of continuous reflow monitoring, where a profile is created for each and every production board.

In order to automate reflow profiling, a baseline/virtual profile is first established, where one runs a traditional profile with PCB, TC attachment and profiler while the on-board system of 30 thermocouples gathers the same profiling data and reconstructs and converts the traditional profile to a virtual representation. Once a virtual profile has been established, profiles can be collected for all production boards. SPC charting, cPk, traceability and process control are all possible.

So rather then the reflow process being a black box, where anything and everthing can go wrong…..

illustration_5 ….alternatively, do you not only know what is going on continuously, but your BGAs using the techniques above are being monitored on a continuous basis.

reflow-yield_3in_nk

Your Questions:

Q: Doesn’t the thermocouples utilized by the oven itself (assuming that they are calibrated and verified) provide the same basic information as the secondary set of TCs you are referring to?

ANSWER: No, the oven thermocouples and the secondary KIC TCs have completely different and separate functions. The oven TCs are typically located close to the heaters since their job is to turn the heaters on and off as the temperature drifts from the set points. The KIC 24/7 (or KIC Vision) TCs, located along the conveyor, help to automatically measure the profile that each PCB experiences as it is processed through the reflow oven or wave solder machine. This function is called Virtual Profiling.

Virtual Profiling (VP) provides process traceability as it logs the profile for each PCB, along with information on how this profile fits the established process window. The VP works in real time and offers instant alarm when the process (profile) drifts out of spec. Because it provides basic SPC charting, it acts as an early warning system for trouble ahead. Think of the KIC24/7 or KIC Vision as an automatic profiling system in real time.

Q: I encountered wetting issue with CSP and BGA, how do I solve them? / Q: How about wetting issue?

Answer; In some cases, but of course not all cases, wetting issues are a result of incomplete flux activation in the solder paste and an overall low temp soak, where the components did not reach sufficient energy levels before entering the reflow, TAL stage of the process. Many of these issues are related to Pb – free solder pastes, mixed RoHS components or a number of other variables.

I suggest that the best answer is to research the publications available on the Web for the most relevant solution. The following is a link that closely resembles the issue, but again, you will need to research the most relevant to your situation.

http://www.emsnow.com/cnt/files/White%20Papers/Henkel_Leadfree_Designing_Reliability.pdf

Q: How do you take measurements on each board without TCs?

Answer: KIC software algorithms compare what was observed at the time of the Baseline Profile to what is present within the oven during production. Using the 30 thermocouples in the oven, this data is communicated to the eTPU and the output is the PWI based on the specific process and the specification of that process.

Q: How well does the DPMO relate to the actual defect where there could be placement defects interacting with reflow?

Answer: DPMO is a parameter of only the thermal reflow process. If issues exist in placement or screen printing, it will not be reflected in the DPMO, since KIC is only monitoring the thermal process. Given that all other aspects of the SMT line is functioning properly, DPMO will give an assessment of the thermal defects assuming that the proper solder paste and placement is present at the time the product enters the oven.

Q: What about paste formulations?

Answer: KIC works with any solder paste manufactures to build the solder paste library that is present in the KIC software. This library is updated periodically and verified by the solder paste manufactures in most instances. The library however does not at any one time contain all information about all possible solder pastes. We try our best to be certain the information is present, but changes in formulation and engineering at the solder pate manufactures sometimes causes gaps that are beyond our control.

Q: How important is it to drill into the BGA ball and put the TC in it, vs. putting on the package, slip under the package, and on the bottom side of the board?

Answer: There are many variables in PCB design and component placement that directly and indirectly affect other components, in this case BGA. The best possible answer to this question is in the amount of data that is collected, how it is collected and how this information is applied to the specific PCB and BGA directly. Gathering as much information as possible, charting this info and drawing data driven values is the best possible formula for successful BGA reflow. Using all available data collection methods and positions aids in successfully reflowing this package.

As indicated during the webinar, we are currently commissioning a study to see if non destructive methods can be used in place of drill a hole.

Q: Does your software always choose an extended peak recipe?

Answer: No. Based on the type of recipe and profiles that are part of your normal production determines what path the KIC Navigator (auto-prediction) directs the profile. If your profiles are mainly RTP, the software looks at the values of the library data and suggests set points that will lead to a RTS profile. If your profiles are largely RSS, then the suggested set points will tend towards a RSS profile.

Filed Under: Define, Improve, Measure, Reflow, TC's Tagged With: AOI, BGA, BGA Profiling, cost-based tools, defect rates, electronics manufacturing services, Process Window, profiling, Reflow, reflow oven, reflow process, reflow profiling, SMT, SMT and standards, SPI, surface mount technology, thermal process, Thermal Process, thermal profiling, thermocouple attachment

How to add a Component Specific spec to a Profile

June 14, 2009 By Bjorn Dahle Leave a Comment

What do you do when you have temperature tolerant components on your PCB that require a different reflow profile?

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

Podcast: Play in new window | Download (10.2MB)

Filed Under: Improve, Podcasts, Reflow Tagged With: AOI, defect rates, efficiency, electronics manufacturing services, profiling, Reflow, reflow oven, reflow ovens, reflow process, reflow profiling, SMT and standards, soldering, surface mount technology, thermal process, thermal profile, thermal profiling

What is Reflow Process Inspection?

June 1, 2009 By Bjorn Dahle Leave a Comment

Reflow Process Inspection is catching on as the next advancement in-line inspection systems for SMT Reflow. I have pulled together the various aspects of RPI to better explain how it works and what are its benefits.

How does RPI fit into the inspection processes in the SMT factory?

Unlike SPI and AOI that are defect inspection systems specifically designed for viewing solder deposition and component assembly respectively, RPI complements these systems by inspecting the performance of the thermal process IN-LINE. RPI inspects the thermal process for any joint, including those that are not visible to the AOI system such as BGA components.

What is being measured?

RPI charts the thermal Process Yield and DPMO

What are the RPI benefits?

RPI provides information on the “health” of the thermal process over time. The Yield and DPMO charts provide instant understanding of detrimental changes in the process. The following format is easy to read and understand and often used by management as well as engineers.

dpmoyield1

For an Overview:

Awards for RPI:

2009 Innovation Award

KIC’s RPI Wins a 2009 NPI Award

Innovative Technology Center Award at Apex 2009

Filed Under: Automation, Featured, Improve, Reflow Tagged With: AOI, BGA, cost-based tools, defect rates, electronics manufacturing services, profiling, Reflow, reflow oven, reflow process, SMT, SMT and standards, SMT Reflow, SPI, surface mount technology, thermal process, thermal profiling

Is there a standard calibration tool for the reflow process?

May 28, 2009 By Bjorn Dahle Leave a Comment

A question was posted on Circuitnet (May 18, 2009) asking if there is a standard test board that can be used for profiling/calibration of a reflow oven. Answers were provided by profiling companies, oven and rework station manufacturers.

The consensus from all groups was:

There is no standard test board.
There is no substitute to creating an actual profile of your product.

Here is a summary of panelist replies, including from yours truly (for a full transcript go to http://www.circuitnet.com/articles/article_59131.shtml).

Brian O’Leary – KIC (full version)

The short answer to your question is no. There is no industry standard test board.

Test boards, also sometimes called “golden boards,” are an imperfect measure. Often, they are used for calibration purposes, but keep in mind every time you run the same PCB through an oven, some mass of the board is lost. For this reason, a true GOLD standard that is identical to your production board is difficult to achieve, unless you can somehow recreate the exact same conditions each and every time you profile your standard test board.

Since PCBs lose mass, some manufacturers will create calibration tools out of plates of stainless steal and use metal slugs to simulate components. Of course, a hunk of metal is no closer to a production board than a golden board, but at least it gives you a relative measure that is repeatable.

So what is the best answer if there is no perfect tool? There is no better representation of what is going on with your Reflow process than running an actual profile of a production board. The good news is that there are tools available that do not necessarily mean running a profile equals destruction of a sellable product nor does it mean that you need to waste the next few hours profiling.

Both oven manufacturers and profiling companies have developed onboard databases that allow you to develop in-spec profiles before you even profile (see this link) so when you run a verification profile you can at least do so knowing that the PCB being used can still be sold!

Another method of ensuring your process is continuously in spec and can serve as an early warning if things are going astray is the use of systems designed to monitor your oven.

For example, KIC’s 24-7 and Vision will create virtual representations of your PCB all based off of a true “golden board,” since the PCBs used to set up the system to create these virtual profiles are run through your process as actual profiles. As an added bonus, these same boards do not suffer from the repeated use problem described above with golden boards.

Fred Dimock – 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. The test board might match a small percentage of boards actually being produced but is not close to many more and is not intended for calibration.

….I have personally seen companies place unrealistic performance specifications on reflow oven testing with 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….

Richard Burke – Datapaq

First of all, nothing can take the place of running profiles of your actual PCB’s…..

…There is really no industry standard test board available……to suggest otherwise would be dangerous whereas this would assume that all assemblies are identical and this is not the case. If you set the oven up to the test board, it would invariably be different than your own assemblies. This is not a risk worth taking.

Al Cabral – VJ Technologies

Test boards can be created to illustrate specific characteristics of a reflow system, be it heating / cooling capacity, thermal repeatability, thermal uniformity across a conveyor system or designed to emulate a particular type of product.

It’s very difficult for one test vehicle to do it all well. A test board supplied by an oven manufacturer or independent supplier will likely address one or two of the aforementioned.

For example, a test vehicle designed to compare several ovens across multiple lines can be vastly different from a test vehicle designed to measure cross belt uniformity. Similarly, a test vehicle designed to gauge percent infrared, may not be well suited for CpK measurement.

Filed Under: Characterization, Improve, Reflow Tagged With: cost-based tools, defect rates, efficiency, electronics manufacturing services, profiling, Reflow, reflow oven, reflow ovens, reflow process, reflow profiling, SMT, SMT and standards, SPI, surface mount technology, thermal process, thermal profiling

Process Window Index

May 11, 2009 By Bjorn Dahle Leave a Comment

Each thermal profile is ranked on how it fits in a process window (the specification or tolerance limit). Raw temperature values are normalized in terms of a percentage, relative to both the process mean and the window limits. The center of the process window is defined as zero and the extreme edges of the process window are ±99%. A PWI greater than, or equal to, 100% indicates that the profile does not process the product within specification. A PWI of 99% indicates that the profile processes the product within specification, but that it runs at the edge of the process window. For example, if the process mean is set at 200 °C, with the process window calibrated at 180 °C and 220 °C, respectively; then a measured value of 188 °C translates to a process window index of -60%.

By using PWI values, manufacturers can determine how much of the process window a particular thermal profile uses. A lower PWI value indicates a more robust profile. For maximum efficiency, separate PWI values are computed for peak, slope, reflow, and soak processes of a thermal profile.

To avoid the possibility of thermal shock affecting production, the steepest slope in the thermal profile is determined and leveled. Manufacturers use custom-built software to accurately determine and decrease the steepness of the slope. In addition, the software also automatically recalibrates the PWI values for the peak, slope, reflow, and soak processes. By setting PWI values, engineers can ensure that the reflow soldering work does not overheat or cool too quickly.

Example of a Process Window Index for peak, soak, and slope values

The Process Window Index is calculated as the worst case (i.e. highest number) in the set of thermal profile data. For example, a thermal profile with three thermocouples, with four profile statistics logged for each thermocouple, would have a set of twelve statistics for that thermal profile. In this case, the PWI would be the highest value among the twelve values, expressed as a percentage. The formula to calculate PWI is:

where:

i = 1 to N (number of thermocouples)

j = 1 to M (number of statistics per thermocouple)

measured value [i, j] = the [i, j]^th statistic’s value

average limits [i, j] = the average of the [i, j']^th high and low limits of the statistic

range [i, j] = the [i, j]^th high limit minus the low limit of the statistic

Thus, the PWI is the worst case profile statistic that is the maximum, or highest percentage of the process window used.

^{Source: Wikipedia: http://en.wikipedia.org/wiki/Process_Window_Index}

Filed Under: Process Window, Reflow Tagged With: cost-based tools, defect rates, efficiency, electronics manufacturing services, Go no go, Process Window, profiling, Reflow, reflow oven, reflow profiling, SMT and standards, soldering, surface mount technology, thermal process, thermal profile, thermal profiling

Soldering and Profiling Discussion Panel at Apex 2009

April 30, 2009 By Bjorn Dahle Leave a Comment

Panelists at APEX discuss misconceptions about the reflow process and how to Minimize Delta Ts, etc.

Mike Buetow of Circuits Assembly magazine moderates a discussion panel on soldering and thermal profiling at APEX 2009. Panelists include Keith Howell of Nihon Superior, Fred Dimock of BTU and Michael Limberg from KIC.

Much of the 30 min discussion hits upon how customers often confuse an oven’s recipe with a PCB’s profile/recipe. Factors such as density, delta Ts, belt speed, different components and extraction are used as examples as to why the oven’s set points don’t always match the temperatures on the PCB. All panelists agree that a fair amount of customers do not understand these important concepts.

Fred Dimock of BTU cites an interesting study he conducted to highlight the difference mass has on the peak temperatures a board experiences without changing the oven set points. The example he gives is a 100gram board that achieves a 231 C peak when compared with a 230gram board only reaching a 225C peak with everything else being equal. Panelists agree that customers often expect to see the same profile at a given oven set up, when obviously factors such as mass play such a critical role!

All panelists talked at length about how to minimize delta Ts as an important factor in producing quality PCBs. The PCB design and layout of components was discussed by Keith and Mike.

Fred cited a study that higher convection rates also yield a lower delta T, taking into account the need to maintain a stable environment early on in the reflow process before components have had a chance to take hold. Starting at low convection allowing the flux to become tacky (thus keeping components in position) and eventually raising convection in the peak zone can minimize large deltas.

Fred also shared a profiling trick with Ramp Soak Spike profiles he likes to use when trying to minimize the delta Ts at peak. In RSS profiles, one would run as close to the edge of the top of the spec of soak and get as high as you can in temp early before you hit the spike, but you need a quality profiler and good ThermoCouple attachment to pull this off, Fred added.

The session also covered briefly upon topics such as:

Vapor Phase profiling: Keith & Mike
Nihon’s SN100C paste: Keith
How to Profile Expensive Components: Mike
Importance of Cool Down and considerations, such as the roll of large BGAs: Fred and Keith

To watch a video of the session, click here: http://blip.tv/file/1969267/

Filed Under: Featured, Reflow, TC's Tagged With: BGA, cost-based tools, defect rates, efficiency, electronics manufacturing services, profiling, Reflow, reflow oven, reflow process, reflow profiling, SMT and standards, soldering, SPI, surface mount technology, thermal process, thermal profiling, thermocouple attachment

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

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?

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?

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?

Awards:

Profiling BGA Webinar Supplemental (July 1, 2009):

Component Specific Specs

Thermocouple Attachment

BGA Inspection

Your Questions:

Q: Doesn’t the thermocouples utilized by the oven itself (assuming that they are calibrated and verified) provide the same basic information as the secondary set of TCs you are referring to?

Q: I encountered wetting issue with CSP and BGA, how do I solve them? / Q: How about wetting issue?

Q: How do you take measurements on each board without TCs?

Q: How well does the DPMO relate to the actual defect where there could be placement defects interacting with reflow?

Q: What about paste formulations?

Q: How important is it to drill into the BGA ball and put the TC in it, vs. putting on the package, slip under the package, and on the bottom side of the board?

Q: Does your software always choose an extended peak recipe?

How does RPI fit into the inspection processes in the SMT factory?

What is being measured?

What are the RPI benefits?

For an Overview:

Awards for RPI:

Brian O’Leary – KIC (full version)

Fred Dimock – BTU

Richard Burke – Datapaq

Al Cabral – VJ Technologies

Panelists at APEX discuss misconceptions about the reflow process and how to Minimize Delta Ts, etc.

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