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

Profiling guidelines for reflow of solder bump flip chip attach to organic and/or ceramic packages

June 24, 2009 By Bjorn Dahle Leave a Comment

This post is in response to a suggested topic on this blog. The following answer was provided by Brian J. Toleno, Ph.D., Director Technical Service at Henkel:

When profiling a flip-chip to an organic substrate you typically want the delta T across the component to be as low as possible in order to minimize stresses and warpage. Of course, like any good profile, making sure that the solder bumps and solder paste reach liquidus, stay above the liquidus temperature for the recommended time, and have a controlled cool down as possible are key. In addition, if the flip chip device is going to be underfilled, then it is important that when using a no-clean flux solder paste that the solder paste is fully activated in order to minimize any possible flux/underfill interactions. So making sure you measure the temperature at the flip-chip bump/solder paste/solder pad area is important. You also want to make sure you measure the temperature at the centre and the corners (making sure they track close together). While there typically is not as great of a chance of a large delta T, like there would be in a BGA or CSP device – when one does occur it can be more catastrophic.

Filed Under: Define, Reflow Tagged With: BGA, BGA Profiling, ceramic packages, defect rates, efficiency, electronics manufacturing services, flip chip, profiling, Reflow, reflow profiling, SMT and standards, surface mount technology, thermal process, 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

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

Thermocoupling BGA

March 28, 2009 By Bjorn Dahle Leave a Comment

Perhaps the most challenging components to thermocouple are BGAs, since the area of reflow is hidden underneath the component. The most accurate methodologies are destructive. The simplest way to thermocouple a BGA may be to drill a hole on the underside of the BGA and thread the TC bead into the drill-out hole that allows access to the target area without having to remove and re-attach the BGA.

Another method is to use a very thin gauge TC wire (40 AWG) and separate the two dissimilar wires, as shown below. Then attach the TC and place the BGA on top of the TCs. Again, the point of this exercise is to achieve an accurate “direct” reading.

Special thanks to Scott Nelson at Harris Corporation for providing this example.

A non-destructive method for thermocoupling BGAs is to simply mount the TC on top of the BGA and, perhaps, to the underside of the PCB directly below the BGA, and develop an offset. There is no right or wrong answer; much depends on your production tolerances and a whole host of other variables that have been discussed in this guide. The point is that only you know your process and limitations with respect to product and tools.

Note: This is an area of particular interest to me since it is a concern that just about everyone has an opinion on and no true right or wrong way has been developed. Stay tuned more to come soon.

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

What is a baseline profile?

March 28, 2009 By Bjorn Dahle 2 Comments

Baseline profiles are used purely for set-up purposes. They are manually-fed into the reflow oven and are run in tandem with a monitoring system in order to create what is called a “virtual profile.” Baseline profiles, thus, become the standard by which all automated profiles are compared. If there are any deviations between the baseline profile and the automated profile, this information is recorded and can trigger alarms and stop production temporarily. Baseline profiles also have the added advantage of becoming a true “gold standard” for all of your profiles, since the same profiling board is not being used repeatedly or subject to degradation of the PCB, thermocouples or operator error.

The set-up of a baseline profile is performed by running a normal profile, per recipe. Meanwhile, 1-2 fixed mounted probes (typical an array of 15-30 thermocouples) collect their own set of data as the PCB runs the length of the Reflow oven with a profiler. This information is then compared and processed by the monitoring system. This array of internally-mounted thermocouples is able to reconstruct a virtual model of a profile. When a production board enters, without the profiler, the same TC readings that were present when your oven was profiled are now re-mapped onto each and every PCB.

Filed Under: Automation, Reflow, TC's, Types of Profiles Tagged With: BGA, cost-based tools, defect rates, efficiency, profiling, Reflow, reflow oven, reflow process, reflow profiling, SMT, SMT and standards, soldering, surface mount technology, thermal process, thermal profiling

Getting your Product Deeper in Spec | Profiling Software

March 28, 2009 By Bjorn Dahle Leave a Comment

Q: What happens when defects occur when the thermal load on the oven increases? Do you slow down production? Do you change the oven set points by cranking up the heat to compensate for the increased load?

A: The answer is to establish a NEW profile that is deeper in spec., a profile that is able to better stand up to the daily variations of a reflow process.

Today, profiling software allows you to establish these new deep-in-spec profiles with relative ease. You can precisely define your specifications and run various predictive scenarios. For example, you know that you can’t slow down your conveyor speed, but you can change your oven set points. The profiling software can give you a predictive result that puts you as deep in spec as possible before ever having to run a profile.

In practice, how much work needs to be done to take this out-of-spec process and bring it within spec depends on a lot of factors. How far out of spec are you to start with? What inputs can be changed? How tight are your specs?

If your process is already taking up most of your process window or not far out of spec, then only minor changes will most likely be needed to bring your profile much deeper into spec. In this case, only one additional profile is likely required to bring your profile very deep within spec. In my experience, this profiling process takes about 30 minutes, most of which is waiting for the oven to cool. If your profile is far out-of-spec., you may need up to an hour to bring it within spec.

Each time you re-profile, it is an opportunity to further improve your profile, bringing it further into spec with each effort. Profiling software will tell you a possible scenario for improvement each time, which takes your excellent deep-in-spec profile still deeper within spec. Each one of these changes, on average, takes about 30 minutes.

A word of caution: having a profile in the center of the spec or at 0% PWI, is not always the optimal improvement. While “0%” PWI is statistically desirable, there are other factors to consider. For example, though 30% PWI indicates that you are only utilizing 30% of the allowable process window of your solder paste, in practice, when you find that a PWI of 65% produces a physically better connection, which is better? Specs are just that: specs. They have a range for a reason. In this case, at the upper end of the spec (opposed to the center of the range), a joint may solder better. Advantageous about most profiling software is that you can go back and re-define your specs to see what your new profile will look like without having to rerun the profile. The allowed range can be further narrowed to a particular spec, which results in a better joint. In essence, you are now re-defining your spec, and all future profiles will only consider this new range.

Filed Under: Define, Improve, Reflow, Types of Profiles Tagged With: BGA, cost-based tools, defect rates, efficiency, Process Window, profiling, profiling software, Reflow, reflow oven, reflow ovens, reflow process, reflow profiling, SMT and standards, soldering, surface mount technology, thermal process, thermal profile, thermal profiling

Components

February 26, 2009 By Bjorn Dahle Leave a Comment

Paste specs will typically exceed those of components, therefore, much thought is typically not given to component specs until they are literally flying off your PCBs. Like PCBs, the material of the components plays a role. I’ve seen more time and effort spent on profiling ceramic packages than I care to remember. When you have a capacitor close to a large ceramic BGA, how do you get the BGA to reflow and still keep the capacitor from looking like popcorn? One common technique is to isolate each component with its own individual process spec and then run this new setting through the profiling software prediction, as discussed in this prior. The profiling software will tell you if it is possible to achieve what you want with your given board, paste and oven. Solutions to shield sensitive components and a complete re-design may also be in order. Additionally, the solution might be that you need new equipment that can follow the new process recommendations, allowing for tighter controls and/or more zones. Your profiler will calculate the possibilities.

Filed Under: Define, Improve, Reflow Tagged With: BGA, ceramic packages, cost-based tools, defect rates, efficiency, electronics manufacturing services, Process Window, profiling, profiling software, Reflow, reflow ovens, reflow process, reflow profiling, SMT and standards, soldering, surface mount technology, thermal profile, thermal profiling