We search for industry news, so you don't need to.
Ask the Experts  
Questions Index  ■  Submit a Question  ■  Experts Panel  ■  Join the Panel

December 4, 2017

Reflow Oven - 5 Zone or 8 Zone

We are a small electronics design company setting up an assembly line for small volume production. We prefer to purchase a 5-zone oven as cost is lower, but are concerned that 5 zones may not be enough to ensure a reliable reflow process comparing to an 8 zone oven.

Manufacturing volume is not a concern. Our boards are 5" x 7", components on both sides, component with largest thermal mass is inductor 10x10x6mm. Smallest components are 0.5mm pitch BGA, 0.5mm QFN and 0.65mm TQFP. Passives are 0603 imperial or larger.

For this board, would we see an actual difference in manufacturing process reliability between 5-zone and 8-zone ovens?

B.B.

Experts Comments

As long as you profile correctly it shouldn't really matter as we have many users, varied in size and complexities using 5 zone ovens. Obviously some ovens are better and more efficient than others so that would be my only constraint, make sure the oven is up to it in the first place. If the oven is ineffective then it won't matter how many zones you have. I recently witnessed a BOX Oven type reflow system with a profile of 27 minutes 40 seconds which gave understandably terrible results but once profiled and set correctly that produced the goods.
Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has twenty two years of service in Electronics industry. York has installed over 350 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

From a practical perspective, five (heating) zones is certainly enough, given that the length of the zones is configured properly. If the oven is configured with five equal-length zones, it may be difficult to achieve good control of liquidus time. Additionally, be sure that any oven purchased has a capable cooling section; if we can't cool adequately it will be very difficult to control liquidus time.

Best practice is to use your most difficult assembly to run profiles on candidate equipment, and select based on the ability to meet your desired profile with low measured delta-T. Not to say that thermal capability is the only factor to be considered, but it is the primary concern. For your lov-volume, low-mix application, you certainly don't need a high-end oven, but you will want more than an entry level machine if you want good process capability and reliability.

image
Fritz Byle
Process Engineer
Astronautics
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
In my opinion it would be best to spend the money on the 8-zone reflow oven in respect to the 5-zone. The future in our industry is lead free alloys. The profile for lead free can be easily be accomplished in an 8-zone reflow oven where is a 5-zone oven it will be difficult. Yes, you can set a profile for lead free in a 5-zone oven but you will have a much higher risk in maintaining a small delta "T" across the board. It is much easier to create a profile with 8 settings vs 5.
image
Michael Kaminsky
Sr Fiald Applications Support Engineer
Kester Inc.
Mr. Kaminsky has 30+ years of circuit board soldering assembly experience along with a patent for wave solder VOC flux process.
The answer is that the more zones you have, the more flexibility you have to tailor the reflow profile for best results (for through put and/or solderability). It is likely that a 5 zone oven with a forgiving solder paste could produce these boards defect free. The real question is if this board or paste changes next week, will you still be able to run it?
image
Mark Waterman
Engineer / Trainer
Electronic Controls Design, Inc. (ECD)
Mark Waterman is a trainer and field engineer with 17 years experience in service and applications specialties. Intimate knowledge of soldering processes and measurement systems. Six sigma and statistical process control generalist.

For the most part, ovens with more zones (thus longer length conveyors) allow you to increase the conveyor speed and a little more flexibility in the "shaping" of the "thermal profile" you may need for each assembly.

However, at the right conveyor speed (slower) a 5 zone oven will reflow the average sized/populated SMT assembly just fine.

image
Paul Austen
Senior Project Engineer
Electronic Controls Design Inc
Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 34 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, designer, manufacture, and customer. His focus has been the design and application of thermal process measurement tools used to improve manufacturing processes like: mass reflow and wave soldering, bread baking, paint and powder curing, metal heat treatment and more.

In the SMT process the 2 main pieces of equipment which have over 90% affect on the quality of a product are 1) Solder Paste Printing & 2) Reflow oven.

The type of reflow and number of zones of a reflow machine are dependent on ....

  1. Size of board .... the smaller the board the lesser time it would take to heat up the board and the larger the board the more time it takes to evenly heat the entire board and prevent a thermal shock which can lead to delamination.
  2. Number of layers .... very obviously the more the number of layers the more amount of heat would be required to raise the temperature of the board evenly across and get the right temperature on the pads.
  3. Amount of ground planes across the board .... this plays a very important role in the aspect of coefficient of thermal expansion. With patches of copper spread around for the ground planes, it's important to keep the heating of the board at an even constant rate.
  4. Types of components on the board .... the more mass the more absorption and also the type of packages - plastic versus metal versus ceramic.
  5. Density of the board..... how tightly are the components packed in a square centimetre of space. The more the number, more heat would be required.
Ofcourse, an important factor is which industrial segment are you catering to .... if you are catering to MacDonald tots segments one can settle for a 5 zone reflow but if you are catering to any other segment, it's always better to have a 8 zone reflow machine to be control your PWI within the acceptable limits.
image
Mahesh V Draksharapu
Independent Consultant

Over 28 years experience in the area of PCB assembly with 10 years working in various EMS companies in the US (Avex, GSS Array Technology now Benchmark, Everex computer Systems), 10 years working in OEM companies in the US (Trillium Test Systems, Intel & Meru Networks) and with Aristos EMS company in Bangalore since 2008. Engineering Degree from BIT, Mesra and Masters in Egg Mgmt from Wichita State University.

For modern quality reflow ovens, the longer ovens with more zones tend to be required primarily for higher throughput. If production volume is not an issue for you then most likely a 5 zone oven will suffice.

To be sure, however, you may want to profile a couple of your most challenging assemblies in a relevant 5 zone demo oven. If, after optimizing the oven setup, the profiles are close to the required process window limits, you may want to consider going to an oven with more zones.

image
Bjorn Dahle
President
KIC
Bjorn Dahle is the President of KIC. He has 20 years experience in the electronic manufacturing industry with various manufacturing equipment companies covering pick & place, screen printers and thermal process management.

Using an 8 zone oven definitely offers more flexibility in profiling.

However, a 5 zone oven can do a lot, especially in the hands of someone that is skilled in setting up profiles.

Your particular assembly does not sound especially challenging to profile. I would see if there is a way that you can try to profile your board on the 5 zone oven prior to purchase. It may be all that you need.

If you want something with more flexibility, that can address a more challenging future assembly, the 8 zone may be the way to go.

image
Eric Bastow
Senior Technical Support Engineer
Indium Corporation
Eric is an SMTA-certified process engineer (CSMTPE) and has earned his Six Sigma Green Belt from the Thayer School of Engineering at Dartmouth College. He is also a certified IPC-A-600 and 610D Specialist. He has an associate's degree in Engineering Science from the State University of New York and has authored several technical papers and articles.
I recommend using an 8 zone oven for lead free reflow profiles. A 5 zone oven will typically allow for simple linear ramp profiles, but soak profiles are difficult to program in a 5 zone oven. If you run mainly leaded solder with a linear ramp profile, then a 5 zone oven should work fine. Some solder pastes require soak profiles, so the choice of oven might depend upon the solder paste that you are using.
image
Tony Lentz
Field Applications
FCT Assembly
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.

This is one of those questions with multiple answers as the question can be interpreted in multiple ways:

1) Read as: "Would you see an actual difference in manufacturing process?"-the answer would be yes. By virtue of its additional zones, an 8 zone machine allows you to subdivide the profile graph into smaller sections. This allows you to "sculpt" the profile and have tighter control over aspects like dwell time and liquid time. In particular, a profile on an 8 zone oven may have a more pronounced "spike zone" with shorter liquid time where a 5 zone profile may look more like a "ramp" or "tent" profile that gradually climbs to the peak temperature and has a longer liquid time. Both systems however will have liquid times that meet solder paste specs.

2) Read as: "Would you see an actual difference in the manufacturing process reliability?"-the answer is most likely no. As always, results are dependent on the application but for the application noted here the results and reliability will likely be no different on a 5 zone machine vs. an 8 zone machine.

So a 5 zone machine can do the job. But a reflow oven typically stays in production for 7-10 years. Within the next 7-10 years it is likely that:

  1. Production will increase-with ovens, length = throughput so the 8 zone machine will have more throughput capacity vs. a 5 zone machine. You might outgrow the 5 zone machine as your business grows and have to buy a new machine in the future. The 8 zone machine will likely keep you going for the entire 7-10 year span. Often best to buy the machine you expect you WILL be needing vs. the one you need now.
  2. Board complexity will increase-more complex boards typically have more demanding profiles. The 8 zone machine will have the flexibility to create / sculpt the profiles that may come as new opportunities and customers come around.
A final thought. As a start-up, look around for a used 8 zone. You can get the growth and flexibility you need for the price of a new 5 zone. Hit up the manufacturer for a tune up with a refreshed warranty and away you go!
image
Marc Peo
President
Heller Industries Inc.
Mr. Peo has been with Heller Industries for over 20 years and has been President for the past 8 years. Marc has authored several industry articles on Soldering, Flux collection, nitrogen use and Lead Free conversion.

Difference between 5 and 8 zones ovens.

I do understand as I have been involved in design of smaller ovens exactly this size before.

The most important is the heating technology.
  • Older style manufacturers used a term IR (infrared radiation).

This is a generic term but needs to be understood fully as there are three or four types of IR, ceramic heaters, lamps such as quartz lamps similar to flood lights .

Then hot plates with holes that blow air through them.

  • The best technology today that everyone usually uses to describe the technology in ovens now ,is full convection hot air top and bottom as these can heat up fast not much mass and cool down faster than high mass heaters.

The reason that technology is the usually best is the heaters, as they do not contain any mass and can take care of different loads, conveyor speeds

One example would be different spaces between assemblies if hand loaded to belt on oven, but the temperature on the parts is the same as heater does not lose its heated mass, or take time to recover.

Back to length 5 or 8 zones.

I would thermocouple the front and back of the PCB and with some t/c on highest mass parts.

Connect to a profiler and monitor three or four PCB in each oven then pick the one with least delta T in temperatures.

One important point to remember is the PCB's described in your specification for deciding oven 5 or 8 zones are now, what happens in 5 years if same no issue.

As the time goes on technology increases maybe for you pitches go down which means more mass to assemblies, which then means more heat is required under better control (longer oven would be better in this situation).

When you decide to buy capital equipment of any type today most keep the products for ten years so a correct decision is very crucial.

Don't rush the choice and check how old the designs are that you are considering newer more efficient designs happen regularly.

Running costs

One last point is running cost consider how many BTU you burn an hour of running and how long to warm up before use.

With each oven you evaluate consider this, for the products as electricity is expensive these days so an efficient tool can also help pay for its self over a number of years.

image
Paul Wood
Advanced Applications Manager
OK International
Mr. Wood has been with OK International for 35 years and has been involved in the design of all rework products. He is a global expert in circuit board and electronics rework and has travel world wide supporting customer applications .
An age old question... How many zones do I need.. Speed, profile, components, etc. Personally I will defer to my esteemed college Phil Zarrow of ITM Incorporated for his response..
image
Jerry Karp
President
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.

If you are going to use lead free solder paste, minimum zone you need is 7. So Ho got 8 and you will be happier in the long run.

Can I make 5 zone oven work for a lead free board? Yes but if you change yo a complicated board in the future with components of different thermal masses, you will find it challenging to develop reflow profile

Do get scope of IPC 7530B for guidelines on developing reflow profiles. I chai this committee and this document was release earlier this year (2017)
image
Ray Prasad
President
Ray Prasad Consultancy Group
Ray Prasad is the founder of Ray Prasad Consultancy Group which provides teaching, consulting and technical expert services in tin-lead and lead free technologies using SMT, BGA, BTC, fine pitch and through hole components. Mr. Prasad is a long time member of IPC, and is currently the chairman of BGA committee IPC-7095 "Design and Assembly Process Implementation for BGA" and Co-Chairman of recently created IPC-7093 "Design and Assembly Process Implementation for Bottom Terminations" surface mount Components (BTCs) such as QFN, DFN and MLF.
A longer oven with more zones will provide more capability and flexibility to the reflow process. Meaning, assemblies with a wider variety of thermal mass can be processed with a wider range in each stage of the reflow process. The components you mention may require some profile refinement to achieve your desired outcome. For example, the QFN may require a soak to reduce ground pad voids and you may 'run out of runway' if the oven lacks sufficient thermal capability. Buy the biggest you can comfortably afford.
image
Tim O'Neill
Technical Marketing Manager
AIM
Tim O'Neill is the Technical Marketing Manager for AIM Products. AIM is a global supplier of materials for the PCB assembly industry including solders, fluxes and thermal management materials. Tim has a B.A. from Assumption College and post-graduate studies in education. He has 20 years of experience in the electronics soldering industry, beginning his career in 1994 with EFD and was key in business development of their fine pitch solder paste dispensing technology. Tim joined AIM in 1997 and has since assisted many clients with assembly challenges, specializing in Pb-Free process development and material selection.

Yes there is a difference between the two sizes of equipment, but the bottom line is capacity, as a 5 zone systems cannot process products as fast as the 8 zone system as the 8 zone systems allows faster conveyor speeds.

The most important issue is to develop a thermal profile for each side of your product, that's correct, two thermal profiles as the mass is different on each side of the board. Experiments will be needed to determine the temperatures in each zone and the conveyor speed to make sure the board completely reflows in the reflow zone of the oven. The initial thermal profile should be based upon the type of solder paste being used and the recommendations from the paste supplier, so you can set the oven temperature and conveyor speeds to meet those requirements.

I would recommend acquiring a thermal profile kit where the boards can have the thermocouples attached to it and have it also measure the oven temperature in each zone. This would provide you with information from the temperature in the oven and the temperature of the board, to determine the heat transfer from the oven to the board. This is how you would set the baseline profile.

Again the length of the oven is only for capacity. The important piece is the reflow of the solder joints within the reflow chamber of the oven.

image
Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
Submit a Comment

Your Name


Your Email


Company Name


Country


Comments




Authentication

Please type the number displayed into the box. If you receive an error, you may need to refresh the page and resubmit the information.