|Ask the Experts|
June 3, 2019
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 largestthermal 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?
|Expert Panel Responses|
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.
Technical Sales Manager
BLT Circuit Services Ltd
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 low-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.
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.
Sr Fiald Applications Support Engineer
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?
M.O.L.E. Line Product Manager
Electronic Controls Design, Inc. (ECD)
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.
Senior Project Engineer
Electronic Controls Design Inc
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 ....
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.
inspīre solutions LLC
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.
Technical Support Engineer
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.
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:
Heller Industries Inc.
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.
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.
Advanced Applications Manager
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.
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)
Ray Prasad Consultancy Group
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.
Technical Marketing Manager
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.
Vice President, Technical Director
Personally, I would recommend the 8 zones.
The population on the board is a good criterion to understand the technical equipment capabilities necessary to build the product, however the internal structure of the board is important too. Also you do not want to limit your capabilities for the future on what challenges you can take on.
Engineering and Operations Management
|Submit A Comment|
Free Newsletter Subscription
Circuitnet is built for professionals who bear the responsibility of looking ahead, imagining the future, and preparing for it.
Insert Your Email Address