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April 10, 2018

Baking Concerns for Stacked Trays of Components

When we are baking multiple trays of parts stacked on top of each other in our oven, will this lessen the effect of baking on the components in the middle trays. Do the trays need to be separated?  We bake our components according to IPC specifications.


Experts Comments

My suggestion would be to stack the trays, so air can circulate over the components of each tray to insure all the components are exposed to the same temperature and air flow.
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.
All moisture sensitive devices (MSDs) such as QFPs, TQFPs, TSOPs, etc. need to be baked before soldering based on their moisture sensitive level (MSL) number in accordance with IPC/JEDEC standard J-STD-003A. The time and temperature of the baking cycle is generally dependent upon the device thickness and the distance between the lead-frame and the plastic body. Most baking ovens allow multiple trays of devices to be stacked inside the oven on slots that leave a gap between each tray. As long as the vertical distance between trays does not impede the airflow within the oven, stacking multiple trays should not impact the baking process.
Carlos Bouras
General Manager
Nordson SELECT
Carlos Bouras is the General Manager of Nordson SELECT and has over 30 years of experience in the electronics manufacturing industry. Carlos's expertise is in process engineering, product development and manufacturing operations. For the past 15 years Carlos has focused specifically on automated assembly issues and is the holder of several US patents for non-contact dispensing and precision dispensing of adhesives for the packaging of microprocessor devices.
We also bake parts out on a regular basis and I assume you are using standard trays which stack and inter-nest.  We have seen no negative impacts from parts baked out in the inside trays or the bottom trays. We performed a test to see or test for impact and we found no negative trends. I will advise the volume of trays should be considered on when the parts all reach temperature which will be based on load and volume of trays and the official bake time only starts when all parts or trays reach temperature.

We take that into consideration to insure the bake out times reach peak temperature before the clock starts. No knowing the part types or tray style - I would recommend performing a DOE test and track the parts for bake out yield efficiency. We did that DOE so that we would have objective evidence for our end customer to insure our bake out procedure did not introduce any negative impacts on the end product.
Mark McMeen
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.
I would think the air circulation in the oven is critical so it moves over all the products being baked in the process of removing the moisture. The second point I would consider, is the thermal mass of all the boards in the oven and the time it will take the oven to stabilize the temperature for that particular load. I would make sure my time count starts when all the product is at temperature, not when they are put into the oven.
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.
You need to ensure that there is enough heat flowing through the trays.  If they are too close to each other you might not get the desired effect in the middle trays.  Perform a small experiment comparing the pin-hole or void occurrences between top, bottom and middle trays. The results will help you determine the optimal spacing between trays.
Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
Space constraints might require stacking the trays on top of each other. As the trays geometry differ, assuring that air flow happens on each trays stack (there are spaces for the air to flow in between components) than you should be ok. However, if the tray design does not have any openings in between components/components individual locations, then you are running some risk that the parts in the middle might not see all the heat needed. You can compensate that with baking time but there is no magic formula for that. Assuring that part exposure to heat is done is the best way to set for a successful process.
Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at georgiansimion@yahoo.com.
The parts in the middle will not see the same air flow like the ones that are towards the outside. Baking the parts to the IPC specification should suffice.One recommendation for this process is to leave space in between the different tray stacks to assure air flow from the sides of the trays

When we are baking multiple trays of parts stacked on top of each other in our oven, will this lessen the effect of baking on the components in the middle trays. 

Do the trays need to be separated?  We bake our components according to IPC specifications.
Georgian Simion
Engineering and Operations Management
Independent Consultant
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at georgiansimion@yahoo.com.
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