|Ask the Experts|
July 19, 2021
Baking After Cleaning Hand Placed Parts
Is baking required after in-line cleaning an assembly with moisture sensitive parts that were hand placed instead of through an SMT machine?
|Expert Panel Responses|
If a part is being placed by hand, instead of SMT due to moisture sensitivity, then it is been placed by hand to remove the automated wash step after SMT. The part will still be moisture sensitive and will require another means of cleaning or utilization of a no-clean flux in order to eliminate the cleaning process altogether.
This will depend on the cleanliness or post process requirements specific to the assembly. E.g. assume the assembly will need to be conformal coated, then there will need to be a means of cleaning off any excess flux residue prior to applying the conformal coat.
A second example, if the customer requires the use of a water soluble high activity level flux, then the flux will need to be removed. Best plan of attack is to work with the customer during the NPI phase and develop a process acceptable for the product needs.
Director of Corporate Quality Assurance
Delta Group Electronics Inc.
Moisture sensitivity is only applicable if you will heating (re-heating) the moisture sensitive parts again. If they have been soldered, and no other soldering (heating) is going to happen, then the components do not need to be baked.
M.O.L.E. Line Product Manager
Electronic Controls Design, Inc. (ECD)
Baking of moisture sensitive components is generally required before reflow soldering where the component body is exposed to elevated reflow temperatures.
Based on your question it appears as if your application is hand placing and manual soldering with a soldering iron. If this is the case you may not have to bake the components but it might be good to follow IPC baking guidelines to be on the safe side.
We would suggest that you bake after in-line and batch cleaning (minimum of 1/2 hour at 65C) to remove the moisture from under the SMT and connectors where moisture is easily trapped. This is what we do after the samples we run through our Aquastorm 200 with Paxton blowers, and IR heating. Still after the inline we can see moisture present at the edge of parts and weight studies before and after bake show a significant amount of moisture present after the inline.
President/Senior Technical Consultant
Any Moisture Sensitive component, which has exceeded its Floor Life, and will be subjected to a soldering process, must be baked prior to soldering. This includes components already soldered to a board (assembly) and then allowed to exceed their Floor Life. If these assemblies are to be reheated through a reflow soldering process (or process that heats the entire assembly to soldering temperatures), the whole assembly must be considered a Moisture Sensitivity component at the highest MSL of any single component on that assembly.
If the soldering process is a "hand" add soldering of additional components to an assembly whose previously soldered components have exceeded their Floor Life, you should be OK. Only those components being hand added must be "dry," having been handled in accordance with their MSL, ie: kept dry in their factory sealed bags for <=1 year, maintained dry in a dry storage cabinet or baked per the MSL requirements of J-STD-033. This is because "hand" soldering will only heat the added component sufficiently to be of any MSL threat; the surrounding components are not likely to get hot enough to be of concern.
As for cleaning the assembly after solder, whether this in any way accelerates the Floor Life clock, I'm not sure. The clock is running when the RH is >5% and full emersion in water (100%RH) for a few minutes is certainly >5% but only for a few minutes; the floor life of most MSL components is many hours or days, with the exception of MSL 6. If you intend to re-solder (heat the entire assembly to solder temperatures) an assembly, it will need baking only if that assembly exceeded the Floor Life of the highest MSL component on that assembly.
Senior Project Engineer
Electronic Controls Design Inc
Most inline cleaning systems utilize air-knife technology to blow-off water from the assembly after final rinse. Some inline machines add heat to the air-knifes that improve drying. I am not aware of any inline cleaning system that heats the assembly (board and components) to a high enough temperature for a long enough time required to remove entrapped moisture within components or the board.
I would recommend a bake-out procedure for any assembly which contains moisture-sensitive components or for any assembly that will be conformally coated or potted.
If one used a batch-cleaning system, then one could exaggerate the dry time and temperature to achieve bake-out results and possibly eliminate the need for a separate bake-out.
If this boards are not seeing another heating cycle later (like wave soldering), then you do not have to bake them. If not, monitor the exposure time and bake if necessary before other soldering processes. With this being said, I hope you've assured the components are ok (baked) before hand soldering them.
Engineering and Operations Management
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