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January 21, 2026 - Updated October 8, 2013 - Originally Posted HASL Surface Finish and Coplanarity
We are an EMS contractor. We have a customer that has requested a PCB with HASL surface finish. This assembly includes a 256 ball BGA component. The component balls are 0.6 mm. Should we be concerned with coplanarity? Are there any other concerns?
T.Y.
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As has been said, a 0.60mm suggests quite a large pitch device. Previously, I would have said down to 0.80mm pitch BGA would be OK with HASL (assuming a well controlled process) but having seen issues on a part, would now recommend that 1.00mm pitch would be minimum.Anything below that wants to be a flat, planar surface which, due to the nature of HASL and physics, is not achievable and repeatable, without issue.
Technical Sales Manager, Fineline VAR Ltd
40 Years in PCBs. Large and small companies in the UK and the US. Experienced Process Engineer, DFM, Materials, Impedance Control, Surface Finishes, etc. Working with Fineline now across the portfolio of manufacturers covering rigid, flex, rigid flex, ATE, Load Boards, MSAP, and other existing and emerging technologies.
One of the HASL finish characteristics is variable thickness. This can cause co-planarity issues for BGAs as well as for other fine pitch multi leaded components. There are some solutions to alleviate this problem and the other comments covered them already. If it is a customer requirement, the tight tolerances at the PCB manufacturer would be your best bet.
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.
Hope you execute DFMA and its your responsibility to notify this risk to customer and latent failure risk if customer want to go with HASL on cost perspective. HASL do not have coplanarity very good and is highly variable, preference to be given to ENIG in case BGA <30mil pitch. Even nothing works to shift to ENIG, ask specification of coplanarity to be maintained with customer to deploy at PCB fabricator.
Supplier Quality Leader, Ge Healthcare
Subrat has 10 year of extensive experience in PCB assembly process optimizing for quality, process includes screen printing, wave, reflow. He has a copyright in stencil design published in Apex Expo2010 at Las Vegas US.
For BGA components down to about 0.8mm pitch, HASL is an acceptable finish. Your component, with a 0.6mm ball diameter, surely has a pitch larger than 0.8mm;it's most likely 1.0mm or 1.27mm. As an aerospace manufacturer, we do use SnPb HASL fairly regularly. We find that the (lack of) planarity is more of an issue on fine pitch (0.5mm, 0.4mm) leaded component lands than on 0.8mm pitch and above BGA lands.While HASL has its downsides, uniformity being one, the alternatives all have some downside as well. So as long as the PWB supplier is capable of maintaining a good process, you can certainly have success with the finish. All that said, the general trend seems to be away from HASL toward more planar finishes, though it may depend on who you ask. The "planar" finishes do enable more repeatable printing and placement for components with very fine pitch land geometries. At some point your customer may need to consider both the technical and supply-chain factors and decide whether HASL makes sense for their future. It's one thing if they are choosing HASL because of specific technical requirements, and quite another if they are choosing it because"that's what we've always done."
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.
HASL coplanarity will vary by method (horizontal vs. vertical) and by alloy (Pb-free versus SnPb). I'm sure you want repeatability; to that point here's the IPC's comment on the subject*:"Hot Air Leveling (HAL) or Hot Air Solder Leveling (HASL) processes are considered to have a degree of difficulty in their control.This, coupled with pad sizes and geometries placing additional challenges on such processes, places the creation of a practical minimum thickness outside the scope of this specification." Variable thickness, and lacking control thereof, can be seen as the root-cause of coplanarity issues. When it comes to playing the odds on terminal flatness consistency, HASL is your worst bet. * excerpt from IPC-6012, Qualification and Performance Specification for Rigid Printed Boards
President, Circuit Connect, Inc.
Bob has been in PCB design and fabrication since 1976. He has held elected positions with the SMTA, is a member of the MSD Council, has served as a committee member for various IPC standards and is a Certified IPC Trainer.
This is acceptable, but you will need to be placing the BGA with "Paste Additive"process. You should also ensure you have a PCB house that can ensure good HASL coverage with minimal crowning on the pads. This is commonly attributed to cleanliness prior to HASL application and some PCB houses are better than others at processing HASL.Another consideration is solder type. We would use Type IV powder with better than 90% solder content. This approach along with a extended soak in the liquidus phase helps to mitigate solder voiding that would be considered defects. Slowly ramping up temperatures in the active phase for the flux allows the volatiles to outgas and then extending the liquid phase encourages the voids to dissipate better in the solder pedestal of the BGA. PCB layout should be analyzed to provide consistent thermal dynamics as well. We preferred to have 4 quadrant escape patterns and I would not recommend 'via in pad' for this solder system, due to the time needed to soak the PCB. A good target for soak time was 3 - 5 minutes and Solder liquidus phase for HASL / Paste Additive described above for our production line is 7 - 10 seconds minimum.
Capital Equipment Operations Manager, Specialty Coating Systems
Rodney is currently Operations manager at SCS coatings, Global Leader in Parylene and Liquid Coating equipment. Rodney applies his BS in Computer Integrated Manufacturing from Purdue University, along with 20+ years of Electronic manufacturing and Equipment Assembly, to direct the Equipment business at SCS Coatings. "We provide unique, value added coating equipment solutions for our customers". Including conformal, spin and Parylene coating expertise.
Be concerned? Be afraid! Be very, very afraid!HASL was wonderful back when it was invented in the mid-70s for through-hole PCBs. With early SMT with 0.050" pitch components it was adequate. But once we went over the 0.025" pitch threshold, HASL floundered. It is about the most non-coplanar surface finish you can come up with. In these days of BTCs and area arrays, where every micron of solder paste thickness is crucial (as in make it or break it) the uneven topography of HASL just doesn't cut it. Consider any of the other surface finishes (ENIG, Immersion Ag, OSP - with their caveats) but unless you want a lot of headaches, skip the hassle with HASL.
Principal Consultant, ITM Consulting
Mr. Zarrow has been involved with PCB assembly for more than thirty years. He is recognized for his expertise in troubleshooting SMT manufacturing and lead-free implementation. He has extensive hands-on experience with set-up and troubleshooting through-hole and SMT processes throughout the world.
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