Implementing Robust Bead Probe Test Processes
Via-In Pad Plated Over (VIPPO) Design Considerations
Screening of Lower Melting Point Pb-Free Alloys
Condensation Testing - A New Approach
Case Study for Improving the PCB Print Process Using Factory Data
DFX on High Density Assemblies
Improved SMT and BLR of 0.35 mm Pitch Wafer Level Packages
Wetting and Solidification of Pure Tin on Polycrystalline Intermetallic Substrates
Latest Industry News
MacBook, iPad Production Delayed as Supply Crunch Hits Apple
Microsoft unveils liquid cooling solution for datacenters
A Theory of (Almost) Everything
Toyota unveils new models in advanced driver-assist technology push
Tech Giants Enter Their Chips in the Race for Self-driving Cars
What will self-driving trucks mean for truck drivers?
4 Great Things That Happened When We Went Remote
iPhone 13 is going to be worth the wait: All the major upgrades we're looking forward to

Risks Using Flux Only for Soldering BGAs

Risks Using Flux Only for Soldering BGAs
What are the risks using flux only versus solder paste for placing BGAs in a hybrid lead-free environment? Why would you only use flux, why not solder paste?
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.



And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers, who by day go as ITM Consulting. We are here to address your problems, questions and situations with regard to the surface mount and through-hole assembly processes.

We have a surface mount process today, Jim. This is from C.C. C.C. inquires, what are the risks using flux only versus solder paste for placing BGAs in a hybrid lead-free environment? Interesting question. I guess the first thing that I would ask is why would you only use flux, why not solder paste? Is this a rework situation? Are we economizing here? Maybe, the cost of solder paste is certainly going up. I am wondering what the motivation is.


I agree. I am concerned about this word hybrid. In a hybrid, lead-free environment. I don’t know what that means, so I will ignore it. I agree with you. It is very common in rework to use flux only. We have talked about repairing BGAs and many practitioners have written in the comment section, which all of you out there should be checking if you are interested in one of our questions.

Our listeners and readers are often sending in some very good advice. A lot of people who are actively doing a lot of BGA rework said no we use flux only, it is much better. It would be rather problematic to use flux only in a straight reflow because you have to get a stencil without holes, apertures for the BGA and then you have to add a flux dispensing station to your pick and place system. Typically, I have only seen that used for flip chip. The risk in any case is that you will have insufficient solder and that will tend to aggravate head and pillow or non-wet opens.


As Jim said, if it is a matter of something with a very tight pitch and you are worried about bridging, that might be it. There is also other ways to approach that. I don’t know, flux only. I know with BGAs and area arrays I always have more of a phobia of getting insufficient volume. To me, flux only unless it is a really good reason, which is not stated the motivation here I would be afraid.


I have just been hearing so much about head and pillow and non-wet open due to the warping of BGA packages and the warping of the substrate that the tendency is to put extra paste there, a higher step up stencil to put higher heights of paste at the corners of your BGAs. Larger apertures to get more paste at the corners and so forth. The idea of not having any paste and going to flux seems to be counterproductive to try to minimize those defects.


I assume we will get a bunch of readers writing in about this. Based on the information C.C. sent us, we hope this helps steer C.C. in the right direction. The only thing that I will add to that is regardless of whether you are using flux only or solder paste or anything else, whatever you do please don’t solder like my brother.


And don’t solder like my brother.


BGA voids are a contest between metal content and flux content. Using 100% flux for rework risks the introduction of voids.
Mitchell Holtzer, Alpha Assembly Solutions
We have considered this for use on .25mm Chip Scale BGAs. Using a small device like this can create a significant mismatch to the rest of the board. The ball size can be so small that the print reliability becomes difficult. We used a flux dip process. This is a feeder with a etched nest for flux which operates much like a pad printer. The nest is topped of and squeegeed to provide a thin fixed depth of fresh flux each time. The part is first dipped by the placement machine and then placed on the PCB.
Don Adams, Bose

Submit A Comment

Comments are reviewed prior to posting. You must include your full name to have your comments posted. We will not post your email address.

Your Name

Your Company
Your E-mail

Your Country
Your Comments

Board Talk
Solder Paste Volume for BGA Rework
Reflow For Rigid Flex
Delay Before Cleaning Partial Assemblies
Problems With Starved "J" Lead Joints
Solder Paste Transfer Efficiency - What/Why
Can a CTE Mismatch Cause Reliability Problems?
Going Beyond Your Solder Paste Work Life
Issues Mixing Silicone and Acrylic Conformal Coatings
Ask the Experts
Bottom Terminated Components and Vias
Is Solder Mask Considered an Insulator
Reduce Glare During Assembly
BGA BAll Sheer Testing
Components Jumping Around During Reflow
Floor Life of MSD Parts
QFN Open Solder Joints
Delamination Causing Scrap