|Ask the Experts|
September 23, 2020
Overlap Solder Joint Failures
We need to make many thousands of these connections each month. Currentlythis process is being done by hand and we are having cold solder joint failures. Can you suggest an automated way to make this solder joint connection?
|Expert Panel Responses|
Not knowing much about your process and end product; the joint between strips could be flexing thus generating a solder fracture. Consider strip-to-strip connectors. They come in different sizes and they securely hold and connect several LED strips without the need of soldering.
Senior Manufacturing Engineer
This is a common issue picked up by multiple manufactures which are into L.E.D lighting. The most reliable way to overcome this issue is to make use of Through-hole technology, and connect the two strips using link wire.
The befits are as follows:
To answer you second part of your question, Automated soldering does exist, I have used this company before for automatic soldering of a harness to a PCB. They are able to meet a requirement of 3 seconds per joint.
Process Engineering Manager - Electronics
Altech UEC, South Africa
The description of "cold" solder joints is not conclusive as to root cause, however that should not prevent us from envisioning a semi-automated process for soldering the connections that should hopefully eliminate the condition.
I do have a suspicion as to the root cause of the "cold" joints, which is relative movement of the two flex ends during cooling. Here is what I'd envision for automation:
For automated assembly, an investment in fixturing would be needed to hold multiple sets of the 2 strips during heating
A flux-coated preform is another option to solder paste where the preform comes in tape & reel and can be placed. The advantage is that the preform is 100% solder (as opposed to paste that is 50%flux by volume) and would not be prone to spatter.
Comparable in speed to dispensing. Much slower than printing
Technical Manager - Europe
This is a tough one since there are so many variables we do not know from this statement. We would need much more detail to properly reply.
If J.M. would like to send us some samples and provide us with more details,such as current solder used, flex melting point, pad size, distance between pads, etc: we would be happy to try and find a viable solution for them using our Hot Iron soldering robots with a variety of solders.
President and CEO
In looking at your application for soldering two 8mm flex circuits, outsourcing this process immediately comes to mind. I would recommend you contact Analog Technologies Corp. www.analog-tech.com
The reason I recommend them is because Analog has developed their own custom-built laser soldering machines designed just for this application and are experts in this area. They know how to do this type of high-volume processing using their laser soldering machines and specialized solder pre-forms with a special type of oxygen evacuation chemical that when activated remains on the pads for the entire solder cycle and produces pristine solder joints with no spattering of solder balls or solder fines (it is not a "flux" in that sense of the word).
The lasers are completely programmable, not only the power and duration are programmed and are variable, but the spot size and ability of the spot to change size, power, AND travel during a pulse are also programmable as well as the angle of the laser, and as such they can develop a perfect laser profile that will precisely pulse from a pre-heat stage and then lase the area to be soldered so you have a perfect intermetallic formation where the solder melts from the inside out, but ONLY that very precise area is heated.
While you could theoretically develop a soldering process yourself using lasers already available on the market or some other technology such as hot bar soldering or directed convection heat, the time and cost involved in this undertaking does not make it a feasible solution.
Customized laser soldering eliminates the delamination and flux entrapment issues so often seen when trying to solder flex circuits with those other methods, but you have to understand the types of solders, fluxes or anti-oxidation compounds, and many other issues (for example, attempting to laser solder with solder paste is definitely not recommended).
I would contact Bill Berg or Joshua Muonio at Analog (952)894-9228. I am sure they can help you bring your product to market much faster with less cost, both up front and thereafter. I would leverage their equipment already in place and qualified, and their expertise, experience, and knowledge of flex soldering and materials including the various types of flex circuit materials. They have performed very well for other clients that I work for.
I would evaluate using solder preforms and hot bar soldering or IR heating.
President/Senior Technical Consultant
I can back up Mr. Stadem's comment. ATC (Analog Tech. Corp.) is a really good group to challenge with something like this. They have met (and exceeded) our needs every time.Tim Griebel, Starkey Hearing Technologies
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