|Ask the Experts|
March 11, 2020
Syringe Dispensed Solder Paste for Hand Soldering
You recently had a discussion about the application of liquid flux for hand soldering operations. Would you advise using a syringe to dispense solder paste as an alternative to dispensing flux only? If use of solder paste dispensed from a syringe was acceptable, what expiration would you apply to these syringes?
|Expert Panel Responses|
Solder pastes in syringes have lower viscosities and usually lower metal content 80-85% compared to printable solder pastes which have 90+%, separation is normally the issue. The shelf life is less than liquid fluxes which have a 1 year shelf life or more; solder pastes in syringes tend to be anywhere from 3 months to 6 months and require refrigeration at 10 Centigrade.
The usual issues with syringe dispensing are separation of flux and metal in the syringe and/or needle blockage.
For liquid flux applying flux in excess, is the issue. So both have advantages and disadvantages in use.
Senior Market Development Engineer
I would only use a syringe to dispense solder paste in applications where the volume of paste was not critical, such as attachment of a metallic EMI shield. For component leads, never. Solder paste for component mounting needs to be tightly controlled, either by stencil printing or by jetting.
In terms of expiration, that depends a great deal on the paste chemistry. If you get the syringe tubes from the paste manufacturer pre-loaded, then use the given expiration date. If you are loading syringes yourself, work with your vendor to determine how long a working life you have depending on how you fill the syringes.
Principal Materials and Process Engineer
Syringe-dispensed solder paste can be an acceptable substitute for wire + liquid flux; some pastes work better than others for this application. Many solder paste manufacturers sell "dispense grade" pastes that have lower viscosity than pastes intended for stencil printing.
If you are not buying in the syringes but re-packaging from tubes, the shelf-life of properly filled and stored syringes should be the same as for the original packaging. Best practice is to label the re-packaged syringes with the material, lot and date of expiry information from the original container.
The key to success with this process is controlling your dispensing operation and ensuring that the flux is completely reacted. Hot air tools can be a good match for dispensed solder paste; some pastes react badly to heating with an iron. Discuss your intended soldering process with the solder paste manufacturer for guidance on paste selection and process optimization.
Using syringe packed solder paste is a very common application for SMT rework. Some of the key things to control in your facility:
Regional Sales Manager
OK International Inc.
Dispensing solder paste can be a science in itself and in my opinion best to stay away from. When dispensing solder paste the nozzle inside diameter (ID) size becomes a big factor. If the nozzle is too small, the solder will separate in the nozzle, so it is important to understand the relationship between particle sizeof the solder paste and Nozzle dimensions.
Many solder company's sale solder paste specifically designed for dispensing, so if this is something you plan to follow up, you should make sure that your vendor understands that you will be dispensing the material when discussing solder paste selection.
Dispensing grade solder paste will have higher flux content than standard solder paste, this is by design to help lubricate the nozzle or dilute the number of solder particles being forced out the nozzle at any given time,reducing the number of opportunities to clog the nozzle.
Consult your vendor for recommendations on shelf life for dispensing grade solder, typical solder paste shelf life is around 6 months, however left at room temperature, the metal in the solder paste will start to separate, so it is best practice to dispose of unused material after a couple of days usage.
|Submit A Comment|
Free Newsletter Subscription
Circuitnet is built for professionals who bear the responsibility of looking ahead, imagining the future, and preparing for it.
Insert Your Email Address