Solder Alloys?How to Select the Best Option for Your PCB Assembly

Posted by Alphaassembly on August 29th, 2017

Not all solders are created equal. Each alloy type has a specific temperature specification and is suited to a specific set of applications. Choosing the right solder alloy can make or break your PCB assembly, affecting the reliability, accuracy and performance of the circuit board being manufactured as well as the cost effectiveness of your overall operations. Therefore, as a PCB manufacturer, it is important that you carefully analyze different solder alloys and select the one that perfectly fits your requirements. To help you with the selection, here is a guide that talks about all the factors that you must keep in mind:

Lead Content
The RoHS and WEEE directives have now made it mandatory to avoid using lead-based solder pastes and alloys to prevent the environment toxicity and health hazards. The industry is still moving slowly towards becoming completely lead-free, mainly because most lead-free solders available right now melt at higher temperatures, require higher temperature flux and provide more brittle joints. You will therefore, first have to ensure that you steer clear of lead-based alternatives and select a lead-free solder alloy that can feasibly work with your operations.

Melting Temperature
At temperatures below solidus, the alloy will retain a completely solid state. Temperatures above liquidus will cause the alloy to become completely liquid. The temperature range between these two extremes is when the alloy attains a viscous, plastic like state and quality that is desirable for PCB soldering applications. This is the state where the solder is applied to the substrate in the form of a paste so that it can hold electrical connections and components firmly in place and create strong bonds between surfaces. The liquidus and solidus temperature ranges of your chosen alloy should therefore be workable with the materials and quality of components and boards being used in your PCB assembly.

Alloy powder particle size
Most solder pastes are basically comprised of metal alloy fillers that are suspended in a thick medium known as flux. The actual size of these dispersed alloy particles can play a critical role in the outcome, efficiency and economy of your operations. If the particles are too large, it will lead to printing difficulties and paste dispensing hassles. Particles that are too small will be a bigger cost for your operations overall. Your selection of solder alloy should therefore be dependent on the powder particle size that its paste formulations are available in.

Solder Joint attributes
The last and final factor to keep in mind is the solder joint you are aiming to create with the particular alloy. Tensile strength, thermal fatigue resistance, vibration withstanding qualities, electrical conductivity levels and resistance to stress cracking and mechanical shocks – all these are factors that will affect the quality and strength of the solder bond that will be created using the alloy.

Once you have considered the above listed factors and found suitable alternatives, you can move on towards comparing the most suitable solder alloy type for your PCB assembly operations.

About the Author:

Alpha Assembly Solutions, Inc. is the global leader in the development, manufacturing and sales of innovative specialty materials used in a wide range of industry segments, including electronics assembly, power electronics, die attach, LED lighting, photovoltaics, semiconductor packaging, automotive and others. Since its founding in 1872, Alpha has been committed to developing and manufacturing the highest quality specialty materials.