ONLY EMS SCIENCE OF SOLDERING PREVENTS HEAT DAMAGE
"Heat damage from improper use of soldering irons is a serious issue that generally goes unnoticed in today’s electronics manufacturing"
Heat damage from improper use of soldering irons is a serious issue that generally goes unnoticed in today’s electronics manufacturing. By conditioning operators to use soldering irons using a technique designed for connecting wires to lugs of vacuum tube sockets more than 5 decades ago, the most common solder training causes a needlessly high failure rate. Only Electronics Manufacturing Sciences offers the scientific heat control technique that prevents thermal damage.
Why Assemblies Fail
Electronic assemblies fail for four basic reasons related to assembly:
- Mechanical (improper handling)
- Electrical (ESD)
- Chemical (generally conductive residues of excessively acidic fluxes)
- Heat damage during soldering (primarily hand and wave soldering)
Some forms of improper handling are intuitively obvious. Stacking of assemblies at inspection or repair stations is easily recognized as unacceptable. But other forms of abuse attract little attention. For example, "cleaning" PCBs with alcohol and a brush to remove flux residues after repair has undesirable consequences but generally goes unchallenged.
ESD is also well known, largely because the huge market for anti–static materials supports an equally huge advertising budget. The actual failure rate caused by ESD today is small but the attention it receives is great.
Flux–related failures (intermittent and permanent) are common, particularly in high humidity environments, and the phenomenon of dendrites is well known. The only way to prevent these failures is by selecting a safe flux and this non–trivial exercise generally requires help from a company like Electronics Manufacturing Sciences.
Purple plague kills
Heat damage has many forms, many of them invisible. Heat damage like burned laminate and melted component bodies is easy to see. But the damage inside components as a result of hand soldering can't be seen and is more likely to escape detection.
Heat from soldering irons flows up component leads and along the wires connecting leads to the die circuitry, causing elevated temperature where the wire is bonded to the die. The high temperature causes rapid growth of intermetallic between the bond (typically gold) and the circuit (typically alumina). The intermetallic is less conductive than the bond, so switching properties change. Also, the alumina migrates into the ball, creating gaps in the chip circuitry and causing failure. This phenomenon (known as “purple plague” by the component industry because of the Au/Al color) is shown in the photograph below. The temperature responsible for the failure was only 235°C, far below the lowest operating temperature of any soldering iron.
The heat damage inside components can range from inconsequential (reduced life span but beyond the expected use of the assembly) to grave (failure at test or, much worse, infant mortality when the assembly reaches the customer).
What happened to heat sinks?
Concern about heat damage to components during manual soldering ran high in the early days of solid state circuits. Operators were instructed to attach metal alligator clamps to the lead next to the component body; as heat flowed up the lead, it would be absorbed by the clamp (a “heat sink”) rather than progressing into the component. As components grew smaller, however, there was no room for the heat sinks and operators were simply told to “solder faster.” That doesn’t seem very reliable to us, so we developed our own technique that absolutely prevents heat damage. Our technique does not require special equipment (it works perfectly well even with the most inexpensive soldering irons, allowing users to save money on tools). It takes no longer than the traditional soldering technique. In fact, the only differences between our technique and the traditional approach are (1) it prevents heat damage and (2) it saves money on tools, calibration of irons and better reliability.
Heat damage from wave soldering
Manual soldering, being less controlled, poses the most serious risk of heat damage. However, wave soldering causes heat damage, too. Sagging of the laminate as the assembly passes over the solder reflects melting of the glass fibers (which, in turn, compromises the insulating properties of the laminate). Larger chip components delaminate (crack) when subjected to excessive heat. These degradations occur in the temperature range at which most plants set their solder baths.
EMS clients avoid heat damage during soldering. Scientific heat control in hand soldering is taught only in EMS Science of Soldering (including The Recipe). Our wave soldering process guidelines prevent heat damage, too. We would like to explain why we can help you eliminate heat damage, too. Just write or call (01)727–866-6502, extension 21 for more information.
