ECD Thermal Profile - White Paper

This article examines application and verification techniques for flux deposition through spray fluxing in wave soldering processes, focusing on through-hole penetration and coverage uniformity. The work evaluates simple methods of spray fluxing verification processes to prevent solder defects and improve product quality.

Classic printed circuit board (PCB) profiling involves connecting thermocouples from your PCB assembly to a data recording profiling instrument and running the assembly through your reflow oven. Profiling has two primary objectives: 1) determining the correct process settings for a given PCB assembly and 2) verifying process consistency to ensure repeatable results. By viewing the actual temperatures (thermal profile) of a PCB while it travels through the reflow oven, once can verify and/or correct oven settings to achieve optimum quality for the finished product.

Reflow soldering is a thermal process which is designed to melt a solder paste (a mixture of solder alloy powder with a solder flux to form a tacky paste) which has been placed on the exposed conductive pads of a circuit board and the contacts or leads of an electronic device to form a solder joint.

This paper presents the results of an initial evaluation study to determine if a printed circuit board’s (PCB’s) profile can be verified by using only 3 thermocouples (T/Cs). Herein, this paper describes two processes: a “characterization” process and a “verification” process.

Thermal profiling is always necessary — no matter what. Or is it? If this sounds like a contradiction, there are currently ways of profiling that provide alternatives to the most time-consuming or labor-intensive methods. For example, oven verification may in some cases replace repeated board profiles, but only if strict parameters are met. The trick is in knowing when to profile the board or verify the oven performance.

Thermal Profiling is a recognized necessity. As mid-to-high volume production continues to dominate in many areas, it is beneficial to understand the available choices in profiling, and which ones will work best under what circumstances. One of the main distinctions to be made is between board profiling and oven profiling. Having said that, it must be clear as to exactly when it is possible to effectively replace board profiling with oven profiling, the benefits of doing so, and the parameters that are required for successful implementation.

There is no doubt that in today’s more sophisticated electronics market, with boards populated with everything from BGAs to SiPs (System in Package), process control is more important than ever. At the center of achieving that control, you will find thermal management. And since thermal management cannot be achieved, or documented, without thermal profiling, thermal profiling brings us to the heart of the matter.

After BGA removal for repair, there typically is an excess of solder remaining on the board side, which can cause short circuits by bridging between adjacent joints and/or open circuits by preventing the complete collapse of all joints. It is imperative that the excess solder be removed to present a uniform surface across the site for proper component attachment, as BGA rework can be both time consuming and costly.

Thermal profiling is a critical function in printed circuit board assembly. This article describes thermal profiling hardware and process management software solutions as used at EMS provider Axiom Electronics LLC to meet the thermal profiling challenges of today’s microelectronics environment. Reflow challenges include thermal inequalities of high layer count circuit boards that have uneven mass distribution, components of varying sizes, micro BGAs, high ball-count BGAs, LGAs, etc. These easy to use thermal profiling tools help to improve yields by providing a stable repeatable process while saving time and providing necessary supporting documentation.

As the electronics industry prepares for the possibility of Pb-free Printed Circuit Board Assembly (PCBA) processing without the