Analysing the molecular fingerprint of your PCB in electronics manufacturing

Author : Viktoria Rawinski | Founder & CEO | Rawinski GmbH

01 July 2022

Molecular fingerprint of PCBs in electronics manufacturing
Molecular fingerprint of PCBs in electronics manufacturing

Rapid growth rates in electronics production, combined with continually rising quality standards & high requirements on process reliability, demand innovative measurement methods in order to remain competitive & guarantee the highest quality standards to customers...

This article was originally featured in the July 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.

Established testing methods, such as optical & electrical tests, can often fail to detect serious quality deviations, such as high moisture content in PCB substrates, thermal damage, insufficient degree of crosslinking or chemical impurities. However, as Viktoria Rawinski, founder & CEO at materials analysis expert, Rawinski GmbH tells us here, these flaws can be detected precisely and reliably by molecular fingerprinting with infrared spectroscopic analysis, or so-called FT-IR analysis…

Fourier-transform infrared (or FT-IR) spectroscopy is a well-established analytical technique that uses the principle of light absorption in the infrared range of the electromagnetic spectrum. Its name originates from the fact that a Fourier transform (a mathematical process) is required to convert the raw data into the actual spectrum. In this process, electromagnetic energy is converted into oscillation energy. This energy is unique for each sample, providing its specific molecular fingerprint, thus allowing clear identification of the material. FT-IR can be used when evaluating manufactured electronic materials, including printed circuit boards (PCBs), to help assure excellent quality, providing reliable deep insights into the molecular structure of the material.

Early detection of quality deviations with FT-IR analyses

The causes of quality problems often can be found in the smallest production deviations, which can easily be overlooked. Insufficient cross-linking of the PCB substrate, for example, only becomes noticeable as PCB warpage after soldering. However, the consequences are serious for the quality and lifetime of the complete board. As a result, internal stresses can lead to delamination, insufficient adhesion of solder pads and, finally, to early board failure. These quality problems are also noticeable in the increased formation of condensate in the soldering machine, because non-crosslinked low-molecular compounds outgas from the PCB and polymerize, crosslink and condense in the soldering process.

Influence of oxygen & humidity in the production process & storage can lead to quality problems
Influence of oxygen & humidity in the production process & storage can lead to quality problems

In the case of solder resist, insufficient crosslinking may result, for example, in diffusion effects, an inconsistent surface and loss of the protective effect. The deviating quality is neither visually, nor electrically noticeable before the soldering process. Often, an insufficiently crosslinked solder resist layer can be only noticed after the cleaning process, when it does not chemically resist to the cleaning medium. Here, too, increased condensate formation of the soldering machine is an indicator of increased outgassing of non-crosslinked low-molecular compounds. The condensate layer can appear as a polymerized and crosslinked layer, as well as in the form of crystalline structures.

Insufficient crosslinking in solder resist can have several causes. Too short a curing time is one of these causes. This results in higher production throughput, but leads to serious quality problems in the subsequent soldering process. Other causes are increased humidity and the influence of oxygen in the manufacturing process. Both can lead to inhibition of polymerization and crosslinking reactions. In this case, only a weakened polymerization and crosslinking reaction can be started by subsequent UV curing. Here, FT-IR analyses allow identification of the quality deviation at the molecular level and thus makes an early process adjustment possible.

In practice, the quality of the finished assembly depends on numerous factors. Strict compliance of defined production requirements in PCB manufacturing is just as much a part of this as the subsequent printing, soldering and cleaning process. The combination of the PCB substrate, solder resist and solder paste is a key factor in the polymerization and crosslinking reactions of the condensate layer in the soldering system. In this way, the subsequent cleaning process of both the assemblies and the soldering system can be optimised, and the cleaning medium can be used in a more resource-efficient way. Effects such as residues on the metallic surfaces of the PCB can also be avoided. This means that they can no longer lead to reduced wettability and solder bead formation in the soldering process.

FT-IR analyses: fast & cost-efficient

FT-IR analyses - fast & cost-effective
FT-IR analyses - fast & cost-effective

FT-IR analyses can be used to identify defects that remain hidden to conventional testing methods. Production and storage defects can be detected in just a few minutes. The analysis results are available to customers digitally immediately after the measurement. FT-IR material analyses can support a resource-saving, smooth production process and help to significantly reduce additional costs, complaints and unnecessary waste.

FT-IR material analyses help to detect quality deviations, such as an insufficient degree of crosslinking or a high degree of humidity in the PCB substrate, in time and to prevent them effectively. If a so-called ‘golden measurement’ of the target quality is available, reference measurements of subsequent batches can be performed quickly and cost-efficiently. For the infrared spectroscopic analyses, even small sample quantities are sufficient. Precise results are available to the customer within a very short time and guarantee compliance with the highest quality standards at the molecular level.

Experience makes the key difference

Rawinski GmbH is your competent, reliable and independent partner. Our specialists will gladly support you from performing the necessary evaluations, choosing the right suppliers to analysing the condensate residues in the soldering systems in order to extend maintenance cycles and effectively minimise cleaning costs. With many years of experience in the fields of electronics manufacturing, thermal processes, infrared spectroscopic analyses and material characterization, we are able to understand your challenges quickly and provide you with optimal support. The result is the assurance of excellent quality in electronics production at the molecular level in order to distinguish from market competitors in the long term.

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