Residues RAT

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The Residues Rat product provides a method for detecting unreacted flux residues on a printed circuit board.

  • Mapping levels of production residues on the PCBA
  • Optimization of the soldering process
  • Quality control of the production process
SKU: Residues-RAT Category:

The Residues Rat comes to a liquid spray, which solidifies into a gel when applied to the surface of a PCB. In this way, complicated, non-planar geometries can be investigated while the process residues are fixed to their original site with no smearing.

The Residues Rat gel is designed, so that a color change occurs if unreacted flux residues are present on the surface. In this way, your soldering process can easily be optimized for the highest possible environmental reliability.

Integrated circuit after manual rework with flux leaving aggressive residues

Integrated circuit after manual rework with flux leaving aggressive residues

After selective wave soldering the temperature at stencil edges is not sufficient to decompose aggressive parts in the flux

After selective wave soldering the temperature at stencil edges is not sufficient to decompose aggressive parts in the flux

1 ESD proven package of Residues Rat test kit includes:

  • 1 bottle of Residues Rat gel
  • 2 trigger sprays
  • Gloves
  • Extra dispensing pins

Please note that microwave oven heating is needed in order for gel to be sprayed. The gel will remain hot (use gloves) and ready to use for at least 30 minutes.

Worldwide shipping up to 5 working days with FEDEX
(local tax/customs may apply).

Price is shown without VAT. When shipping address is given during the ordering/checkout process, VAT will be automatically adjusted. For EU companies: Remember to add your valid company number in order to have the VAT deducted, otherwise Danish VAT will be added.

Can I clean the PCBA after Residues Rat testing?

Generally, we recommend that the Residues Rat test is to be considered a destructive test. However, if done before the gel dries and hardens, the gel can easily be peeled off, and if the board can washed with lukewarm water (preferentially using a soft brush), the process should not leave any residues. However, care should be taken that no gel remains under components, in through holes etc.
EC-RAT ApS is not liable for the PCBA functionality after testing!

How many PCBAs can I test with the kit?

The amount of PCBAs that can be investigated depends on the geometries of the PCBAs and how much you apply, but under normal circumstances the three bottles will cover ~1000 cm2 (ex. ~5 PCBAs measuring 10×20 cm).

Can I use the remaining gel in the bottle after it has cooled down?

Yes, no problem. It can be reheated. But pay attention to the effect of the microwave and heating time, as less volume heats up more quickly! However, sometimes you need to change the spray head, as the solidified gel can block the nozzle when reused.
Don’t put the cap on the bottle before the gel has cooled down to room temperature.

Unreacted solder flux residues from wave and selective soldering processes are directly detectable with the Residues Rat test method. For re-flow solder flux residues, however, the unreacted components are often embedded in the rosin of the flux. It should be noted, that this does not mean that the flux does not contain unreacted components, and if the PCBA is exposed to high humidity during service life, the rosin opens, and unreacted residues can decrease surface insulation resistance. This is commonly observed as “white residues”.

The Residues Rat test can be used on re-flow solder, but before the test is applied, the rosin must be opened by exposure to humidity. This can be done by exposing the PCBA to 100 % RH for approx. 24 hours at room temperature.

Reference re-flow soldered PCB compared with PCB after 48h at 60C/99%RH

Reference re-flow soldered PCB compared with PCB after 48h at 60C/99%RH

Danfoss controls suppliers

As a partner in Celcorr Danfoss has helped to test Residues Rat’s usability out of the industry. According to Kirsten Stentoft-Hansen, Lead Reliability Engineer at Danfoss Power Electronics, Danfoss is very satisfied with the gel. The major advantage of Residues Rat is the ability to quickly test a printed circuit board if a visual inspection gives rise to suspicion of flux residues.

Danfoss already uses Residues RAT to continuous quality check of printed circuit board assembly deliveries from suppliers. The gel is used primarily to demonstrate the need for further studies – laboratory test and purity test, for example – because the gel alone can not demonstrate the types of acid residues if any, is left on the board.

“Residues Rat allows very quick analysis – in hours compared to days with conventional analysis methods, where it is practically impossible to distinguish visually between tin contamination and flux residues.”

Kirsten Stentoft-Hansen about Residues RAT product

The Residues Rat test is easy to do, but some clients prefer that we do the test for them. When ordering this product, you can send up to 5 PCBA’s for analysis.

After receiving the PCBA’s, we will do the residues detection test and send you the results within a maximum of 2 weeks.

EC-RAT will clean the PCBA’s with DI water and a soft brush. After sufficient drying, the PCBA’s will be returned to the shipping address provided in the order.

EC-RAT ApS does not take any responsibility to the functionality of the tested PCBA’s after the Residues Rat test, and will not be held responsible for any lack of functionality of the PCBA’s nor will EC-RAT be held responsible for any likely or unlikely accidents, personal injury, death or any other damage or financial loss suffered, that might be a consequence of malfunction of the tested PCBA’s.

The Residues Rat test PCBA

Low cost and effective

Low cost and easy to use – no expensive equipment required. Fast analysis – visual results are obtained within two minutes.


Selective – the inspection shows where production leaves “hot-spots” having high levels of contamination.


The optimized Residues Rat solution can detect residues having a 1.0 µg/cm2 NaCl equivalent, which is below the 1.56 µg/cm2 given by the IPC-TM-650 standard.


Results show clean, lightly- and heavily contaminated areas. A colour scale is provided, which can be used to transfer a colourimetric observation to an approximate level of surface contamination (converted into a µg/cm2 NaCl equivalent).