Rainbow CL 21 machine

CL21 Hybrid Coating Laminator

The next generation of super etch and plating resist for 2020

By Rainbow Automation (RA)

The arrival of the Rainbow liquid resist and coating system neatly answers issues which challenged traditional wet resists allowing dry film to dominate the resist market for nearly 50 years.  With the Rainbow system, both the chemistry and the coating method are novel and both bring ease of handling and control of coating thicknesses into the hands of the PCB manufacturer.  Unlike dry film, liquid resist flows easily and conforms closely to the surface topography of the substrate.  It can be applied at a thickness defined by the end user which offers both performance and cost saving benefits.  The Rainbow resist is applied at ambient temperature and does not require drying before it is imaged.  This means that the resist is still ‘wet’ at the imaging step.  The panel can still be handled as the resist coating is protected by a layer of Mylar. The resist is first applied to a reel of polyester and then laminated directly onto the copper panel, to leave the protective carrier polyester in place over the resist-transfer coating; in appearance looking almost exactly like a dry film coated panel.   After lamination the panel is ‘singulated’ separating it from the carrier web.  The singulated panel can then be exposed by any method, including DI/LDI.

Pre clean before lamination with liquid resist

The equipment to achieve this is competitive in price with a dry film laminator and rather less complex mechanically & Coating is by a proprietary process and registration is controlled electronically in a single or double-sided application of resist.

Coating thicknesses and /or part numbers can be changed in 2-3 mins.

Imaging can be achieved simultaneously with coating (an option) only requiring UV to cure the image before etching (additive process).  Line widths down to <20 microns can be achieved; the printed image being transferred to either a sheet or another web (e.g. for flexible circuits).  Fully coated panels can be imaged conventionally with a lithographic process or by Laser Direct Imaging. As a typical Rainbow coating can be 6 microns or less, fine line widths are easily achievable and dependent on the resolution of the printer being used.   The chemistry used for developing (more a wash off of the wet ink) and stripping are both industry standards. (0.7% potassium hydroxide @ 35C; 5% sodium hydroxide @ 50C) 

Regarding exposure the Rainbow resists require very low energy levels (as little as 3mJ/ cm2).  Resist reactivity can be matched to the wavelength frequencies of the exposure unit thus obtaining the optimum exposure time in the imaging device to maximise production output.  Operating speed for the coating laminating process is 3-5m/min, greater for coating reel to reel (R2R) and also to create imaged circuit patterns ready for to etch.

Features and benefits of the Rainbow Process

  • User controls coating thickness from 2-30 microns. Thinner resist allows fine line printing, easier developing and etching, and saves cost.
  • Resist conforms readily and coats dendrite structure and most abrasions with excellent adhesion. Reduces open circuits.
  • User controls thickness of protective mylar depending online widths. 
  • Transfer coating system allows sheets or webs to be coated/imaged.
  • Contact cleaning for all materials 
  • Coating and lamination in self-contained clean environment with HEPA filter.  Easy access for servicing.  
  • Coating area and or image changes in 2-3mins. 
  • Coating speed 3-5m/ min
  • Resist is applied at ambient temperature so no thermal shock to substrate.  No pre heat required, no heated rollers required.  
  • Resist is liquid comprised of 100% solids-I.e. no solvent-does not require drying. Resist does not dry out between shifts. Suitable for short or long runs
  • No VOC’s
  • Easy development using standard chemistry as unexposed resist still liquid -retains fine line images.
  • No dwell time required so can be printed immediately after coating.
  • Imaging by direct printing, lithographic or LDI/DI.  Low exposure energy for faster production
  • Resist can be used as etch resist or as a plating resist. Resist fully crosslinked so does not foam in plating baths
  • Tenting capability comparable to dry film
  • Coating technology can be adapted for coating other liquids on other substrates.


Features and benefits of the Rainbow Process Transfer coating lamination
Semi Additive with RTS resist And Coating system Layout side view

Semi Additive with RTS resist And Coating system

The proprietary coating system and resist from Rainbow allows manufacturers new freedoms to create high package density circuitry-fine lines with ultra thin layers.   RTS resist can be used both as an etch resist and a pattern plating resist.  Using a combination of electroless copper, electrolytic copper, etch resist  and standard solder masks layers can be built sequentially.  This method avoids the need for lay up/bonding press, and drilling.  Cost reductions are significant based on having 30% fewer processes.  Additionally, 3D features can be created around the circuitry and the starting point can be a rigidiser-not necessarily copper laminate. Each layer can be as thin as 10 microns (conductive and insulating combined) so a ten layer assembly might only be 100 microns thick.   Registration is achieved by a simple jig system.  Imaging is achieved by a combination of UV printing (lithographic or DI) and Laser ablation which defines the minimum sizes of features that can be obtained.   Via holes less than 1.00mm easily achievable. The process could be automated as required and lends itself to flexible and rigid assemblies/printed electronics.


The market potential for this new approach to PCB resists is clearly significant and growing


The chemistry of the Rainbow resist is established and proven. The method of coating and or imaging is well established. This new (transfer coating) approach can be configured to coat panels, webs, single or double sided as both an etch or plating resist the coating equipment can be in several configurations. Rainbow’s coating and laminating process can also be used for applying other inks or liquids requiring close coating control or imaging.

Rainbow Automation invite interested parties (end users or potential licensees) to contact.  [email protected]

The market potential for this new approach to PCB resists is clearly significant and growing Panel fully coated with resist ready for imaging or printed image ready for etching

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