In the complex production of printed circuit boards, there are two typical manufacturing processes for the core processes of through-hole plating and structuring. A distinction is made between "pattern plating" and "panel plating". Depending on the requirements, layer structure and layout, KSG decides on the most suitable manufacturing process. A combination of both processes can also be used. ("semi-pattern plating") can be used. Design rules for this can be found at → 8.6 Design Rules | Outer layers/metallized layer.
General: Integration into the production process
What does pattern plating mean?
The term "Pattern plating" means the coating (plating) with a pattern (pattern). It therefore describes the selective electroplating of a production panel that has previously been provided with a photomask. In the photo process, the photomask is applied negatively to the panel in order to selectively build up the conductor pattern in the electroplating process. This is therefore also referred to as LBA or the Ladder diagram structure. The areas covered by the photomask are the areas that will be etched away later. To protect the deposited copper from the subsequent etching process, a thin layer of tin is also applied to the copper. This tin layer serves as an etch resist and has no function for the soldering process. It is removed again after the etching process.
Advantages of pattern plating
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Less copper to be etched and therefore smaller distances possible with comparable conductor thickness than in "panel plating" - Smaller residual rings tend to be feasible than with "panel plating", as the holes do not need to be covered and there is no need for a support surface for the photomask around the hole
- Simple recovery of the etched copper from the alkaline etching process and recycling of the used etching solution
- Fewer restrictions on sizes and shapes of metallized edges
- Production of partially metallized bores without burrs possible after opening the sleeves by milling
XPERTS tip: Save the pattern plating process sequence as download
Challenges
- Layout-related fluctuations in the copper heights across the entire production panel are not significant compared to the "Panelplating" higher (avoiding an inhomogeneous copper distribution over the layout can counteract this - "Copper Balancing")
- Additional process steps required due to the deposition and removal of the technological etch resist layer (electroplated tin)
- The copper layer thickness that can be selectively deposited is, in contrast to the "Panelplating" limited by the height of the photo mask
What is panel plating?
The term "Panelplating" is derived from the production format, the English term "Panel" (cutting/printing) and the copper coating, the English word "Plating" from. In this case, the coating is applied without a photomask, i.e. over the entire surface.
The term "Tenting technique" is used, as in this technology the holes are covered with a photomask (resist film) after electroplating (tent=Tent). In contrast to the "Pattern plating", the photomask is applied positively and all covered areas also correspond to the structures that remain on the panel after the etching process.
Advantages of panelplating
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Very uniform copper height across the entire production panel, as layout effects are only caused by the distribution of the plated-through holes - Precise control of the copper layer possible, e.g. for drill holes with very tight tolerances (e.g. Micro-Press-Fit, a special type of press-fit technology)
- Reduced contamination of the galvanic copper baths with degradation products from the photomasks
- Deposition of a tin layer is not necessary, as the function of the etch resist is taken over by the photomask
- No limitation of the copper layer to be deposited due to the height of the photomask
XPERTS tip: Save the process sequence of the Panelplating as download
Challenges
- Slightly larger and closed residual rings required than for "Pattern plating"
- Not quite as fine a structure as "Pattern plating" possible
- Certain layout elements such as large through-holes, milling or edge metallization cannot always be reliably covered with photo masks
- Structuring is more demanding in comparison, as the entire copper structure must be etched (the greater the copper thickness to be etched, the greater the spacing must be)
- Copper recovery from the acidic etching solutions used here is somewhat more complex compared to the alkaline etching process, as direct electrolysis is not possible
CONCLUSION
The General challenge is to bring the required copper layer thicknesses in the holes in line with the layout to be structured. Despite the further development of systems and processes, a high copper layer thickness in holes with a very small line/space always leads to additional work, which is ultimately reflected in the costs. The layout, i.e. the distribution of copper areas and holes within a circuit, also plays a role in copper deposition that should not be underestimated. Through a targeted "Copper Balancing" The quality of the printed circuit boards can be positively influenced as early as the design phase by the use of circuitry optimization techniques, such as filling in open areas (including areas that are milled away later).
Any questions?
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2 Responses
Informative and easy-to-understand article about pattern plating and panel plating in electronics production, in which the functionality and advantages of both processes are explained in a practical way. In our experience, panel plating is usually the better option, especially for large quantities, as the costs for large production series per unit are reduced.
Very well described and elaborated.