No-Microetch Cleaning

Friday

Jan292010

The New No-MicroEtch™ Cleaning Process

The Company, and its Approach

RD Chemical Company was formed in 1980 to supply the process chemical requirements of the Printed Circuit Board Fabrications Industry and Chemical Milling Industry. The cross fertilization of the technologies developed and learned in the two industries has allowed RD Chemical to produce products for both industries that could not have been developed without the profound insights gained by understanding the problems of both industries.

Recently, the lead frame industry has been called on to produce etched Copper lead frames without using a microetch to prepare the surface of the metal for photoresist, in order for the surface of the metal to retain its original smoothness. This was a challenge to the conventional wisdom, which holds that a microetch, both from a cleaning and a surface roughening point of view, was an absolute prerequisite to good photoresist adhesion.

RD Chemical was able to develop a cleaning system that not only did not require a microetch, but provided photoresist adhesion superior to that obtained with a microetch. RD Chemical's new technology proved that if the cleaning was sufficiently thorough, and all soils were removed, it is unnecessary to remove any metal by microetching.

RD Chemical has proven that the use of a microetch is simplistic and expensive, and now completely unnecessary. This NO-MICROETCH™ cleaning technology is now proving itself to be even more functional and effective in the Printed Circuit Board industry than it was in the Chemical Milling industry.

The Cleaning Theory

RD Chemical discovered that a properly formulated alkaline cleaner, used at an appropriate concentration and temperature, followed by a non-metal removing acid cleaner, can make the use of a microetch optional. This approach, therefore, becomes the most cost-effective way to prepare metals for photoresist.

The heart of the system is an alkaline cleaner unlike any alkaline cleaner previously available. This alkaline cleaner has the capacity to remove any and all organic residues, whether or not they are tied up in a metal complex. This capacity is the critical step, because in older cleaner technologies, certain metal organics could not be removed because they are completely insoluble. The RD Chemical alkaline cleaner systems solve this problem by destroying these insoluble organic residues.

What remains on the copper surface after these organic residues are removed are inorganic metal compounds, like oxides, all of which are readily removed by a strong acid, but non-metal removing, cleaner.

From Cleaning Theory to Product Benefits

The RD Chemical NO-MICROETCH™ clean line offers these important benefits:

Dramatically less expensive cleaning
Improvement in yield, due to improved cleaning
Dramatic reduction in quantity of metal being sent to waste treatment

What is the "catch", or downside to this approach? If there is a "catch", it is that the alkaline cleaner must be used at either significantly higher temperatures, or for a significantly longer period of time, than previous cleaner technologies. Alkaline cleaners work more slowly than acid cleaners, however, properly done, alkaline cleaners work more thoroughly than acid cleaners, as long as they are given either additional time and/or temperature to work.

This is why the RD Chemical recommended process lines suggest longer, higher temperature, alkaline cleaner processing steps, and shorter, or non-existent, microetch steps.

The Ultimate Test, and the Results

Whereas the results of the pre-photoresist cleaning tests were excellent, and expected, when one customer wanted to try the NO-MICROETCH™ cleaning system before oxide, we were skeptical. This would be the ultimate test. Oxide requires a surgically clean surface for uniform color and appearance. Oxide appearance will change with any residue, even one that will not interfere with the functionality.

However, when testing in a production mode, it was found, to even our own shock, that the NO-MICROETCH™ clean system produced a superior oxide coating, both in cosmetics and performance (peel strength) than in the previous microetch based process line. The quality of the oxide was changed (as shown by Electron Micrographs run) for the better. Peel strengths increased and were more uniform panel to panel and edge to edge with the NO-MICROETCH™ cleaning system.

In the following table, we have presented our recommended process line. This line is not the only configuration that will work. It is only a recommended configuration. If your line does not fit this configuration, please contact us. We feel that there are compromises available to obtain similar superior results.

No-Microetch™ Innerlayer Cleaning Process
Pre-Photoresist Lamination, or Pre-Oxide

Process Line	Concentration and temperature	Time	Heater	Process Equipment	Exhaust

1. Alkaline Clean:
Spray application MicroClean CuL (RD-19)	20-30% by volume 120º-150º F (50º-70º C)	1-2 Min. preferred	SS-OK Teflon-OK Titanium-OK Quartz-OK	SS-OK PVC-OK PP-OK	Yes
OR
Immersion (Soak) MicroClean CuLX (RD-68)	20-30% by volume 120º-160º F (50º-75º C)	2+ minutes preferred	See above	See above	No

2. Cold Rinses, cascade preferred. Can probably be sent to drain with only pH adjustment.

3. Acid Clean:
Spray Clean MicroClean S (RD-17)	15% by volume 70º-80º F (20º-25º C)	30-60 seconds	Teflon-OK Titanium-OK Quartz-OK	PVC-OK PE-OK PP-OK	Yes - spray No - soak
OR
Immersion (Soak) MicroClean ZE (RD-10)	15% by volume 70º-80º F (20º-30º C)	30-60 seconds	Teflon-OK Titanium-OK Quartz-OK	PVC-OK PE-OK PP-OK SS-NO

4. Cold Rinses, Cascade preferred (may need to be treated for Copper removal).

Cleaners

Alkaline			Microetch
	MicroClean CuL For spray applications. MicroClean CuL sets new standards for the performance of alkaline cleaners. It is the heart of the RD Chemical innerlayer preparation system.	RD-19		Unietch Powerful, long lived, cost effective persulfate based. Easy to waste treat.	RD-84
	MicroClean CuLX Immersion version of MicroClean CuL.	RD-68		SatinEtch Microetch with built-in anti-tarnish.	RD-83
	FlexClean DM For flex circuits. Organic substrate attack inhibitor allows complete cleaning without damage to the substrates.	RD-11
	HASL PreCleaner SL Alkaline cleaner for cleaning prior to HAL or other final finishes. Will not attack soldermask.	RD-08

Acid			MicroClean
	MicroClean S Spray or Immersion. Powerful cleaner with anti-tarnish, second step in innerlayer clean line.	RD-11		MicroClean™ EC-1 Acid Copper Cleaner/Oxide and Chromate Remover.	RDZ-1603
	CircuitPrep Pre-plate cleaner for Copper. Free rinsing. Will not poison plating bath.	RD-81		MicroClean™ EC-2 Acid Copper Spray Cleaner.	RDZ-1604
	MicroClean ZE Soak or spray. Agressive cleaner. Replaces MicroEtch before Oxide.	RD-10		MicroClean™ EC-3 An Alkaline Spray Cleaner for cleaning Copper Foils.	RDZ-1605
				MicroClean™ EC-4 Acid Copper Cleaner/Oxide and Chromate Remover.	RDZ-1606

Copyright © 2005 RD Chemical Company. TerClean, ChemBond, ChemPosit, ChemStrip, Circuit Prep, FlexClean, HASL PreCleaner SL, MaskStrip, MicroClean, Paladin, PreLam, ResiStrip, SatinEtch, TinPlate, Unietch are trademarks of RD Chemical Company in the US and other countries.