|Standard solder tip (left) and black chrome solder tip. |
PROMATION, Inc. provides PCB handling solutions and robotic soldering systems to the electronics manufacturing sector. Mr. Goldberg would like to thank Francisco Fourcade, (FOURCAD Inc.) who is a Master IPC Certified Instructor and Michael Goldberg (PROMATION) for their participation in this study.
This study hopes to provide insight and our observations on Black Chrome Tips when using them with table top soldering robots. Black chrome (chromium) plating consists of chrome that turns black after the addition of a contaminant, according to National Metal Finishing.
Back in 1953 a hard, bright chromium-base electro deposit was developed that can be applied at a high rate of deposition. The electrolyte contains chromic acid and nickel chloride plus a carboxylic acid. When this bright deposit is treated with hydrochloric acid (for a few seconds) a black finish results. This finish is non-smudging, very adherent and uniform. These deposits will withstand heating in high vacuum to temperatures of more than 930°F (500°C) and can be applied to most metals without the use of special equipment.
Plated Solder Tips
A typical soldering tip consists of a solid copper core, a plated layer of iron, a plate of nickel behind the working surface and a plated chrome layer. Black chrome attaches best to nickel, which adheres best to copper; however, the key working layer and the one that affects tip life the most is the layer of iron. The working surface of the tip must wet in order to transfer molten solder to the joint and aid in heat transfer. And while copper is actually better for soldering, it is also highly susceptible to being dissolved rapidly by solder alloys. Therefore, iron is most widely used.
In order to make this study, PROMATION developed some black chrome tips and used these tips in a side-by-side test comparison with the company’s standard tip technology. The soldering test was performed using SAC305 solder (no-clean) with a 3.2 percent flux core, sample PCBs with a 1.7mm pad with multi-pin connectors with 0.8mm pins and a PROMATION hot iron soldering robot.
|Test PCB after soldering. |
The tips selected were a 2.4mm half V configuration, one with standard plating and one with black chrome plating. For the purpose of this study, the soldering temperature was set to 375°C.
Each of the test boards consisted of 420 through-hole soldering joints (pin connectors). Tip cleaning was done after 105 joints were soldered, simulating a high-volume production environment using an air/wet sponge combo cleaner.
At first glance, both tips seemed to perform equally well, but through extensive testing — which consisted of recreating a production-like high-volume environment — we observed a slight advantage in quality when using the black chrome tip. The standard tip showed more signs of oxidation and was prone to burnt flux residue buildup on the tip and shaft. Over time, it resulted in a minor decline of soldering operations even when tip maintenance was properly addressed.
By contrast, the black chrome tip demonstrated proficiency in maintaining higher quality soldering throughout the entire test, achieving a superior Class 3 type soldering connection. The complete assembly and inspection processes involved in this study were performed in accordance with IPC J-STD001-E.
In addition, we observed the black chrome tip demonstrated an improved ability to localize the dispensed solder, forming target solder fillets throughout the soldering process. Using an automatic solder feeder, we were able to ensure and consistently deliver a set amount of solder to each joint. The plating construction on the black chrome tip’s shaft was seen to have provided an added benefit: the reduction of wetable area on the tip surface naturally directs the solder more towards the joint area, thus reducing the overall migration of solder up the tip.
Black Chrome in Action
Because most of the black chrome tip’s shaft was plated, the solder traveled only to the source side of the board upon contact, increasing the accuracy of the amount of solder being dispensed into every solder joint. In addition, the activated flux did not accumulate as much on the black chrome tip, since the solder was only allowed to localize at the end of the tip. As a result, smaller amounts of activated flux were left behind.
Localization of solder on the surface of the tip for robotic soldering is key to achieving repeatability and quality work. Totaling all variables and defects (for both the standard tip and black chrome tips), the black chrome tip resulted in a lower defect rate (2.67 percent improvement) in accordance with IPC J-STD001-E. Based upon the accumulated test results, summarized by Master IPC Certified Instructor Francisco Fourcade of FOURCADE, Inc., both tips soldered well; the black chrome tip showed a slight advantage in reduction of overall defects throughout multiple test runs.
Contact: PROMATION, Inc., 9522 58th Place, Kenosha, WI 53144 262- 764-4832 fax: 262-764-4837 Web: http://www.pro-mation-inc.com