SMT007 Magazine

SMT007-Aug2019

Issue link: http://iconnect007.uberflip.com/i/1150604

Contents of this Issue

Navigation

Page 67 of 109

68 SMT007 MAGAZINE I AUGUST 2019 in the field they must be properly protected, which typically requires the use of conformal coating. Polyurethane conformal coating is commonly used throughout the industry, but typically, it is used in lower volume produc- tion. Tin whisker mitigation is one of the most common reasons to use a low-outgassing poly- urethane material. Adapting to increases in production can be difficult. An increase in customer demand from 3,000 to 60,000 units per year can cre- ate many challenges in a manufacturing envi- ronment. Currently, a low-outgassing polyure- thane material is applied to the circuit card assemblies via manually spraying using an atomizing handheld air gun. With any man- ual process, there is significant variation in the outcome due to many variables involved; therefore, the process is difficult to control. This variation may be acceptable in low vol- ume production, but for mass production, this method is unsustainable and unreliable. Auto- mating the process is the best way to achieve zero defects, eliminate variation, and accom- modate the strict production schedule. To develop an automated-spraying process for this polyurethane material, there were many factors that had to be taken into con- sideration and many variables that required process controls (Figure 1). There are J-STD- 001 requirements that must be met; polyure- thane conformal coating must be 0.03–0.13 mm (0.001–0.005 in.) [1] . No defects per IPC- A-610 (Acceptability of Electronic Assemblies) are acceptable. There is also the need to meet the customer and drawing requirements. Addi- tionally, strict material requirements, such as pot life and cure time, needed to be consid- ered. All of these factors played a major role in automating the manual hand-spray pro- cess, and it was necessary to understand all of the material requirements and restrictions, customer requirements, and IPC requirements before beginning the evaluation of equipment and development of the process. The entire conformal coating process was evaluated during this experiment, which includes more than just the spraying of poly- urethane material onto the circuit cards. The first step of the process is the preparation of Figure 1: Important considerations for the final process.

Articles in this issue

Archives of this issue

view archives of SMT007 Magazine - SMT007-Aug2019