leadfree-无铅焊接规范.doc

Lead-Free FR-4 Specs: Facts and Fiction By Douglas J. Sober Wednesday, 28 June 2006 Just in time for July 1, what you need to know about IPC-4101B - what it does and what it doesnt do. Not since the 1997 cancellation of MIL-S-13949H has the electronics industry been in such a fervor about a base material specification. Remember the proclamations? No MIL-SPEC! No QPL! IPC-4101 is the replacement! Planes will fall from the sky and mankind will cease to exist! However, the predicted apocalypse did not take place. IPC-4101 became the base materials standard for the U.S. and much of the world as well. IPC-4101 and its subsequent revision, IPC-4101A, represent one of the most widely used IPC documents. But whereas the A revision was written and implemented as an evolutionary sequel to the original, IPC-4101B has become a lightning rod for attention. The proposed B revision of IPC-4101, Specification for Base Materials for Rigid and Multilayer Printed Boards, contains new specification sheets describing FR-4 base materials that are compatible with lead-free assembly. These specification sheets also outline qualification and periodic conformance requirements not found currently for FR-4 base materials, including Td, T260, T288, T300 and Z-axis expansion. These specification sheets are listed here along with some descriptive information: IPC-4101B/99. High Tg FR-4, inorganic fillers, brominated flame retardant IPC-4101B/101. Low Tg FR-4, inorganic fillers, brominated flame retardant IPC-4101B/121. Low Tg FR-4, no fillers, brominated flame retardant IPC-4101B/124. High Tg FR-4, no fillers, brominated flame retardant IPC-4101B/126. Very high Tg, inorganic fillers, brominated flame retardant IPC-4101B/129. Very high Tg, no fillers, brominated flame retardant Fact: Keywords will be part of the document. IPC-4101B has been expanded significantly in terms of the base material grades covered, especially in the generic family called FR-4. The original 1997 version of IPC-4101 had 30 specification sheets and IPC-4101B now has 55. The organizational structure developed in the 1990s has been overwhelmed by the inclusion of new materials over the past nine years. For example, the 20 series specification numbers (i.e., 20, 21, 22 and so forth) were designated for FR-4 materials. When specification sheet number 29 was reached, FR-4 materials spilled over into the 90 series and then the 100 series numbers. In order to help users more easily find materials suited to their needs, keywords have been developed for each of the 55 specification sheets in IPC-4101B. The intention was to provide the typical composition, application, performance characteristics and market for each base material. In the electronic copies of IPC-4101B, the user will be able to conduct a search for the specification sheets by a specific keyword. For example, typing in the term lead-free FR-4 will list specification sheet numbers 99, 101, 121, 124, 126 and 129. Fiction: Keywords are requirements. Keywords will provide the user with an easy reference as to the normal use of a base material grade. A lot of the angst concerning keywords is that they are perceived to be part of the requirements for each specification sheet number. The keywords are not requirements; they are simply information. Currently each specification sheet also has the following instruction above the keywords section in the header:Keywords: (For Search Only)NOT Grade RequirementsSee Section 7 Fiction: Keywords guarantee performance. The following can be found at the front of each IPC standard: IPC Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with a minimum delay the proper product for his particular need. There is no guarantee of performance. Did materials certified to MIL-S-13949H provide a guarantee of performance of a radar system in an F-16? Many different factors beyond the control of the standard can influence the ability to manufacture a functional board, assembly or electronic part. The best that can be said is that materials certified to an IPC standard, or any other standard for that matter, have the best probability of success. Fiction: Keywords restrict material use. The main message of the keywords is typical use. Typical use does not mean the only use. The keyword single-sided may appear next to CEM-1, but that does not mean it cant be used for double-sided boards with a plated through-hole if someone can do it. It simply means the typical use is single-sided boards. In addition, applications are not limited to the specification sheets with that specific keyword. For example, there are six specification sheets with the keyword lead-free FR-4. Can other FR-4 materials be used for lead-free assembly? Yes. Can base materials other than FR-4 be used for lead-free assembly? Yes. IPC has always endorsed a fitness for use philosophy when it comes to base materials for specific applications. The list of keywords by specification sheet number is shown in Table 1 PDF format. Section 7 of IPC-4101B clearly discusses the intent of these keywords. Several examples have been presented to clarify the use of keywords as intended by the IPC Laminate and Prepreg Subcommittee members who prepared this document. Most of the concerns about IPC-4101B and the use of the keywords are fiction. Suppliers and customers alike must utilize education and communication t