Alain, I talked to Floyd Gentry, current Chairman of the IPC-A-600 and Arny Andrade who was the chairman of the A-600E. You can email Arny if you would like mor information on the tests performed by Sandia. His address is [log in to unmask] Their replies are as follows: ------------------------------------- Multilayer boards without etchback exhibit higher electrical resistance during thermal shock and cycling. This has been substantiated by controlled environmental testing conducted here at Sandia National Laboratories on boards specifically designed for this purpose. It's not stated whether these boards are epoxy or polyimide construction. Polyimides which are typically used for high temperature applications can generally be fabricated with only a smear removal process due to their higher glass transition temperature (Tg) which results in less thermal expansion. However, drill smear can occur in any of these materials which must be removed before plating. Consequently, I would personally insist on at least a smear removal process at the very minimum. I would also question the validity of the 10-15% cost savings. If a smear removal is substituted for deep etchback, a shorter cycle might be possible and glass etch might be eliminated. However, I feel that a small reduction in cycle time would not justify a potential reduction in long term reliability. I would recommend that either a etchback or smear removal be continued depending upon the material construction and/or application requirements. I don't know of any reputable fabricator who couldn't accommodate one of these requirements in a cost effective manor. Floyd Gentry Sandia National Labs __________________________________________________ Etchback enhances the innerlayer interconnects. One ounce inner layers measure approximately 1.1 to 1.3 mils in thickness but with 1-mil of etchback the contact area increases to 3.1 to 3.3 mils establishing a "c" type interconnect. Inner layer connections are stressed during assembly soldering operations and can result in interconnection cracks and/or opens but filled with solder. This connection can result in latent interconnection failure. Automotive environments are very severe and should be designed to high-rel requirements. Lab tests at Sandia verified the need of etchback. Test PWBs with both chemically cleaned and etchback interconnections were fabricated. Thermal cycles at 500F were performed using hot oil and IR as the heat medium. Resistance measurements were taken after each cycle. Results: Chemically cleaned interconnects increased resistance ending in open circuits. Etchback interconnects maintained their initial resistance. 40-cycles were performed with each heat medium with the same results. Therefore 10% to 15% savings may be false economy. Arny Andrade Sandia National Labs **************************************************** Jon Holmen Technical Project Manager IPC 2215 Sanders Road Northbrook IL 60062-6135 Phone (708) 509-9700 ex329 Fax (708) 509-9798 e-mail [log in to unmask] ***************************************************** On Tue, 21 Nov 1995, Fouquet, Alain wrote: > > To all, > > In an effort to reduce cost, our boards manufacturers are proposing to > remove the requirements for etchback. This is reported to be a saving of > 10-15% of the bare board. For an equipment subject to be used in an > environment which may be similar to a car and possibly marine types, > questions are: > > 1- Do we put ourselves in a position where reliability will drop > significantly if etchback is not specified? > > 2- Is etchback normally used in the automotive industry for multi-layer > board if used? If not what alternative to use? > > 3- Is the 10-15% cost reduction realistic? > > 4- General consumables like computers, are they using this process? > > > Any other comments would be appreciated. > > > Alain Fouquet > Canadian Marconi Company > Ville Saint-Laurent, QC, Canada > email: [log in to unmask] > >