[log in to unmask] wrote: > > I am sending this question again, soon after I sent the question, I lost > contact with the forum and have just now signed back on. Still looking for > an answer: > > Question: Our company processes circuit boards in panel form, (eg. six > three inch square boards forming a panel that will be six inches wide by > nine inches long.) The individual circuit boards are joined to each other > with small webs, 0.25"long by 0.060" wide, separated by two to three inch > spaces. A shear is used to separate the individual boards from the panel > after the wave solder operation. Most of our products have been Type III > assemblies, CEM1 board material, but we have also been doing Type II > assemblies, FR4 board material for the past year. Our problem is that the > larger, multi board FR4 panels(0.060" thick) are bowing during the reflow > process across the width of the panel by as much as 1/4". The bow creates > problems in the next operations of thru-hole insertion or SMT placement. > The bowing appears to be compounded by the panels while they are in a > magazine. I feel that this is due primarily to the practice of using the > webs to connect the circuit boards within the panel. However, if the > amount of web material is increased, we will have to switch from shearing > to a routing process, scored panels or punch/return style boards(I hear > that these warp also!). Another option is a pallet, but this will affect > the flow-thru process, non-value added labor, and increases tooling cost > (we are a high volume shop). Is there another method to eliminate the warp > problem, or will FR4 material always warp in the reflow process, if so by > how much? Is there a panel width, with or without webs that the material > will not warp? I am presently planning to purchase a new reflow oven, and > a center board support is another option. I am using a standard reflow > profile with standard soak zone temperatures, liquidous temperatures, and > peak temperatures. > > *************************************************************************** > * TechNet mail list is provided as a service by IPC using SmartList v3.05 * > *************************************************************************** > * To unsubscribe from this list at any time, send a message to: * > * [log in to unmask] with <subject: unsubscribe> and no text. * > *************************************************************************** Have you tried using clip on 'Board Stiffener' during wave solder process? First you may try leading edge stiffener, add a trailing edge and then on sides to see what helps most. -- Pratap Singh Tel./Fax: 512-255-6820 e-mail: [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************