Dennis, If the base laminate is made of a high Tg laminate then the "Z" expansion (PPM) is less likely to exhibit the type of failures as you mentioned. High Tg laminates are more favorable for products that have multiple thermal excursions. (i.e., two or three assembly thermal excursions like wave, IR, FTIR, Hot Bar or forced air) Another thing that that is critical is the elongation and tensile strength of the plated copper in the hole. Of course ample (correct) copper plating thickness is essential. High Aspect Ratio plating has a tendency to produce a "dog boning" appearance that could have a less than desired thickness in the center and too much at the knees. These types of deposits each will have polar extremes as far as E and T results. A good (level) and evenly plated (distributed) PTH will have more consistent results and can easily then have variable copper plated thru hole thickness' tested to find what thickness will produce none of what you mentioned. You can pre-bake parts to remove and potential moisture that could increase your "Z" expansion prior to thermal activity. Some tests have indicated that a PTH >1.5 mils reduces PTH anomalies but at >2.0 mils they come back. Other old timers swear that a panel pattern copper plate combo will help with this kind of problem. (??????I dunno...never tried it!) Another important thing that requires attention is to preheat parts prior to extreme thermal activity. (e.g., IR preheat prior to fuse also slow cool ramp as to not thermally shock parts) Good luck. DHH (Groovy) ______________________________ Reply Separator _________________________________ Subject: High Z Axis Expansion Board Materials Author: [log in to unmask] at SMTPLINK-HADCO Date: 12/2/95 5:27 PM We receive questions about plating high Z axis expansion board materials. When the expansion from assembly soldering is too great, surface pads around the holes lift, or the plated barrel cracks. Does anyone have a standard practice to prevent these phenomena when using laminate with great amounts of Z axis expansion (we think more than 6%)? Thicker plating in the hole? Alternate metals plated? Dennis Fritz MacDermid, Inc. 245 Freight Street Waterbury CT 06702 Phone 203-575-5740