SUN’s "Dynamic Retention" printed circuit backplane systems are designed specifically to meet the requirements of MIL-C-28859 and utilizes tuning fork contacts in this compliant press-fit design; which completely eliminates the need for contact-to-panel soldering.  Interconnection configurations of up to 400 contacts and more are made possible by the low insertion force performance of the contact.  Special ultra low-force tuning fork contacts may be specified that yield insertion forces of 2.25 oz. maximum (1.8 oz is typical) per contact.  The modular construction of the two-row and three-row 0.100" x 0.100" grid insulators facilitates the design of high-density row arrays that are compatible with LSI circuitry.  Sophisticated printed circuit process technology is used to produce a wide range of panel designs, from two-sided to complex multilayer; with heavy copper inner layers for applications which require high current carrying capability.

OVERVIEW

The most critical element in the printed circuit backplane is the contact/plated-through hole interface which is designed to provide unsurpassed reliability and performance.  The intregral spring member design of this contact:

- Insures a high-reliability gas-tight connection.

- Results in optimum contact retention within the panel.

- Minimizes panel stress and growth, and distortion of the plated-though hole.

- Enables contacts to be easily replaced with no loss of reliability.

DYNAMIC RETENTION DESIGN

The compliant interface section of the Dynamic Retention contact consists of two bow-shaped springs, which have a geometry determined in conjunction with the stress characteristics of the beryllium copper contact material.  Upon insertion of the contact into the plated-through hole in the glass-epoxy panel, these springs interface with the sides of the hole and resiliently flex forward.  This resillience creates and inverse vector force which acts on the contact to maintain it in intimate association with four vertical sections of the hole.  The flexibility of the spring members also enables the contact to be used effectively in holes with a plated-through tolerance of up to +/- 0.003" insuring optimum performance over a "real-world" range of hole sizes.  The simplicity of the basic design permits each contact to be fabricated as a virtually exact reproduction of every other contact, further insuring consistent and optimum press-fit performance.

PANEL STRESS

In press-fit systems which do not have the resiliency of the Dynamic Retention contact, the printed circuit panel must absorb all of the stress generated by the interference between the contacts and the plated-through holes.  The accumulation of the individual stress results in a total stress which manifests itself in a warped or bowed panel.  The panel also exhibits a tendency to grow excessively and unpredictabiity during contact insertion often resulting in contact misalignment of more than 0.20 T.P. at the board surface.  Because of normal variations in laminate thickness and compositionm and plated-through  hole tolerances, it is extremely difficult to predict the magnitude and direction of  the panel growth.  The resiliency of the Dynamic Retention contact enables it to share interface stress with the panel, thus greatly reducing stress-related effects, and producing a consistently reliable, high quality, and dimensionally accurate backplane.

STRESS PATTERN ANALYSIS

Variation in panel dimensional accuracy is directly related to variation in contact to panel interface stress.  Because of its balanced four-point interaction with the plated-through hole, the Dynamic Retention contact produces a predictable stress pattern that is minimally affected by variations in hole size and other process variables.  A polarized light-stress pattern analysis illustrates the consistency of the Dynamic Retention contact relative to other press-fit contacts.