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What does 7628 prepreg specify?

7628 identifies a woven glass reinforcement style. It does not, by itself, specify a resin system, finished dielectric thickness, dielectric constant or PCB performance class. A usable purchasing description combines the glass style with the manufacturer's material grade, resin content, construction and controlled processing information. The designer then specifies the finished board requirements against which that construction will be reviewed.

This distinction matters when a stackup note says only 鈥�7628, 0.2 mm.鈥� The fabricator still needs to know whether that dimension describes one pressed ply, the complete bondline or an uncured sheet measurement. Two sheets carrying the same fabric designation can contain different resin quantities and produce different dimensional results. Ask for the approved construction table before converting a drawing note into a purchase order.

For the relationship between uncured bonding material and cured core, start with the PCB prepreg guide. This page focuses on selecting and accounting for a 7628 construction. It does not replace the board-level stackup review or prescribe a lamination cycle.

Read the entire construction row

The lists 7628 examples at 45% resin / 0.198 mm and 50% / 0.223 mm. These product-specific values are not universal defaults or stock confirmation.

Keep the supplier's original units alongside the converted value. One mil is 0.0254 mm. A rounded catalogue value should not become a tighter manufacturing tolerance after conversion. If a table lists 7.8 mil and 0.198 mm, the small rounding difference is not evidence of two different products. Use the agreed controlling unit on the drawing.

Where 7628 fits in a multilayer stack

A stackup is a dimensional and electrical model of a finished board, not simply a list of incoming sheets. A 7628 construction can be considered where the proposed bondline and material system suit the board requirements. A relatively large spacing may be useful for a thickness target but may also force wider impedance-controlled traces. Whether the resulting routing geometry is acceptable depends on the actual layer assignment, reference planes and fabrication limits.

Work from the electrical and mechanical requirements toward available constructions. Define the finished board thickness, permitted tolerance, reference layers and any controlled dielectric distances. Ask the fabricator which qualified combinations can meet those requirements. Only then commit the detailed material schedule. This sequence makes alternatives easier to evaluate because the intended result remains visible when a material proposal changes.

Symmetry is a useful review topic, but mirrored layer names do not prove mechanical balance. Copper distribution, material properties, local cutouts and the process history also matter. If the upper and lower bondlines use the same 7628 arrangement, record that fact explicitly. If they differ, explain the reason and obtain a board-level review rather than forcing an asymmetric construction into a symmetric calculator.

Account for a symmetric four-layer construction

Enter supplier-approved pressed contributions and a core dimension that excludes its copper cladding. The worksheet adds one core dielectric, two equal outer bondlines and four equal copper layers. It is intentionally narrower than a general multilayer stackup generator: if your board has unequal copper, mixed plies or more layers, use the released stackup calculation instead.

Worked example: where the 1.600 mm comes from

Consider an illustrative four-layer proposal with a 1.064 mm core dielectric, one 0.198 mm pressed contribution on each side and four 35 碌m copper layers. The accounted total is 1.064 + 2 脳 0.198 + 4 脳 0.035 = 1.600 mm before solder mask and final finish. This example demonstrates dimensional bookkeeping; it is not a recommended universal 7628 stackup or a quotation-ready construction.

Now replace both 0.198 mm contributions with 0.223 mm while holding everything else constant. The sum becomes 1.650 mm. A drawing that still says 1.600 mm therefore needs a deliberate revision to another input, a revised tolerance agreement or a different proposal. Quietly substituting the resin-content row would conceal the change from the designer.

If the total worst-case allowance entered into the tool is 卤0.100 mm, the original model spans 1.500鈥�1.700 mm. That allowance is supplied by the user; the tool does not derive it from a resin specification. Do not obtain a tighter interval by adding unrelated typical values or assuming that all variations cancel. Explain whether a tolerance is a guaranteed bound, a process estimate or a measured sample result.

Resin filling is a separate question

A thickness sum cannot decide whether the resin will fill the copper pattern adequately. A large copper plane and a sparse signal layer present different surface topographies. Within one layer, a dense connector region may sit beside a large cleared area. An average copper percentage is therefore useful context but does not fully describe the local bonding demand.

For a productive review, send the adjacent layer artwork, copper thickness and significant clearance regions. Identify unusual copper islands, heavy features or copper removed around high-voltage areas. The fabricator can examine those details against the proposed resin system and qualified press process. A statement such as 鈥渉igh resin 7628鈥� still needs a numerical construction record and a supplier definition of the term.

The 2116 copper-coverage worksheet illustrates why changed artwork changes recess volume without pretending to calculate resin flow. For a full process explanation, follow the PCB lamination guide. Keep that process discussion separate from the dimensional approval on the released drawing.

Do not use the weave number as design Dk

Electrical behavior depends on the finished composite and the structure carrying the signal. A material data table may describe a particular construction and test method, whereas the circuit model may need a design value characterized for another geometry or frequency. Record the source of the value used by the field solver and keep it with the stackup revision.

For a controlled-impedance route, provide the target impedance, reference layers, copper assumptions, trace geometry and the intended test approach. If the fabricator proposes a different bondline thickness, the trace width or spacing may need revision. The PCB impedance design page owns that calculation task; a 7628 selection alone cannot establish a 50 惟 or 100 惟 result.

An engineering review should also distinguish nominal design from acceptance evidence. A modeled impedance target is not the same as a measured coupon result, and a coupon must represent the agreed construction. Capture any compensation or changed geometry in a revision-controlled record so the next build does not recreate an obsolete assumption.

Compare a defined material allowance

The commercial question is not simply whether 7628 is cheaper than a finer style. Available sheet sizes, ply count, minimum purchasing quantities, panel utilization, processing and verification can outweigh a price-per-area difference. A proposed saving is only useful if both offers cover the same finished board requirements and comparable purchasing scope.

The following worksheet uses your entered prepreg rate and panel assumptions. It separately shows purchased prepreg area, processing allowance and setup. It does not substitute an FR-4 market rate or invent a 7628 price. Core, foil, drilling, finish and tests remain outside the subtotal unless your documented processing allowance expressly includes them.

For example, 100 ordered boards, ten usable positions per panel, 0.25 m虏 of purchased sheet area per ply and two plies across the complete stack require ten panels and 5 m虏 of prepreg in this simplified purchasing model. At an illustrative 20 currency units per m虏, the prepreg allowance is 100 units. This is a scoped material calculation, not the price of 100 completed boards. Pack sizes and minimum orders need a separate supplier check.

Prepare the RFQ and acceptance record

Send one consistent file set with the board identifier, revision, quantity, dimensions and intended stackup. Identify which dimensions are mandatory and which are open to an equivalent proposal. Name the material system when it is contractually required; if alternatives are permitted, state which electrical, thermal, mechanical and compliance requirements must remain satisfied.

Ask for a response that identifies the proposed construction, relevant tolerances, open engineering questions and any departure from the drawing. For a repeat order, confirm that a substitution has not changed the resin system or glass arrangement. The PCB manufacturing service is the commercial route for the completed board; this material page supplies a focused input to that review.

During receiving inspection, match the board revision and agreed records rather than attempting to identify prepreg through solder-mask color. Cross-sections, dimensional results and material traceability answer different questions. The required evidence and sampling belong in the purchase and quality agreement. A photograph can illustrate the board but cannot certify the internal bonding construction.

Practical questions about 7628 prepreg