| Anyone who needs to order Printed Circuit Boards will find this document invaluable. An amateur or start-up company using this will be seen as "professional" by the PCB manufacturer. Even some time-served professionals fail to use documents such as this but really ought to. It is your protection against misunderstandings and incorrect specifications. Use the document and alter it to suit your particular requirements.
BLOGRIGGS LTD. PROCUREMENT SPECIFICATION FOR PRINTED WIRING BOARDS
1.
Scope
This specification details the acceptance standards for rigid, single- and double-sided PWBs with plain holes and forms part of the purchase order. The requirements of this Specification may, however, be overruled by the CDS or by the Drawing Package or by a Written Concession.
2.
Standards - One of the following standards will apply:
2.1 BS6221:1982 - For "Commercial Quality" boards not intended to be used for Surface Mount applications.
2.2 BS9763:1977 - For "High Reliability" applications, including Surface Mount.
2.3 DEF STAN 59-48 for defence contracts.
3. Related Documents
3.1 BS4584:1972 Part 1. Metal Clad Base Material. Methods of Test.
3.2 BS4584:1972 Parts 2 and 3. Metal Clad Base Material. Specs.
3.3 NEMA L1-1-1965 Part 10. Copper Clad Laminates.
3.4 BS219 Tin-Lead Plating.
3.5 BS4292 Gold Plating.
3.6 BS6096 Ink.
3.7 BLOGRIGGS Ltd. Purchase Order.
3.8 BLOGRIGGS Ltd. Customer Detail Specification.
3.9 Photographic artwork.
3.10 D & D Code of Practice part SLCS section 10.
4.
Definitions
4.1 "The Company" refers to BLOGRIGGS Ltd.
4.2 "PWB" is an abbreviation of Printed Wiring Board.
4.3 "CDS" is an abbreviation of "Customer Detail Specification".
4.4 "SMD" is an abbreviation for "Surface Mounting Device".
4.5 Side 1 refers to that side of the board which contains component identification. Side 2 is the opposite side which will be soldered.
4.7
Purchase Order
The printed wiring boards shall be manufactured in accordance with the CDS, artworks and drawings which accompany the Purchase Order. If any necessary detail should be omitted from the Purchase Order, however, the PWB manufacturer shall obtain in writing from The Company such information as is needed to complete the order.
4.8
Customer Detail Specification
The CDS lists the relevant artworks and drawings and describes any special requirements which conflict with - or are not included in - the drawings. In the case of conflict the CDS shall take precedence over drawings and specification.
5.
Photographic artwork
5.1 Photographs will be supplied on high stability 0.18mm (0.007") polyester film; the positive is correct when read with emulsion uppermost and the negative is correct when read with the emulsion beneath. Copies of the negatives will be used by The Company for its Goods Receiving Inspection.
5.2 It is the responsibility of the PWB manufacturer to ensure that the photography is of an acceptable quality with regard to definition and registration accuracy.
5.3 The photography supplied is the property of The Company. It must be retained in a controlled library and updated or returned to The Company when required.
6.
Packing
The PWBs shall be supplied in a clean, dry condition in sulphur-free protective wrappings. Dust shall be minimal and there shall be no sign of damage. A Certificate of Conformity shall be supplied with every delivery.
7.
Base Laminate
7.1 The board material shall be epoxide resin bonded, woven glass fabric; flame retardant grade, translucent type, nominal thickness 1.6mm (0.062"), clad with 305g/sq.m (1 oz) copper, nominal thickness 35um (0.0014").
7.2 The material must conform to:
BS4584:1972 part 3, type EP-GC-CU-3, close tolerance thickness, or
NEMA-L1-1-1965 Grade FR4 General purpose flame resistant material; Class 2 thickness tolerance,
or
NEMA-L1-1-1965 Grade FR5 General purpose temperature and flame resistant material; Class 2 thickness tolerance.
8.
Holes
8.1 Holes shall be drilled and free from burrs, epoxy smearing, protruding fibres and delamination.
8.2 The final hole size shall be in accordance with the drawings.
8.3 The tolerance on hole diameter will be as follows:
up to 1.0mm (0.039") = +/- 0.05mm (0.002").
- 0mm to 2.4mm (0.094") = +/- 0.10mm (0.004").
- 5mm (0.098") or greater = +/- 0.15mm (0.006").
8.4 The hole shall be within the area defined by the land and, where the hole is offset towards an adjoining conductor, the radial distance between the hole and the edge of the land shall not be less than 0,1mm
9. Conductors
9.1 The final plated conductor width shall be the design width, as measured on the production film, within the following limits:
Conductors from 0.25mm to 0.5mm = +/- 0.05mm.
Conductors from 0.5mm to 1.2mm = +/- 0.10mm.
Conductors from 1.2mm upwards = +/- 0.15mm.
9.2 The gap between plated conductors (and pads) shall not be reduced by more than an average 0,2mm of its design width or locally by more than 0,25mm at any point.
9.3 Average copper track thickness shall be at least 25um and not less than 20um locally at any point.
9.4 There shall be no evidence of lifting of conductors from the base material.
9.5 There shall be no fine line cracks or breaks in conductors or short circuits between them.
9.6 Isolated defects in conductors 0.5mm wide and greater are permitted if they do not reduce conductor width by more than 25% and are not longer than the conductor design width and not closer than 12mm to any other similar defect on the same conductor. Defects are not acceptable where a conductor joins a solder pad.
9.6 The minimum peel strength on test pattern width measured in accordance with BS9760 para 1.2.5.2.1 shall be 1.4 kN/m in the case of glass epoxide laminate.
9.7 When tested by the method stated in BS9760 para 1.2.5.1.1 the minimum pull-off strength on test pattern width must not be less than 60N in the case of glass epoxide laminate.
10.
Tin-Lead Plating
10.1 For boards intended for use with SMDs a coating of tin-lead to BS219 Grade A or Grade K shall be applied to a thickness of 10um +5um /- 2um measured after all processing. There shall be no localised unsymmetrical build up of solder on pads intended for SMDs. For boards NOT intended for SMDs the final solder thickness on pads is less critical. Consequently, it may be 8um to 40um and need not be even.
10.2 The tinning shall exhibit a bright, clean surface free from "icicles" or dewetting and must not obstruct holes. There shall be no unprotected copper surface exposed on any part of a board. The thickness of tin-lead beneath the solder resist coating should be minimized and must not exceed 12um.
10.3
Explanatory notes: the tin-lead coating facilitates soldering after storage and protects the copper conductor pattern against tarnishing and corrosion. Pure tin is prone to "whiskering" which causes short-circuits, consequently pure tin should not be used. Excessive tin-lead beneath the solder resist coating can cause wrinkling or cracking of the coating. Uneven tin-lead thickness or build up on pads intended for SMDs can result in bad soldered joints or even component damage as the automatic placement equipment tries to position a component squarely.
11. Gold Plating
11.1 Areas required to be gold plated shall be electro-plated with a minimum thickness of 5um low stress Nickel to DTD919B followed by hard gold to DTD938 of minimum 99% purity and minimum thickness 1um in accordance with BS4292. The hardness of the gold shall be within the range 100 - 140 V.P.N.
11.2 The plating shall meet the requirements of BS6221 for adhesion, porosity and peel strength. Stress lines and cracks are NOT acceptable.
11.3 The edge of a board with gold plated edge connectors shall be finished for its entire length with a 0.4mm to 0.8mm 45' chamfer.
11.4
Explanatory note: It should be recognised that the porosity requirement may not be met by a gold plating whose average thickness is less than 2.5 microns. It is accepted, however, that a cut and chamfered board edge will unavoidably expose the bare copper of the edge connectors.
12. Solder Resist
12.1 Solder resist shall comply with BS6096, shall be continuous and shall not encroach on solder pads or test pads (but see note). Encroachment in to holes is not permitted.
12.2
Explanatory Note: Around the perimeter of each pad a minimum clearance of 0.25mm is required for non-photo-definable resist or 0.10mm for photo-definable resist or 0.5mm for peelable resist. This tolerance must be included in the artwork design if encroachment is to be avoided.
12.3 Sample boards or parts thereof shall not exhibit any blistering or visible deterioration of the resist when placed for 30 minutes in an oven whose air temperature is 120'C followed immediately by immersion in a bath of tin-lead solder for a maximum of 5 seconds at 260'C. In addition, if the resist is a peelable type, it shall remain so after the conditioning specified above.
12. No bare copper shall be visible (exception: see #11.3). However it is recognised that, on edges and sharp corners, the resist resin may be present whilst the pigment is not visible. In case of doubt a suitable chemical staining agent will be used to test the apparently exposed copper.
13. Marking
13.1 The component designation overlay shall be printed in yellow on side 1 of the board.
13.2 Any misregistration of the marking shall be minimised to avoid error in assembly or rework. The marking shall be clear and legible. The marking shall not enter any hole (but see note).
13.3 After the conditioning specified in #12.3 there shall be no visible deterioration of the marking. Nor should the marking fade or lift when rubbed lightly with a cotton cloth soaked in water.
13.4 The marking ink shall comply with BS6096
13.5
Explanatory Note: The design should allow for a mis-registration of up to 0,5mm to avoid encroachment of the marking ink into any hole.
14. Identification
14.1 The PWB manufacturer's three-letter code and either his batch code, or the year and week of manufacture, shall be marked indelibly in copper or ink on a clear area of side 2 of the PWB. The code shall be in a position which is legible after assembly of components and may, in the case of a PWB intended for SMDs, be on side 1 of the PWB. The position and method of marking must, however, be agreed by The Company in writing before delivery.
14.2
Explanation: the marking allows immediate identification if the need arises to segregate a batch of PWBs for investigation.
15. Carbon Ink
15.1 The term "Carbon Ink" is used to describe a suspension of conductive particles in a resin base. Carbon Ink may be applied to a PWB by a silk-screen process to produce conductors of a specific resistance or contacts for use with a conductive elastomer.
15.2 The Carbon Ink shall be applied directly on bare copper and not tinned copper. No bare copper shall be left exposed on the final PWB.
15.3 The curing of the carbon Ink shall not cause warping of the PWB but shall be adequate to ensure good adhesion and long-term stability of the resistance value. The Adhesion and stability of the Carbon Ink shall not be affected by any solvents commonly used in the soldering process.
15.4 The Carbon Ink shall be unaffected by the conditioning described in #12.3.
15.5 PWBs using Carbon Ink shall be subject to Type Approval by The Company and first-off samples should be supplied for the purpose, together with details of the type of Carbon Ink, the application process and curing process. Should any of these parameters subsequently be altered, The Company shall be informed at the earliest possible date and further samples supplied for verification.
16.
Bow
When the PWB is placed on a flat plate such that all four corners rest on the plate, the maximum vertical distance between the plate and the underside of the PWB shall not exceed .75mm for every 100mm length of board. For additional fractions of 100mm the maximum permitted bow shall be calculated pro-rata.
17.
Twist
When the PWB is placed on a flat plate such that three corners rest on the plate, the maximum vertical distance between the plate and the corner which is not in contact shall not exceed .75mm for every 100mm diagonal length of PWB. For additional fractions of 100mm the maximum permitted twist shall be calculated pro-rata.
18.
Multiple Boards
Where the size of PWBs permits, it may be preferable for the manufacturer to supply a "mother board" containing a number of identical PWBs, each with a semi-sheared or a routed outline. Such an arrangement will be by prior agreement with The Company and the provisions of #16 and #17, above, shall refer to the individual PWBs and not to the mother board, except that in the case of severe bow or twist which prevents satisfactory component placement or flow-soldering, The Company shall have the right to reject the materiel or to claim such compensation from the supplier as would cover the additional cost of handling the PWBs individually.
19.
Concessions
In the event that the manufactured PWB fails to meet the specification, the manufacturer may submit representative worst-case samples for inspection. On receipt of a Concession, signed by representatives of all departments concerned, the manufacturer may, according to the timescales of contract, supply the conceded quantity of PWBs, subject to the requirements of the concession, if any.
20.
Specification
In the event that the PWB manufacturer feels that he is incapable of meeting the requirements of the specification he may apply to The Company for a relaxation of the specification which, if granted, might result in a permanent amendment to the procurement specification or a Written Concession relating to a limited quantity.
21.
Assessment
The PWB manufacturer shall provide every reasonable facility and assistance to The Company's Representative, should the need for Vendor Assessment arise.
22.
Inspection
The PWB manufacturer shall, on request, provide copies of sample measurements taken before delivery to prove that the delivered materiel met the specification.
23.
Approval
The Supplier shall have full approval for the category of board to which the Purchase Order applies.
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