SE462944B

SE462944B - Electrical screening device for a printed circuit board and method for manufacturing the device

Info

Publication number: SE462944B
Application number: SE8900335A
Authority: SE
Inventors: W A P Dick
Original assignee: Ericsson Telefon Ab L M
Priority date: 1989-01-31
Filing date: 1989-01-31
Publication date: 1990-09-17
Also published as: SE8900335L; SE8900335D0

Abstract

A screening device for a circuit board containing components 1,1a-1c which screens the circuit board 1 and its components 1a-1c from external interference fields and at the same time screens high-frequency radiation from the board's circuits. The device consists of an insulating layer which is in close contact with the board and its components. Over this layer there is an adhesive, electrically conductive layer 4. The invention also concerns a method for manufacturing the screened device. <IMAGE>

Description

10 15 20 25 462 944 2 ponentbestyckat kretskort.Anordningen jämte förfarandet för dess tillverkning är därvid kännetecknade sa som framgår av patentkrav 1 respektive 2. 10 15 20 25 462 944 2 component-equipped circuit board.The device and the procedure for its manufacture are thereby characterized as claimed in claims 1 and 2, respectively.

FIGURBESKRIVNING Uppfinningen skall närmare beskrivas med hänvisning till bifogad ritning där figur 1-4 visar de olika stegen att tillverka skärmningsanordningen enligt uppfinningen medelst det föreslagna förfarandet.DESCRIPTION OF FIGURES The invention will be described in more detail with reference to the accompanying drawing therein Figures 1-4 show the different steps to manufacture the shielding device according to the invention by means of the proposed method.

Figur 5 visar skärmningsanordningen enligt uppfinningen i ett tvärsnitt pa ett kretskort.Figure 5 shows the shielding device according to the invention in a cross section of one circuit boards.

UTFÖRINGSFORMER I figur l visas ett kretskort l sett fran dess ena smalare sida. Kortet l är färdigbestyckat med eletroniska komponenter, av vilka komponenterna la-lc är synliga i figuren. Dessa komponenter kan utgöras av exempelvis mikrokretsar i form av DlP-kapslam Kretskortets 1 kontaktstift bildar en kontaktlist 2, som skall göra kontakt med kortjacket hos ett stativ (ej visat). Kretskortet 1 antas ha rektangulär form och dess kontaktstift 2 är anordnade utmed ena längs- gaende sidan. I det första förfaringssteget enligt figur l paläggs en dubbel- häftande tejp 5 utmed kretskortets längd och i närheten av dess kontaktorgan 2.EMBODIMENTS Figure 1 shows a circuit board 1 seen from one of its narrower side. The card l is pre-equipped with electronic components, of which components la-lc are visible in the figure. These components can consist of, for example, microcircuits in form of DlP capsule sludge The circuit board's 1 contact pin forms a contact strip 2, which must make contact with the card jack of a tripod (not shown). Circuit board 1 is assumed have a rectangular shape and its contact pins 2 are arranged along one longitudinal going side. In the first process step according to Figure 1, a double adhesive tape 5 along the length of the circuit board and in the vicinity of its contact means 2.

Det är även möjligt att stryka pa ett smältlim, dvs ett lim som efter strykningen utmed kortet stelnar men som smälter och blir häftande vid uppvärmning.It is also possible to apply a hot melt adhesive, ie an adhesive as after the ironing along the card solidifies but melts and becomes sticky heating.

Figur 2 visar det andra steget i förfarandet. En termoplastpase 3 har trätts över hela kretskortet l och pasens 3 öppning befinner sig utmed kretskortets kontaktlist 2. Det är givetvis möjligt att trä påsen 3 över kretskortet 1 så att pasens öppning befinner sig utmed en annan kantyta hos kortet l. Det är emellertid fördelaktigt att ha pasens öppning sammanfallande med kontakt- listen 2, eftersom påsen (i ett senare steg) skall skäras upp sa att kontaktlisten friläggs, se nedan.Figure 2 shows the second step in the process. A thermoplastic phase 3 has been crossed the entire circuit board 1 and the opening of the pass 3 are located along the circuit board contact strip 2. It is of course possible to thread the bag 3 over the circuit board 1 so that the opening of the pass is located along another edge surface of the card l however, it is advantageous to have the opening of the pass coincide with the contact strip 2, since the bag (at a later stage) is to be cut open so that the contact strip exposed, see below.

I tredje steget evakueras påsen 3 enligt pil A, figur 2 så att denna trycks ihop Ü-w 10 15 20 25 330 'I 46 944 3 och sa att dess innerytor tätt anligger mot kortet l och dess komponenter la-lc under det yttre trycket. Smältlimmet eller tejpen 5 är fastsatt utmed kontakt listen 2 och vid evakuering av pasen 3 kommer dess inneryta vid kontaktlisten 2 att häfta fast mot kretskortet l medelst limmet (tejpen). Härigenom har kretskortet 1 och dess komponenta la-lc försetts med ett helt isolerande skikt 3.In the third step, the bag 3 is evacuated according to arrow A, figure 2 so that it is compressed Ü-w 10 15 20 25 330 'IN 46 944 3 and said that its inner surfaces abut closely against the card 1 and its components 1a-1c under the external pressure. The hot melt adhesive or tape 5 is attached along the contact the strip 2 and when evacuating the pass 3 its inner surface comes at the contact strip 2 to adhere to the circuit board l by means of the glue (tape). Hereby has the circuit board 1 and its components 1a-1c are provided with a completely insulating layer 3.

I det fjärde steget enligt figur 4 doppas kretskortet med det isolerande skiktet 3 i en elektriskt ledande lack sa att denna bildar ett elektriskt ledande skikt 4 som helt täcker det isolerande skiktet. Även kontaktlisten 2 är nu åtminstone delvis täckt av bade det isolerade skiktet 3 och det elektriskt ledande siktet 4. I sista steget skärs därför det ledande och isolerande skiktet 3 resp 4 utmed den kant som befinner sig i närheten av kontaktlisten 2 för att frilägga denna.In the fourth step according to Figure 4, the circuit board is dipped with the insulating layer 3 in an electrically conductive varnish said that it forms an electrically conductive layer 4 which completely covers the insulating layer. Also the contact strip 2 is now at least partially covered by both the insulated layer 3 and the electrically conductive screen 4. I the last step, therefore, the conductive and insulating layer 3 and 4, respectively, are cut along it edge located near the contact strip 2 to expose it.

Skärningen utförs exempelvis medelst en kniv 6 och sa nära som möjligt det limmade eller tejpde skiktet 5. Figur 5 visar den slutgiltiga utformningen av skärmninganordningen enligt uppfinningen. Den omsluter saledes hela kretskor- tet l och dess komponenter la-lc utom kontaktlisten 2.The cutting is performed, for example, by means of a knife 6 and as close as possible to it glued or taped layer 5. Figure 5 shows the final design of the shielding device according to the invention. It thus encloses the entire circuit tet 1 and its components la-lc except the contact strip 2.

Pasen 3 kan som ovan nämnts bestå av en termoplastisk folie tillverkad av polykarbonat (exempelvis "Makrolon" (Bayeﬂ). Den elektriskt ledande lacken kan besta av kommersiellt tillgänglig Ni-lack, exempelvis "Electrodag" 440-AS (Acheson).Step 3 can, as mentioned above, consist of a thermoplastic foil made of polycarbonate (for example "Macrolon" (Baye ﬂ). The electrically conductive varnish may consist of commercially available Ni-lacquer, for example "Electrodag" 440-AS (Acheson).

Som alternativ till att evakuera påsen 3 för att fa denna att tätt smita at kring kortet 1 och dess komponenter la-lc, kan man använda en pase av sadant termoplastiskt material att denna krymper vid uppvärmningen av smältlimmet.As an alternative to evacuating the bag 3 to make it sneak around card 1 and its components la-lc, one can use a phase of such thermoplastic material that it shrinks when the hot melt is heated.

Denna uppvärmning används således även för att krympa pasen 3.This heating is thus also used to shrink the pass 3.

Om mekanisk förstärkning av den ledande lacken visar sig vara önskvärd, sa kan det ledande skiktet 4 förstärkas genom kemisk beläggning med koppar eller nickel, eventuellt med bada dessa metaller. Beläggningen blir da även diffu- sionstät.If mechanical reinforcement of the conductive varnish proves to be desirable, then can the conductive layer 4 is reinforced by chemical coating with copper or nickel, possibly by bathing these metals. The coating will then also be diffused. sionstät.

För att undvika den kapacitiva kopplingen till jord och fa en bättre avledning av det störande fältet kan man ansluta det ledande skiktet 4 till stativet. Detta kan enkelt utföras genom att klämma fast eller löda byglingar fran skiktet 4 till nagon av stativets jordförbindelser.To avoid the capacitive connection to earth and get a better diversion of the interfering field, the conductive layer 4 can be connected to the stand. This can be easily performed by clamping or soldering stirrups from layer 4 to any of the stand's ground connections.

Claims

4 4 6 2 9 4 4 IN PATENT REQUIREMENTS

An electrically shielding device for a circuit board (1), which is equipped with electrical / electronic components (1a-1c) and provided with connectors (2) along at least one side for connecting the circuit pattern of the circuit board to external connections of a stand or the like, characterized by an insulating layer (3) which completely encloses the circuit board (1) and its components (1a-1c) with the exception of said connectors (2) and an electrically conductive layer (4) on this layer which adheres to the insulating member. layer (3).

Method for manufacturing an electrically shielding device for a circuit board provided with a contact strip (2) according to claim 1, characterized in that the circuit board (1) and its components (1a-lo) are packaged in a bag (3) of insulating material so that the bag (3) completely encloses the circuit board and its components, that the bag (3) is treated in such a way that it abuts against the circuit board and its components, whereby an insulating layer is formed, that the circuit board together with the insulating layer (3) dipped in an electrically conductive varnish so that an electrically conductive layer (ä) is formed over the insulating layer (3), and that the electrically conductive and the insulating layer (4 and 3, respectively) are cut along and in the vicinity of the contact strip (2) of the circuit board.

3. A method according to claim 2, characterized in that said treatment of the bag (3) comprises evacuation so that it, under the influence of the external pressure, closely abuts against the circuit board and its components.

A method according to claim 2, characterized in that said treatment of the bag (3) involves heating the same so that it shrinks to a close abutment against the circuit board and its components.